New Refractive 

Surgery Procedures 

and Their Implications 

for Aviation Safety

Van B. Nakagawara

Kathryn J. Wood

Ron W. Montgomery

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

April 2006

Final Report

DOT/FAA/AM-06/9

Office of Aerospace Medicine

Washington, DC 20591
2

NOTICE

This document is disseminated under the sponsorship 

of the U.S. Department of Transportation in the interest 

of information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine 

technical reports are available in full-text from the Civil 

Aerospace Medical Institute’s publications Web site: 

www.faa.gov/library/reports/medical/oamtechreports/index.cfm
i

Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-06/9 

4. Title and Subtitle 5. Report Date 

New Refractive Surgery Procedures and Their Implications April 2006 

for Aviation Safety 6. Performing Organization Code 

 

7. Author(s) 8. Performing Organization Report No. 

Nakagawa VB, Wood KJ, Montgomery RW 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

FAA Civil Aerospace Medical Institute 

P.O. Box 25082 11. Contract or Grant No. 

Oklahoma City, OK 73125 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, DC 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

 

16. Abstract 

Since the early 1980s, civil airmen have been allowed to correct refractive error (i.e., myopia, hyperopia, 

astigmatism) with corrective surgery. Prior Federal Aviation Administration research studies have shown that the 

number of civil airmen with refractive surgery continues to increase. A study that reviewed refractive surgery use 

in civil airmen for the years 1994-96, reported that the largest percentage had radial keratotomy (RK). A similar 

study that reported on the years 1996-2001, however, showed that there had been a substantial increase in the 

percentage of airmen with laser refractive surgery, i.e., photorefractive keratectomy (PRK) and laser in situ 

keratomileusis (LASIK). A reference guide on refractive surgery was published in September of 1998 

(DOT/FAA/AM-98/25); however, at that time long-term clinical data on PRK and LASIK were not available. 

The introduction of new refractive surgical techniques (e.g., laser epithelial keratomileusis [LASEK], laser 

thermal keratoplasty [LTK], conductive keratoplasty [CK], IntacsTM, phakic IOLs, and presbyopia surgeries) and 

technology (e.g., wavefront-guided systems, Femtosecond Lasers, inlays, and onlays) has further added to 

concerns regarding the use of refractive surgical procedures by aviators. In order to provide the aviation 

community with information to formulate administrative decisions and policies associated with existing and 

emerging refractive surgical procedures, this paper reviews current procedures and discusses their applicability in 

the civil aviation environment. 

 

17. Key Words 18. Distribution Statement 

 

 

Aviation Vision, Aeromedical Certification,

Refractive Surgery 

Document is available to the public through the 

Defense Technical Information Center, Ft. Belvior, VA 

22060; and the National Technical Information 

Service, Springfield, VA 22161 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 45 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

iii

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

REFRACTIVE CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Myopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Hyperopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Astigmatism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Presbyopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

REFRACTIVE ERROR MODIFICATION TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Radial Keratotomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Photorefractive Keratectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Laser in situ Keratomileusis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Laser Epithelial Keratomileusis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Thermokeratoplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Conductive Keratoplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

IntacsTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Clear Lens Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

NEW TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Phakic Intraocular Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

PRESBYOPIA SURGERY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Anterior Ciliary Sclerotomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Laser Presbyopia Reversal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Surgical Reverse Presbyopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

WAVEFRONT TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

FEMTOSECOND LASER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Inlays And Onlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

AEROMEDICAL ISSUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

SUMMARY AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
iv

FIGURES AND TABLES

Figure 1. Myopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Hyperopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 3. Astigmatism.............................................................. 2

Figure 4. Accommodation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 5. Radial Keratotomy (RK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 6. Photorefractive Keratectomy (PRK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 7. Microkeratome cutting a corneal flap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 8. Excimer laser ablating tissue from corneal stroma during LASIK . . . . . . . . . . . . . . . . . . . . . . 7

Figure 9. Creation of the LASIK flap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 10. Laser epithelial keratomileusis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 11. Laser Thermal Keratoplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 12. Conductive Keratoplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 13. Steepening of the cornea to correct for hyperopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 14. Intacs semi-circular plastic inserts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 15. Array® Multifocal IOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 16. CrystaLens® Accommodating IOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 17. An anterior chamber phakic IOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 18. Anterior sclerotomy involves making radial incisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 19. SurgiLight IR-3000 infrared laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 20. Surgical reversal of presbyopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 21. Insertion of scleral expansion bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 22. IntraLase FS Laser Keratome procedure........................................ 20

Figure 23. Placement of corneal onlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 24. Inlay procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 25. Refractive surgery, by type, in civil airmen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 26. Refractive surgery, by type, in civil airmen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 1. PRK percentages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Table 2 Patient-reported satisfaction and complications after PRK . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Table 3. Percentages of refractive procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 4. Patient reports of satisfaction and complications after myopic LASIK . . . . . . . . . . . . . . . . . . 9

APPENDIX A. Eye diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1

APPENDIX B. Refractive surgery options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B1
1

New Refractive Surgery Procedures and

Their Implications for Aviation Safety

INTRODUCTION

Refractive error is a defect of the eye that prevents light 

rays from being brought to a single focus on the retina.

To see clearly, refractive errors are normally corrected 

with ophthalmic lenses (e.g., glasses, and contact lenses) 

or refractive surgery. There are three principal types of 

refractive conditions: myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (light rays from a 

single point object are not focused at a single point on the 

retina). Although not a refractive condition, presbyopia (a 

reduction of accommodative ability occurring with age), 

which normally occurs about 40 years of age, results in 

blurred vision at near requiring the use of multifocal or 

reading glasses.

More than 155 million Americans are dependent on 

spectacles or contact lenses to achieve a quality of vision 

satisfactory for their daily needs (1). About 16% of these 

individuals wear contact lenses (2). In the last 25 years, 

there has been increasing marketing and advertising pressure on those with refractive error advocating a lifestyle 

free of glasses or contact lenses. The perception of lifestyle 

improvement is a major factor that influences a patient 

to seek refractive surgery as an alternative method of 

refractive correction.

In September of 1998, the Office of Aviation Medicine 

Report “The Aeromedical Certification of Photorefractive 

Keratectomy in Civil Aviation: A Reference Guide” (3) 

was published to provide information to those responsible 

for making certification decisions regarding two new refractive surgery procedures (Photorefractive Keratectomy 

[PRK], Laser1 in situ Keratomileusis [LASIK]) and to 

assist Aviation Medical Examiners in counseling civil 

airmen who were interested in having refractive surgery.

These procedures have continued to evolve and grow in 

popularity since that time. In addition, there has been an 

influx of new refractive surgery procedures. This document reviews long-term effects and visual performance 

issues of patients with PRK and LASIK that were not 

available when the original reference guide was published 

and discusses the benefits and risks associated with the 

use of new refractive procedures.

REFRACTIVE CONDITIONS

Myopia

A myopic or nearsighted person has difficulty seeing 

distant objects clearly. Myopia is rare at birth, normally 

manifesting after the 4th year of life, with progression 

relatively constant until the time of puberty, when it 

may progress more rapidly. The condition occurs when 

the eyeball grows too long or when the cornea is curved 

too steeply for the overall length of the eye, causing 

the refracted image to be focused in front of the retina 

(Figure 1). Normally, myopia becomes stable at physical 

maturity. Therefore, between the ages of 20 and 40 years, 

correction may remain essentially unchanged (4). Even 

small amounts of myopia result in distant objects being 

considerably blurred. For example, a -1.00 Diopter (D) 

refractive error would result in unaided vision of 20/40 

to 20/60 Snellen acuity. While eyeglasses or contact 

lenses are the primary treatment for myopia, these devices 

can be a hindrance in some occupations or recreational 

activities. Lenses for high myopia have thick edges, and 

the optical image is distorted by minification and optical 

aberrations. The exact cause of myopia remains unknown.

It is believed that heredity and environment play a role 

in myopic development. When both parents are nearsighted, their children have a greater chance of developing 

myopia. Environmental factors, such as reading in dim 

lights or doing excessive amounts of close work, may 

contribute to myopia. About 30% of the population in 

North America is myopic (2).

Figure 1. Myopia

1

Laser will be the term used in this manuscript for LASER 

(Light Amplification by Stimulated Emission of Radiation) 

devices.
2

Hyperopia

Hyperopia, or farsightedness, is a disorder in which 

vision is more blurred at near. This occurs when the eye 

is too short in length or the cornea is too flat, causing 

an image to be focused behind the retina (Figure 2). At 

birth, eyes are normally hyperopic (about +2.00 or +3.00 

D). With aging, the eye normally lengthens. (Note: Each 

millimeter that the eye is too short is equal to 3.00 D 

of hyperopic refractive change [4].) Statistics are vague 

on the prevalence of hyperopia. Some epidemiological 

studies incorrectly incorporate presbyopia, which also 

requires plus power lenses, as part of the total percentage 

of hyperopia in the population. An estimated 40% of 

Americans are hyperopic (1). Many of these hyperopes 

are children who are able to overcome their farsightedness due to their ability to accommodate. It is not until 

most hyperopes are in their late thirties or early forties 

that they experience clinical symptoms with hyperopia 

they have had their entire life.

Astigmatism

Astigmatism causes blurred vision when looking at 

objects both near and distant. The cornea is normally 

smooth and uniformly curved on all sides; however, with 

astigmatism the cornea is irregularly curved (steeper in 

one meridian) (Appendix A). This irregular shape causes 

light to bend, or refract, causing light rays to become focused at multiple points, which results in distorted vision 

at any distance. Astigmatism may occur in addition to 

myopic or hyperopic conditions (Figure 3). At birth, the 

cornea is usually spherical; however, by 4 years of age the 

cornea shape changes. With-the-rule astigmatism occurs 

as the vertical corneal meridian steepens with age, while 

against-the-rule astigmatism occurs as the horizontal 

corneal meridian steepens with age (4). Irregular astigmatism most often occurs if the cornea has been damaged 

by trauma, inflammation, scar tissue, or developmental 

anomalies. This type of astigmatism normally cannot 

be completely corrected by ophthalmic spectacle lenses 

due to the lack of any geometric form from the irregular 

corneal surface.

Presbyopia

Presbyopia (the inability to focus at near) occurs when 

the crystalline lens loses its ability to accommodate or 

change in shape (Figure 4). Before developing presbyopia, the crystalline lens becomes flatter or thinner when 

focusing on objects at distance and becomes rounder 

or thicker when focusing on objects at near. Virtually 

everyone experiences some degree of presbyopia by early 

to mid-forty years of age. The ability to accommodate 

continues to decrease until about 55 years of age. Presbyopia can occur in combination with any other type of 

refractive error and can complicate these visual conditions. For example, mildly farsighted individuals may 

find that they need reading glasses to see at near, while 

nearsighted people may need bifocals so that they can 

see comfortably at all distances.

REFRACTIVE ERROR 

MODIFICATION TECHNIQUES

Eye care physicians have used many different techniques 

in an attempt to alter or reduce refractive error. Due to 

the limited success and complications, refractive surgeons 

no longer use many of these techniques (e.g., cycloplegia, 

clear lens extraction, and scleral reinforcement) (5). Additionally, there were several refractive procedures that 

concentrated on modifying the anterior surface of the 

cornea, which supplies 44 of the 66 D (2/3) of the eye’s 

total refractive power (Appendix A). These refractive 

surgical procedures (e.g., keratomileusis, keratophakia, epikeratophakia, stromal thermokeratoplasty, and 

Figure 2. Hyperopia

Figure 3. Astigmatism

Figure 4. Accommodation
3

intrastromal corneal ring) were more complex and had 

many complications, which led to their being discontinued (5). This paper will review refractive procedures 

that are currently being used by refractive surgeons and 

new procedures that are still in the investigational phase 

or being performed on a limited basis.

Radial Keratotomy

Sato of Japan first used radial keratotomy (RK) on a 

wide scale in 1953. In the early 1970s, Dr. Fyodorov of 

Russia considerably refined this technique. Since the late 

1970s when it was first introduced in the United States, 

RK has been performed on more than a million Americans. The RK procedure involved making radial incisions 

on the peripheral cornea. These incisions weakened the 

cornea and allowed intraocular pressure to push the peripheral cornea out and flatten the apex, which reduces 

myopia (Figure 5). (Note: See Appendix B for surgical 

criteria table.)

In March 1982, a multi-center trial with 10 participating surgeons was designed to determine the outcome of 

a single, standardized technique for myopia (Prospective 

Evaluation of Radial Keratotomy or PERK Study), which 

evaluated 757 eyes with a mandated eight-incision procedure. PERK study data at 5 years reported that two-thirds 

of patients no longer wore any correction, most of the 

other one-third only wore a correction part time, 60% 

were within ± 1.00 D of correction, and 88% had uncorrected visual acuity of 20/40 or better (6). At 5 years, only 

13% of eyes reported progressive hyperopic shift of 1.00 

D or more, but by 10 years, 43% of eyes had changed 

in the hyperopic direction by 1.00 D or more (6-9). Of 

the 374 patients (88%) who returned for the 10-year 

examination, 70% reported not wearing spectacles or 

contact lenses for distance vision, 60% were still within 

± 1.00 D of correction, and 85% had uncorrected visual 

acuity of 20/40 or better (7). In addition, other long-term 

studies reported further complications such as reduced 

corneal strength (10-13), fluctuation of vision (14-19), 

glare (20-23), poor refractive predictability (7,24,25), 

and altitude-induced corneal changes (26-29). With 

the advent of new laser procedures and many reports on 

both short- and long-term complications from RK, this 

procedure is rarely used today.

Photorefractive Keratectomy

The excimer laser has been used in ophthalmic and 

refractive applications since the early 1980s. The laser 

employs a 193 nanometer (nm) ultraviolet-C light, which 

is emitted as an excited dimer of the argon fluoride gas 

mixture. This high-energy laser light causes an almost 

instantaneous vaporization of small amounts of the cornea 

by direct photochemical disruption of molecular bonds, 

with minimal impact on neighboring ocular tissue (30,31).

The excimer laser was initially approved by the Food and 

Drug Administration (FDA) to be used for phototherapeutic keratectomy (32) to reduce corneal scaring.

During the photorefractive keratectomy (PRK) procedure, the corneal epithelium is first removed either 

mechanically or with the excimer laser. After programming the amount of intended refractive change required 

and baseline eye examination data, a computer-assisted 

algorithm determines the excimer treatment parameters.

The laser is then used to reshape the anterior curvature 

by removing basement membrane, Bowman’s membrane, 

and portions of the corneal stroma (33) (Figure 6). In 

October 1995, the FDA approved the use of the excimer 

laser to perform PRK (34). Initial approval was granted 

for the correction of low-to-moderate levels of myopia 

(34). As more information became available, approval 

was also given to correct higher levels of myopia (35), 

astigmatism (36), and low-to-moderate levels of hyperopia 

(37,38) (Appendix B).

PRK is an outpatient procedure, requires only topical 

anesthesia, and takes about 10 minutes. The laser beam 

exposure time is dependent upon the amount of refractive 

error to be treated (average 30 seconds). After treatment, 

bandage contact lens(es) are placed on the eye(s) to assist 

in the healing process and to reduce pain. Treated eye(s) 

are often painful 1 to 2 hours postoperative and become 

increasingly painful during the first 8 to 12 hours. By 

the following day, the pain is reduced considerably, and 

Figure 5. Radial Keratotomy (RK) the cornea is reepithelialized in most patients within 48 

Figure 6. Photorefractive Keratectomy (PRK)
4

hours. Vision is usually considerably improved within 3 

to 4 days, and most patients become slightly overcorrected 

for a few weeks before stabilizing. Refractive corrections 

stabilize within 3 to 6 months for lower amounts of correction but may take 6 to 18 months for higher amounts 

of correction (39,40).

During the evolution of PRK, the ablation zone diameter progressively increased from 3.5 millimeters (mm) 

to 6.5 mm or more (41). Patients with smaller ablation 

zones reported a higher incidence of symptomatic halos 

under night-driving conditions (42,43). The larger optical zone reduced the effect of optical irregularities at the 

junction of the ablation zone and the untreated cornea, 

which is thought to cause symptomatic halos (44). (Note: 

78% of patients with ablation zones of ≤ 5.00 mm reported seeing halos at night (45,46).) Larger ablation 

zones (≥ 6 mm) had less critical centering requirements 

when used for mild-to-moderate refractive corrections 

(45,47). However, when larger ablation zones are used 

for higher corrections, centering is critical due to the 

steep and deep transition zone between the treated and 

untreated portions of the cornea (48). Precise centration 

of the laser over the pupil entrance is important, as clear, 

crisp vision depends upon the regularity and centration 

of the ablated optical zone. Initially, self-fixation by the 

patient was used, and there were reports of decentration 

occurring in about 20% of PRK treatments (49). Patients 

with decentered ablations have problems with monocular 

diplopia, glare, and irregular astigmatism (50,51). When 

this occurs, the most common option for correcting irregular astigmatism is a rigid contact lens. Thus, a patient 

who had previously been unable to wear contact lenses is 

at a greater risk for a decrease in best spectacle corrected 

visual acuity (BSCVA) (40,52).

While the epithelium has completely healed within 4 

to 5 days after surgery in most cases (53,54), epithelial 

wound healing has occurred as late as several months 

after surgery (48). Studies found that a smooth corneal 

surface at 1 to 3 months after surgery did not guarantee 

a smooth surface at 6 months, as the extent of deposition 

of new corneal tissue was unpredictable (55,56).

Table 1 presents a synopsis of clinical results for PRK.

Those percentages with standard deviation are the average taken from multiple studies. Those with no standard 

deviation are results from individual reports. A significant 

amount of data and information are available for lower 

amounts of myopia (< 6.00 D), while less data are available for higher amounts of myopia (>6.00 D) and for 

photoastigmatic keratectomy (PARK). (Note: PARK corrects for astigmatism and the combination of astigmatism 

with myopia or hyperopia.) Additionally, since FDA 

approval for the use of excimer lasers for the correction 

of hyperopia and hyperopic astigmatism occurred later, 

there is less long-term information regarding the efficacy 

and safety of hyperopic PRK and PARK. However, studies 

reported a slower recovery of uncorrected visual acuity 

(UCVA) and BSCVA for hyperopes, as compared with 

PRK and PARK for myopia (57).

PRK patients can develop dry-eye symptoms after 

surgery. One study, using the patient’s non-operated eye 

as a control, reported postoperative Schirmer test values 

and break up time (BUT) scores at 6 weeks. The values 

and scores for the PRK eyes were about half that of the 

non-operated eye, which resulted in dry-eye problems 

(110). Another study reported a decrease from mean 

preoperative Schirmer test values to those at 1 month 

postoperative after having PRK or PARK. At 6 months, 

mean values were still lower than preoperative values but 

had increased somewhat (111).

PRK has resulted in the development of corneal haze 

and regression (reverting to original state of refractive 

error). Studies have shown association with patient age 

(no significant difference at > 1 year) (112), biological 

risks (significantly increases in higher correction with 

small diameter ablation zone and ocular surface disorders, 

no gender differences except for females taking oral contraceptives [13.5X more likely to occur]), and environmental factors (increases with exposure to solar radiation, 

tanning beds). However, no association could be found 

with contact lens wear, swimming, cigarette smoking, or 

minor ocular trauma (113). Sharif et al. (114), reported 

on 9 bilateral patients (18 eyes) who became pregnant 

during the follow-up period and developed regression and 

corneal haze. Sixty-six percent of eyes (n=12) regressed 

and 83% (10/12) of these had regression associated with 

corneal haze (1+ to 2+ grade). Three patients (6 eyes) 

that had a stable refraction became pregnant at 5 months 

postoperative and developed corneal haze and associated 

myopic regression, which did improve in 50% of eyes 

after delivery (114).

The correlation between eye color and the development 

of corneal haze has been reported. In a study of 100 blue 

eyes of white patients and 166 brown eyes of Saudi patients 

with comparable range of myopia, 95% of the blue eyes 

were within ± 1.0 D of attempted correction compared, 

with 89% of the brown eyes at 6-months postoperative.

One hundred percent of the blue eyes achieved UCVA 

of 20/30 or better, compared with 92% of the brown 

eyes. Five percent of blue eyes developed corneal haze, 

compared with 29% of the brown eyes. Relative risk 

for developing haze was found to be 7.72X greater in 

brown eyes, suggesting that race might be a factor in the 

development of corneal haze (95).
5

Table 1. PRK percentages in this table are calculated from statistics referenced in this document. 30,38,40,44,45,57-109,133,143,184,199,200

Myopia Myopic Astigmatism Hyperopia Hyperopic Astigmatism 

Low Mod High Low Mod High Low High Low High 

< 6.0 D 6.0 – 10.0 D > 10. D < 1.00 1.25 – 2.50 D >2.75 d 3.00 D t 3.10 D < 1.75 t 1.75 

UCVA 20/40 or Better 93.3% 83.0% 60.3% 90.0% 92.9% 90.8% 88.3% 56.7% — — STDEV ± 7.7% ± 17.9% ± 23.6% ± 10.5% ± 9.8% ± 8.2% ± 27.6% 20/25 or Better 81.3% 70.4% 61.4% — 86.3% — 8.0% — — — STDEV ± 12.0% ± 29.7% ± 19.7% ± 4.2% 20/20 or better 62.5% 58.6% 26.9% — 82.3% 43.0% 76.0% 34.0% 85.5% 69.5% STDEV ± 18.2% ± 29.9% ± 5.4% ± 25.0% ± 21.3% ± 18.9% Emmetropia Within r 2.00 D — 87.5% 68.8% — — 92.5% — — — — STDEV ± 17.0% ± 8.5% Within r 1.00 D 78.5% 81.8% 57.1% — 70.7% 87.8% 85.2% 51.0% — — STDEV ± 11.3% ± 17.8% ± 15.2% ±17.3% ± 16.2% ± 6.6% ± 21.5% Within r 0.50 D 62.2% 57.7% 24.6% — 77.6% 69.8% 75.6% 27.8% 81.0% 56.1% STDEV ± 23.3% ± 19.5% ± 10.8% ± 4.9% ± 23.5% Loss BSCVA 1 line 0.7% 5.0% — — 0.51% 3.5% — 11.3% — — STDEV ± 3.9% ± 5.4% ± 5.2% 2 or more lines 3.0% 2.8% 15.1% — 4.7% 0.33% 2.4% 24.5% 2.6% 12.2% STDEV ± 3.4% ± 2.6% ± 4.9% ± 3.4% ± 15.9% Gain BSCVA 1 line — 30.1% — — — — — 7.1% — — STDEV 2 or more lines 18.6% 4.7% 3.6% — 0.5% — 3.4% 3.1% — — STDEV ± 2.5% ± 0.6% 
6

There have been reported problems with late-onset 

corneal haze (LOCH). Diagnostic criterion for LOCH is 

acute haze of grade ≥ 2 occurring between 4 and 12 months 

postoperative. One study, which followed 314 eyes for 12 

to 41 months, reported that 11 eyes developed LOCH after 

exposure to high levels of environmental UV-radiation (115).

The study suggests that the use of UV-protective eyewear 

should be encouraged during the first year after PRK. In 

another study that followed 1,000 patients for 12 months, all 

corneas were clear at 4 months, after 4 months, however, 18 

eyes of 17 patients developed LOCH, resulting in decreased 

visual acuity and regression. Treatment with topical steroids 

resulted in partial reversal of haze and regression. The study 

suggests that corneal healing and remodeling may continue 

for at least 1 year after PRK (116).

Compared with reports about RK, initial trials for 

PRK did not report significant problems with diurnal 

fluctuation of vision (121), progressive hyperopic shifts 

(37), reduced corneal strength (122), poor refractive 

predictability (74), and fluctuation of vision (121). However, long-term PRK studies have reported problems with 

glare (94,108,119,123), halos (108,124,125), regression 

(81,126), haze (44,65,98,108,109,112-116,127,128), 

decreased visual performance at night (119,129,130), 

undercorrection (81,131), overcorrection (130,132), loss 

of BSCVA (40,63,66,68,70,76,94,103,109,133,134), and 

severe dry eye problems (110,111,135-137). As a result of 

these reported problems and advances in laser refractive 

procedures, PRK has been all but replaced. A survey of 

refractive surgeons in the United States reported that the 

percentage performing PRK had decreased from 26% in 

1997 to less than 1% in 2002 (138). A list of patientreported satisfaction and complications after PRK surgery 

is summarized in Table 2.

Laser in situ Keratomileusis

Laser in situ Keratomileusis (LASIK) is a technique that 

uses the excimer laser and a specially designed knife blade 

called a microkeratome, which slices a thin, horizontal flap 

(100 to 200 μm in depth) off the top of the cornea leaving 

it connected by a small hinge of tissue (139) (Figure 7). The 

corneal flap is folded aside, and the excimer laser is used to 

remove tissue from the corneal stroma (Figure 8). The flap 

is then replaced. Many patients report seeing clearly immediately after surgery and have little or no discomfort.

LASIK was initially used to treat higher amounts of 

myopia. As surgeons increased their surgical skill, LASIK 

has become the surgery of choice and is now used to treat 

even low-to-moderate amounts of myopia, astigmatism, and 

hyperopia (Figure 9). Initially, refractive surgeons felt that 

there was no need for clinical trials and FDA approval, since 

LASIK is a procedure that uses 2 FDA-approved devices. In 

July 1997, the FDA approved the use of the excimer laser 

and the microkeratome for the LASIK procedure (140).

(Appendix B)

Table 2. Patient reported satisfaction and complications after PRK.

Myopic PRK Hyperopic PRK 

Reported Patient Satisfaction

Satisfied - very satisfied 70-92% 44,117-120 96-100% 90,91

Dissatisfied 3-20% 117,120

Quality of Life 

Improvement 78% 117

Decrease 17% 117

Correction Required After Surgery 

None 66-100% 117, 119

Sometimes worn 30% 119

Always worn 10% 119

Glare 

Daytime 55% 62,108,118 14-16% 90,91

Halos 

At night 7% 100

Always 34% 62,119 

Sometimes 26% 119

Never 40-79% 119

Night Vision Problems 

Always 32-40% 119

Sometimes 30% 119

Never 30% 119

Decreased night vision 32% 100,118

Increased difficulty driving at night 30-31%118 27-29% 90,91
7

Relative to PRK, LASIK patients experienced less pain, 

stabilized faster, had less regression, did not require extended use of topical steroids, and had fewer complications 

and side effects (141-143). However, unlike PRK, LASIK 

requires a greater surgical skill (144-146) and, therefore, 

does have a greater risk of surgical complications (147).

These risks include ocular perforation (141,148-150), 

button hole-flap (center of the flap is too thin resulting 

in a hole) (150,151), dislodged or detached corneal flap 

(141), and poorly aligned or positioned flap, resulting in 

irregular astigmatism (141). Postoperative LASIK risks 

include epithelial ingrowth (141), foreign bodies in the 

stromal bed (141), slower healing rate (141), microkeratome-induced subconjunctival hemorrhages (141) and 

infectious keratitis (152-154). In addition, there have 

been reports of microkeratome-induced complications 

of elevated intraocular pressure (IOP) (155) and retinal 

detachment (RD) (156,157).

Table 3 presents a synopsis of clinical results for LASIK 

referenced in this document. Percentages with standard 

deviation are the average taken from multiple studies.

Those with no standard deviation are results from a 

single clinical study. There is a significant amount of data 

for both low and high amounts of myopia and myopic 

astigmatism. Since approval for the use of excimer lasers 

for the correction of hyperopia and hyperopic astigmatism did not occur until November 1998, there is less 

long-term information regarding the efficacy and safety 

for LASIK for hyperopia and hyperopic astigmatism.

However, most studies reported that there is a slower 

recovery of BSCVA and UCVA with these procedures, 

as compared with myopic LASIK.

Symptoms of dry eye and recurrent corneal erosion 

syndrome are not uncommon after LASIK. According 

to a survey, 48% of patients complained of dryness 

symptoms, 6.7% complained of soreness of the eye to 

touch, 8% with sharp pains, and 5.6% of eyelids sticking to the eyeball (more common and severe with PRK 

than LASIK) (135). Patients in this survey reported a 

median overall satisfaction with surgery of 9 on a scale 

of 1 (worst) to 10 (best). Patients with 1 or more symptoms were twice as likely to have a satisfaction score < 8 

(135). Studies that reported a change in tear secretion 

and film instability from preoperative values to those at 

6-months postoperative found that Schirmer test values 

were approximately 24% lower, BUT scores were 19% 

lower, and change in tear osmolarity was 36% lower 

(136). A study by Aras et al. reported on the differences 

between operated and non-operated eyes of patients who 

had unilateral LASIK. Schirmer test and BUT values 

showed a decrease of 23% and 13% between operated 

and non-operated eyes, respectively (158).

Patient reports of satisfaction and complications after 

myopic LASIK are listed in Table 4. LASIK patient satisfaction scores are higher than those with PRK (Table 

2), and the percentage reporting problems with light 

sensitivity and night vision problems are less.

By 2001, more than 9.5 million LASIK procedures were 

performed worldwide and 5.1 million performed in the 

US (217). By 2003, the total number of LASIK procedures worldwide had increased to more than 15 million, 

and there are currently about 3,800 surgeons throughout 

the US performing more than 1 million new LASIK 

procedures each year (218,219). Reports of postoperative complaints have increased as more procedures have 

been performed and more long-term data have become 

available. Unfortunately, some of these complaints have 

been rather severe. These include: overcorrection (220-

222), undercorrection (160,187,223), loss of BSCVA 

(167,177,208), glare (224), halos (200), reduced visual 

performance in dim illumination (167,225), dry eyes 

(136,226,227), irregular astigmatism (226), and dislodged 

or detached corneal flap due to trauma occurring from 

6 weeks to 38 months postoperative (228-236). Even 

with this substantial list of postoperative complications, 

LASIK is still the surgery of choice by patients and refractive surgeons.

Figure 7. Microkeratome 

Cutting a Corneal Flap 

Figure 8. Excimer laser 

ablating tissue from corneal stroma during LASIK

Figure 9. After creation of the LASIK flap, the 

laser beam rotates around the central corneal 

tissue for hyperopic LASIK, creating a donut 

shape ablation and leaving the central area 

untouched
8

Table 3. Percentages in this table are calculated from statistics referenced in this document. 74,80,84,85,88,101,102,104,107,143,159,160-214

Myopia Myopic Astigmatism Hyperopia Hyperopic Astigmatism 

Low

< 6.0 D 

Mod

6.0 –10.0 D 

High

> 10.0 D

Low

< 1.0 D

Mod

1.0-2.5 D 

High

 2.75 D 

Low

 3.00 D 

Mod

3.10-5.00 D 

High

 5.10 D

Low

<1.0 D 

Mod

1.0-2.5 D

High

 2.75 D

UCVA 20/40 or Better 90.8% 69.3% 76.9% 93.4% 92.2% 82.2% 93.2% 88.9% 78.7% — 87.3% — STDEV ± 9.8% ± 25.2% ± 17.2% ± 13.9% ±10.0% ± 18.8% ± 5.5% ± 9.0% ± 9.0% ± 14.3% 20/25 or Better — 79.8% 47.5% 100% 84.8% 78.8% — — — — 67.5% — STDEV ± 0.9% ± 11.9% ±14.5% ± 7.5% 20/20 or better 68.6% 50.6% 39.5% 66.6% 65.2% 70.1% 29.7% 54.9% 32.2% — 24.7% — STDEV ± 12.3% ±24.2% ± 22.4% ± 31.0% ± 26.1% ± 5.3% ± 28.6% ± 10.9% ± 23.1% Emmetropia Within 2.00 D 100% 96.2% 82.1% — — 15.7% — 100% 87.0% — — — STDEV ± 24.5% Within 1.00 D 72.6% 50.9% 74.9% 92.8% 93.9% 82.7% 97.3% 86.4% 76.7% 100% 89.6% 79.2% STDEV ± 31.1% ± 31.6% ± 15.1% ± 13.1% ± 15.9% ± 20.0% ± 7.1% ± 15.4% ± 10.4% ± 6.5 Within 0.50 D 79.9% 70.8% 50.9% 83.1% 64.7% 82.2% 55.7% 64.2% 38.6% 56.1% 60.8% 30.8% STDEV ± 16.4% ± 22.7% ±17.4% ± 24.3% ±10.9% ± 8.9% ± 4.1% ± 14.3% 0.9% ± 7.6% ± 16.3% Loss BSCVA 1 line — 4.3% 14.6% 1.2% 1.2% 15.7% — 33.3% — — 2.3% — STDEV ± 7.8% ± 16.3% 2 or more lines 1.4% 3.4% 4.4% 3.9% 1.3% 3.3% 13.3% 3.8% 7.5% 2.9% 2.3% 15.4% STDEV ± 0.6% ± 6.6% ± 1.0% ± 2.5% ± 1.7% ± 3.6% ± 6.4% Gain BSCVA 1 line — 48.7% 5.6% — 23.3% — — — — — — — STDEV 2 or more lines — — — — 0.5% 3.9% 7.7% 5.6% — 8.6% 5.9% — STDEV ± 5.9% 
9

Laser Epithelial Keratomileusis

Laser epithelial keratomileusis (LASEK), which is also 

called Epithelial-LASIK, E-LASIK, and Epi-LASEK, 

was introduced in 1999 and is reported to combine the 

advantages and reduce the disadvantages of PRK and 

LASIK (237). During the LASEK procedure (Figure 10), 

a pre-incision of the corneal epithelium is performed with 

a special microtrephine (an instrument used to make a 

circular cut on the epithelium) with a 70-μm depth-calibrated blade. The microtrephine is designed to leave a 

hinge at the cornea’s 12-o’clock position. Two to 3 drops 

of 18 to 20% alcohol solution are instilled for 30 seconds 

to loosen the corneal epithelium from the basement membrane. The area is then dried, thoroughly washed with 

water, and dried again. (Note: Alcohol solution is applied 

for 30 to 40 seconds in younger men, postmenopausal 

women, and long-time contact lens users. Applications 

of longer than 40 seconds can decrease the elasticity of 

the epithelial flap.) The corneal epithelium is lifted at the 

pre-incision, and the epithelial flap is gently detached and 

folded up at the 12-o’clock position, leaving a smooth 

surface. After the ablation, the epithelial flap is carefully 

repositioned with a small spatula over the stroma. A soft 

contact lens is applied for 3 to 4 days to keep the flap in 

place. Postoperative antibiotic and cortisone treatments 

are administered for a few days. In 3-4 days, the epithelial 

layer is usually regenerated and intact (238). It is postulated that the epithelial flap protects the bare surface of 

the stroma and prevents the influx of inflammatory cells 

from the tears, thus reducing the inflammatory damage 

to the corneal stroma (237).

Many surgeons have experienced difficulties removing 

the corneal epithelium when performing LASEK and have 

had to revert to performing PRK. VisiJet Inc., of Irvine, 

CA, received FDA approval in September 2004, for the 

“EpiLift System,” which is used to separate corneal tissue 

during the LASEK procedure. The system separates the 

epithelium from Bowman’s membrane, and an epithelial 

Table 4. Patient reports of satisfaction and complications after myopic LASIK. 

Myopic LASIK 

Reasons for Having Surgery 

Improve UCVA 88% 167

Improve cosmesis 21% 167

Achieved goals for surgery 94% 167

Reported Patient Satisfaction With results

Satisfied - very satisfied 50-98% 162167,215,216

Dissatisfied 

Would have procedure again 97-99% 159,215,216

Improvement of Functional Vision 

Improvement 81-100% 167

Decrease — 

Correction Required After Surgery 

None 95-96% 215,216

Sometimes (for presbyopia) 25% 215

Always — 

Light Sensitivity 

Unchanged 73% 215

Worse 27% 215

Better 6% 215

Night Vision Problems 

Unchanged 76% 215

Worse 24% 215

Better 17% 215

Never — 

Decreased night vision 14-39 % 170,216

Increased difficulty driving at night 9% 167
10

sheet of consistent thickness is removed without damaging 

the membrane. After the laser ablates the stromal tissue, 

the epithelial sheet is replaced and a bandage contact 

lens is placed on the eye. This system allows the surgeon 

to perform LASEK without the problems that occurred 

with using alcohol to remove the epithelium.

Advantages of LASEK over PRK include the absence 

of severe postoperative pain, faster optical recovery, reduced risk of infection (237-239), and, if the creation of 

the epithelial flap is unsuccessful, the surgeon can easily 

revert to traditional PRK (237,240). In addition, LASEK 

may be the best choice for patients with low myopia, 

eliminates many of LASIK’s flap-related complications 

(237-239,241), and can be a viable option for those 

patients who previously were not good candidates for 

LASIK. This includes patients with high myopia and 

thin corneas (241), flat corneas that would limit the 

size of the treatment zone (242), basement membrane 

disease (242), severe neovascularization due to long-term 

contact lens wear (237), or those with professions (e.g., 

police officers, fire fighters, military personnel, aviators, 

and athletes) or lifestyles that increase the risk of trauma 

(238). In patients with small palpebral fissures or deep-set 

eyes, LASEK can be used to avoid lacerations of the eyelid 

margins or having to perform a lateral canthotomy (surgical division of the outer canthus) to adequately position 

the microkeratome (241). Patients with recurrent corneal 

erosions are poor LASIK candidates; however, LASEK 

not only can correct refractive error, it may provide a cure 

for recurrent erosions (241).

Disadvantages of LASEK include complexity of the 

surgical procedure (more than 50% of surgeons reported 

problems creating the flap) (240), increased expense of 

surgical instruments (237), and greater postoperative 

pain and a longer initial recovery time as compared to 

LASIK. Preliminary studies, however, report that there 

is less corneal haze than with PRK (238,239,242,243), 

which may be due to the protected epithelium that 

reduces the risk of necrosis of underlying corneal cells 

(244,245), and less loss of BSCVA (241). In addition, 

LASEK reportedly has prompt stabilization of the epithelial structure and with no overproduction of collagen 

fibers in the photoablation area of the anterior stroma 

during healing. This may reduce corneal haze and the 

possibility of corneal scarring (246). LASEK patients often 

achieve uncorrected visual acuity of 20/40 or better in 1 

week (237,238,241) and by 6 months more than 96% of 

patients achieved 20/40 or better correction (247,248).

After 1 year, LASEK patients had better BSCVA and less 

corneal haze compared to PRK patients (249).

LASEK appears to be safe and effective in treating a 

wide range of myopia and astigmatism. Some refractive 

surgeons perform a modified version called “Butterfly 

LASEK,” which removes the epithelium from Bowman’s 

membrane, proceeding from center to periphery. A special 

retractor is used to move the two flaps of loose epithelium 

toward the limbus. Ablation is performed as with regular 

LASEK. This procedure is thought to preserve the limbal 

connection of epithelial stem cells and limbal vascular 

connections, which may improve epithelial viability and 

results in faster postoperative recovery (243).

Currently, the use of the excimer laser for LASEK is not 

FDA-approved, so this is considered an “off-label” use 

of the laser. Refractive surgeons should not advertise this 

procedure unless they are enrolling subjects for a clinical trial. Although the number of LASEK procedures is 

small compared to LASIK, early results for this procedure 

are promising. Nevertheless, additional studies will be 

necessary before LASEK is widely accepted as a viable 

procedure among corneal surgeons.

Thermokeratoplasty

Thermokeratoplasty uses heat to alter the properties 

and structure of corneal stromal collagen in order to 

modify the cornea’s anterior curvature. In 1898, Lans 

first demonstrated the ability to shrink tissue and change 

the cornea’s refractive power. In the 1970s, Gasser and 

Fyodorov refined this procedure. Termed “radial thermokeratoplasty,” the procedure corrected hyperopia by 

using a nichrome-tipped probe that was placed at a depth 

of 80% of the corneal stroma and heated to 600° C for 

0.3 seconds to shrink stromal collagen and flatten the 

peripheral cornea while steepening the central portion 

(250). Problems controlling the amount and depth of 

delivered heat resulted in unpredictable outcomes and 

Figure 10. Laser epithelial 

keratomileusis (LASEK)
11

refractive regression. Tissue necrosis resulted from high 

temperatures. There were also problems with epithelial 

thinning, recurrent corneal erosions, iritis, stromal melting, and loss of BSCVA (5).

Laser Thermal Keratoplasty (LTK) is a noninvasive 

procedure that uses laser light, which is absorbed by the 

cornea to produce the desired temperature elevations 

(251) (Figure 11). New advances in laser technology, 

a better understanding of corneal physiology, and the 

introduction of corneal topography analysis have led 

to the development of a safer and more effective LTK 

procedure. The patient’s preoperative refraction dictates 

the optical zone diameter and the number of laser spots 

used. A smaller optical zone (6mm) will result in a steeper 

cornea than a larger zone (7mm). Additionally, 8 laser 

spots are applied for corrections of +0.75 to +0.875 D, 

15 spots for +1.0 to +1.67 D, 24 spots for +1.75 to 2.25 

D, and 32 spots for +2.375 to +3.0 D (252).

In June 2000, the FDA approved the Hyperion LTK 

System, an infrared holmium-YAG laser, to treat patients 

who are farsighted (between +0.75 to +2.25 D, with or 

without astigmatism < 0.75 D), at least 40 years of age, 

and with a stable refraction (253). Contraindications for 

LTK include pregnant or nursing women, patients with an 

abnormal shape or thinning of the cornea, central corneal 

scarring, history of herpetic eye infection, an autoimmune 

or collagen vascular disease, clinically significant atopic 

syndrome (allergic), insulin-dependent diabetes, or a 

compromised immune system (253).

The Hyperion LTK System produces a non-visible 

laser beam that heats corneal tissue, causing it to shrink 

and tighten at the periphery, thus steepening the central 

area (254). Short-term studies have shown that, for most 

patients, LTK is temporary, since at 24 months postoperative a majority of patients have regressed to one-half 

of the correction observed at 6 months postoperative 

(253). While there seems to be less surgical complications 

with LTK, results and stability depend on the amount of 

correction attempted and the patient’s age (i.e., younger 

patients may have more regression) (253,255).

LTK is a relatively new procedure and, at this time, 

only short-term clinical study data have been published 

regarding its effectiveness and possible complications 

(256). This procedure is marketed as a treatment for older 

patients (≥ 40 years of age) who are mildly hyperopic (or 

early presbyopes) and are reluctant to have LASIK or PRK.

The procedure takes only a few seconds and is performed 

in the surgeon’s office. The major advantage for older 

presbyopic airmen is that LTK will reportedly allow them 

to see clearly at near and intermediate distances again.

With data that are currently available, it is impossible to 

determine how popular this procedure will become with 

airmen and what long-term complications may occur.

The FAA is currently approving on a case-by-case basis 

airmen who have had the LTK procedure. Airmen who 

have had the LTK procedure may be required to take a 

medical flight test. Upon passing the test, their medical 

certificate is issued under the “special issuance” section 

of part 67 (14 CFR § 67.401).

Conductive Keratoplasty

Conductive Keratoplasty (CK) is a procedure that reduces farsightedness. In April 2002, the FDA approved 

The ViewPointTM CK System (Refractec, Inc.), which 

uses radio frequency energy to gently heat and shrink 

corneal collagen tissue at specific treatment spots to create 

a band of tightening (Figure 12). This band reshapes and 

steepens the cornea to correct hyperopia (257) (Figure 

13). The procedure requires topical anesthetic, can be 

performed in-office, is minimally invasive, takes less than 

3 minutes to perform, has little postoperative discomfort, 

and features a rapid return to normal vision. CK is less 

invasive than LASIK surgery, as it does not require the 

creation of a corneal flap. As with LTK, a small optical 

zone results in a steeper cornea than a larger zone, and 

the number of treatment spots are titrated according to 

the degree of hyperopia to be corrected (252).

Figure 11. Laser Thermal Keratoplasty (LTK)

Figure 12. Conductive 

Keratoplasty (CK)
12

CK is recommended for patients who are mildly farsighted (+0.75 to 4.00 D with ≤ 0.75 D astigmatism), 

≥ 40 years of age, and have a stable refractive correction 

(258). Contraindications for CK include pregnant or 

nursing women, an abnormally shaped or thinning cornea, 

a history of herpes infection, severe dry eye condition, 

autoimmune disease, collagen vascular disease, significant allergies, insulin dependant diabetes, compromised 

immune status, nystagmus, and/or other conditions 

that prevent a steady gaze, or an implantable electrical 

device (e.g., pacemaker), which can be affected by radio 

frequency energy (257,259).

CK is being marketed as a procedure that meets the 

needs of patients that want a safe, less-invasive treatment 

for farsightedness. The procedure is considered to be 

temporary, as the amount of correction achieved at the 

time of the procedure normally decreases over time. Most 

patients may need to be retreated every 2 to 3 years, or at 

about the same frequency that they would have changed 

their reading correction (258). While uncorrected visual 

acuity is improved after CK, there may be a need for 

glasses or contact lenses to correct residual farsightedness 

or for reading glasses.

Preliminary data from 357 patients reported UCVA 

of 20/20 or better in more than 50% of patients, 20/25 

in 74% of patients, and 20/40 was achieved in 93% of 

patients (257,259,260). Less than 1% of patients lost 2 or 

more lines of BSCVA (257). At 9-months postoperative, 

the majority of the patients responded with no symptoms; 

others reported moderate to very severe problems with 

blurred vision, dryness, fluctuation of vision, glare, halos, 

light sensitivity, night driving vision problems, and variation of vision in bright light and dim light. While the 

majority (79%) was either “very satisfied” or “satisfied” 

with their results, 9% of patients were “dissatisfied” to 

“very dissatisfied” (257).

The safety and effectiveness of the View Point-CK 

System have not yet been established in eyes with diseases 

of the cornea (e.g., scar, or infection), previous surgery 

or injury to the cornea, previous intraocular or corneal 

surgery, a history of glaucoma, > 4.00 D of farsightedness, or > 0.75 D of astigmatism, or patients < 40 years 

of age (257). With clinical data that is available at this 

time, it is impossible to determine if CK will achieve 

the popularity of other refractive procedures. Longer 

studies are required to determine the significance to 

pilots of the reported problems with glare, halos, night 

vision problems, and variation of vision in dim light.

The FAA is currently approving airmen who have had 

the CK procedure on a case-by-case basis. At this time, 

airmen who have had the CK procedure may be required 

to take a medical flight test. Their medical certificate is

issued under the “special issuance” section of part 67 

(14 CFR § 67.401).

Intacs

Intrastromal Corneal Ring was a single ring segment 

used in the correction of mild nearsightedness, while 

Intacs uses 2 semicircular plastic inserts to correct refractive error. These plastic inserts are placed deep within the 

corneal tissue at the outer edge and away from the central 

optical zone (Figure 14). In addition, they can be removed 

and/or replaced with a thicker insert if greater correction 

is needed, with minimal risk (261). The FDA approved 

Intacs in 1999 for the correction of mild myopia (1.00 

to 3.00 D with ≤ 0.75 D of astigmatism). The procedure 

takes about 15 minutes and is done on an outpatient basis.

During surgery, a tunnel is created between the layers of 

the stroma, and the two crescent-shaped plastic inserts 

are placed in the tunnel. The thicker the ring, the more 

flattening and greater correction is achieved.

Intacs patients must be at least 21 years of age, have 

stable vision for at least 1 year prior to surgery, and healthy 

eyes with no disease or injury. Contraindications for Intacs include autoimmune or immunodeficiency diseases 

(e.g., lupus, rheumatoid arthritis, or AIDS), pregnancy 

or nursing, thin corneas, glaucoma, herpetic eye disease, 

ocular conditions that could increase the possibility of 

future complications (e.g., recurrent erosion syndrome, 

or corneal dystrophy), or taking prescriptions that may 

affect healing or visual acuity (262).

Figure 13. Steepening of the cornea to 

correct for hyperopia

Figure 14. IntacsTM semi-circular 

plastic inserts
13

With Intacs, more than 95% of patients saw 20/40 

or better; over 70% saw 20/20 or better, with no loss of 

BSCVA (263), normal contrast sensitivity (264), unaffected endothelial cell morphology (265,266), and stable 

diurnal vision (267).

One of the main advantages of Intacs is the explantation, or exchange of the inserts. When the implants 

were removed, there was a low complication rate and 

vision returned to preoperative measurements within 1 

to 11⁄2 months (268,269). When inserts were exchanged, 

the intended refractive correction was achieved within 

the first few days and remained stable (268). Some early 

postoperative complaints (mild-to-moderate pain, foreign 

body sensation, scratchiness, photophobia, glare, starbursts, halo, unstable visual acuity, or discomfort) have 

been reported, but most symptoms disappear within 6 

months postoperative (269,270,271).

As with all surgery, there is a risk of intraoperative and 

postoperative complications. Intraoperative complications include micro perforations from an incorrectly set 

scalpel, incisional gaps, poorly positioned inserts, and 

channel tunnel infections. The procedure is very demanding, and many surgeons have had difficulty in mastering 

it sufficiently enough to make it an effective alternative.

Postoperative complications include induced astigmatism, 

diplopia, subconjunctival hemorrhage, aqueous flare, 

stromal thinning, epithelial incision cysts, and epithelial 

plug. A diffuse haze in the stromal tunnel, medial and 

lateral to the segments may occur after surgery but gradually decreases over time. Lamellar channel deposits can 

develop within the first few months after surgery along 

the inner or outer curvature of the plastic insert. These 

become more prominent during the 12-month follow-up 

but have no clinical significance. An intraepithelial iron 

line central to the inner curvature has occurred in some 

eyes 6 to 9 months postoperative (271).

Intacs may be an alternative refractive procedure 

for patients who are seeking a long-term alternative to 

glasses or contact lenses but are uncomfortable with the 

irreversible changes to their vision from permanently 

altering the cornea. Studies have demonstrated the reversibility of the Intacs procedure, low intraoperative 

complication rates, and that most patients are satisfied 

with their results (271). Intacs are relatively new and 

the manufacturer has had a history of financial difficulties (272). However, Addition Technology Inc., Des 

Plaines, IL, has taken over the distribution of Intacs

and reported that, in 2002, there was an 87% increase 

in procedures over those performed in 2001 (272). Even 

with this increase in procedures, until the results of longterm studies are available it is difficult to determine if 

Intacs will achieve the popularity of other established 

refractive procedures.

Clear Lens Extraction

Clear lens extraction (CLE) is the removal of a noncataractous, crystalline lens of the eye with or without 

intraocular lens placement, to correct nearsightedness or 

farsightedness. The history of CLE dates back to 1708, 

when it was noted that after cataract operations some high 

myopic eyes had good vision without the use of spectacles.

It was noted, however, there was a 3- to 10-fold increase 

in the incidence of RD when compared with eyes that 

did not have the surgery (273).

CLE was almost completely abandoned due to risks of 

RD and blindness (273,274). However, within the last 20 

years there have been published case studies and editorials 

in ophthalmic journals on the risks and benefits of CLE.

It has become a viable procedure for myopia, hyperopia, 

and astigmatism due to advancements in phacoemulsification, viscoelastic materials, and intraocular lens designs 

that improve the safety and efficacy of cataract surgery 

and has led to more reproducible and stable refractive 

results (275).

CLE is usually reserved for high myopic eyes (>12 

D), for which LASIK or PRK may be contraindicated 

(276-278). It may be a better choice for patients with 

high hyperopia than those with myopia, because of the 

smaller risk of postoperative RD and there are fewer 

modalities available to treat high hyperopia (279,280).

Many surgeons are hesitant to endanger an eye or expose 

an otherwise healthy eye to undue risk, but with new 

technology there is an accuracy rate of approximately ± 

0.25 D, especially for high hyperopia and myopia.

With the recent advent of multifocal intraocular lenses 

(IOLs), CLE has been used to correct presbyopia. When 

an IOL is used in this manner, it is considered “off-label” 

since the FDA has not approved it to be used for refractive surgery purposes. Previously, patients undergoing 

cataract surgery had only a monofocal IOL option that 

allowed clear distant vision without glasses. For near and 

intermediate postoperative vision, patients had to rely 

on reading glasses. With multifocal and accommodating IOLs, they now may have clear uncorrected vision 

at distance, intermediate, and near. The only FDA-approved multifocal IOL is the Array®, which was approved 

in 1997. The Array® is a zonal progressive intraocular 

lens with 5 concentric zones on the anterior surface that 

work on the principle of simultaneously presenting images at different focal lengths to the retina (Figure 15). A 

study of the Array® lens reported that more than 80% of 

patients were able to see 20/40 or better at distance and 

Jaeger # 3 (20/40) or better at near, without correction 

and with high patient satisfaction (281,282). There was 

some concern with the Array® lens that there may be a 

loss of contrast sensitivity at low spatial frequencies and 

increased glare and halos around lights (281). However, 
14

studies showed no difference in low-contrast sensitivity 

between binocular Array® patients and binocular monofocal patients; the occurrence of ghosting and glare was 

similar in both the Array® and monofocal IOL groups 

(283-285). Additionally, when stereoacuity was compared 

in 31 patients with unilateral Array® lens implants to 29 

patients with bilateral Array® lens implants, results were 

similar for both groups (286). Another study, which 

measured night driving performance of patients with Array® IOLs to those with monofocal IOLs, under 3 poor 

visibility conditions, found that there was no difference 

in recognition rates and recognition distances for signs 

and hazards (287).

An accommodating IOL has a monofocal optic and 

special hinges at the optic-haptic junction, which move 

by contraction and relaxation of the ciliary muscle within 

the eye, resulting in a form of accommodation so that 

patients can see clearer at far, near, and intermediate distances (Figure 16). The CrystaLens®, which received FDA 

approval in 2003, is currently the only FDA-approved 

accommodating IOL. Clinical trial data reported, at 1-

year postoperative, that 98.4% of patients had 20/40 or 

better UCVA; 100% had BSCVA of 20/20; 100% had 

20/32 or better UCVA intermediate vision; 98.4% had 

J3 or better UCVA near vision; and 100% had BSCVA 

of 20/20 (288,289). It was also reported that the CrystaLens® performed equally compared to a monofocal lens in 

contrast sensitivity both with and without a glare source.

Currently, the FAA does not issue airmen a certificate if 

they have either a multifocal or accommodating IOL 

with CLE, since it does not have FDA approval and is 

considered an “off-label” use.

Clear lens extraction, however, appears to be one of 

the more stable refractive procedures available, with ± 

0.02 D/year refractive change reported over a 9-year 

observation period. Several studies have shown that, 

for quality of vision, an unaltered cornea is optically 

superior to an operated cornea. Optical aberrations can 

occur after any corneal procedure that creates abnormal 

contours and, with larger amounts of refractive correction, there is a decrease in the quality of vision in lowcontrast situations (e.g., driving at night). CLE, however, 

is not without complications, which can range from 

posterior capsular opacification (279,280), intraocular 

lens dislocation (291), macular edema (more common 

in hyperopes) (292), glaucoma (280,290,293), uveitis 

(273), endothelial loss (292,294), postoperative hypotony 

(295), to more serious ones that can result in blindness 

(e.g., RD, [275,276,278,290,291] or endophthalmitis 

[273,275]). Colin et al. (296), reported in an extended 

study that followed patients with high myopia and CLE 

for 4 years found that 2% of the patients had RD, but 

by 7 years that number had increased to 8.1%. Ramos 

et al. (297), in their review of literature, reported that 

there are several variables that have a significant affect 

on the rate of RD after cataract surgery, which included 

age, gender, refractive state, status of the fellow eye, and 

the condition of the posterior vitreous. Age was the most 

significant variable for RD (298-300). Patients whose age 

was less than 60 years had a RD rate of 2.43%, while 

those ages 60 to 69 had a rate of 1.51%, those ages 70 

to 79 had a rate of 0.82%, and those 80 and over had a 

rate of 0.47% (298). Results of CLE are encouraging; 

however, patients must be aware of the increased risk for 

severe vision loss (274).

NEW TECHNOLOGY

The knowledge gained from past and current refractive 

surgery techniques has led to new alternatives or considerations concerning the visual system. One important 

lesson learned is that 20/20 acuity is not the only means 

to measure good vision. Snellen 20/20 measures about 

80% of the total visual system of the human eye and 

is a low-order aberration (prism, sphere, and cylinder) 

or quantitative measures of central vision. The remaining 20% involves higher-order aberrations (qualitative 

measures).

Figure 16. CrystaLens® Accommodating IOL

Figure 15. Array® Multifocal IOL
15

Phakic Intraocular Lenses

Phakic intraocular lenses (IOLs) are synthetic lenses 

that are implanted into the eye as an addition to the 

eye’s crystalline lens. They can be used to correct extreme myopia or hyperopia and can be combined with 

LASIK to correct even greater refractive errors. During 

the procedure, a small incision (approximately 3-5 mm) 

is placed at the periphery of the cornea, and the IOL is 

inserted through the incision into the anterior chamber 

(Figure 17) or the posterior chamber just in front of the 

crystalline lens (301). An anterior chamber phakic IOL 

is secured into place on the iris with two small flexible 

hooks. A posterior chamber phakic IOL is placed behind 

the iris, in front of the crystalline lens, and centered with 

the pupil. Phakic IOLs do not interfere with accommodation of the crystalline lens (302).

Aphakic IOLs were first introduced in the 1950s, and 

the designs and materials have changed dramatically over 

the years. Whether used to correct aphakia or a high 

refractive error, IOLs are known for exact predictability, 

reproducibility of the surgical success, and reversibility 

of the procedure. One of the factors contributing to the 

safety of this procedure is that the intraocular anatomy 

or physiology of the eye is not changed (i.e., the central 

cornea is not touched during surgery). The lens can be 

removed or exchanged with no long-term effects (302).

There are only two phakic IOLs that have received 

FDA approval to be used for refractive surgery. They 

are the “Verisyse” (formally Ophtec’s ArtisanTM) from 

Optec/Advanced Medical Optics, which is an anterior 

chamber lens used to treat severe myopia and hyperopia, 

and the “Visian Implantable Contact Lens” (ICL)” from 

STAAR, which is a posterior chamber aphakic IOL now 

being marketed as a phakic IOL or ICL. Both lenses are 

intended for people with healthy eyes, stable vision, and 

with no more than 2.5 D of astigmatism.

Clinical studies with phakic IOLs have reported an increase in BSCVA (303,304), stable vision (305,306), and 

an improvement in the quality of vision (i.e., no change 

in vision when illumination varies; 307,308). As with all 

types of surgery, there is the possibility of complications, 

which include loss of endothelial cells (301,309-312), 

decentration of lens (121), pupillary block (313), RD 

(313,314), cataract formation (301,313,315,316), iris 

retraction or pupil ovalization (310,317,318), halo/glare 

(310,318,319), and a decrease in crystalline lens transmittance (311).

There are several other phakic IOLs seeking FDA 

approval. They include: “Veriflex Phakic IOL” from 

Optec/AMO, a foldable version of the Artisan/Verisyse 

phakic IOL; “AcrySof Phakic ACL” from Alcon; “Icare” 

from Cornéal, a one-piece foldable and injectable IOL 

made of a soft hydrophilic acrylic material; “Phakic Refractive Lens (PRL)” a posterior chamber lens made of a 

silicone material; and “GBR/Vivarte” from IOLTECH.

In Europe, these and other similar phakic IOLs have been 

in the hands of surgeons since as early as 1989. While 

this is a promising procedure for the correction of higher 

refractive errors, studies are needed to determine if the 

results will have long-term refractive stability without 

sight-threatening complications.

PRESBYOPIA SURGERY

Presbyopia eventually affects everyone. People often 

see presbyopia as a sign of advancing age and bifocals 

as a handicap. The presbyopic population in the United 

States is expected to double every 5 years until the year 

2010 (320,321). Presbyopia usually occurs around 40 

years of age. Aviators with presbyopia can experience 

problems reading maps, charts, or seeing the instrument 

panel. Approximately 56% of the civil airman population 

is ≥ 40 years of age. Many of these airmen are presbyopic 

and need correction for near and/or intermediate vision 

(322).

The long-established belief that presbyopia is caused 

by an age-related loss of elasticity or hardening of the 

crystalline lens has recently been challenged. Hardening 

of the lens and lens capsule does not appear to start in all 

individuals at the same time, nor does it progress at the 

same rate. Presbyopia, however, occurs at the same age, ± 

11⁄2 years, in 100% of the population (323). The ciliary 

muscles, crystalline lens, and zonules are the 3 primary 

components of the eye that provide accommodation. A 

new theory for the onset of presbyopia is that the lens 

continues to grow throughout life, while the eye, itself, 

stops growing after puberty. At approximately 40 years of 

age, the size of the crystalline lens begins to compromise 

Figure 17. An anterior chamber 

phakic IOL
16

the space of the lens-zonule-ciliary muscle complex. As 

the lens encroaches this area, the zonules become lax, 

and the force of the ciliary muscle contraction cannot 

be transmitted to the crystalline lens to allow the lens to 

change shape (321,323,324). This theory regarding the 

etiology of presbyopia has prompted refractive surgeons 

to conduct clinical studies on different methods for the 

surgical reversal of presbyopia, including Anterior Ciliary 

Sclerotomy (ACS), Laser Presbyopia Reversal (LAPR), 

and Surgical Reverse Presbyopia (SRP).

Anterior Ciliary Sclerotomy

Anterior Ciliary Sclerotomy (ACS) is based on the 

theory that stretching and enlarging of the globe over 

the ciliary body will alleviate crowding in the posterior 

chamber (325). The procedure involves the placing of 

shallow radial incisions in 4 quadrants of the conjunctiva, 

beginning at the limbus and carried back to the pars plana 

to avoid retinal complications (Figure 18). ACS provides 

more space for ciliary muscle contraction to force the 

vitreous forward, increasing focus power and providing 

accommodation.

ACS incisions were initially made outside the limbus, 

which resulted in regression during the healing process 

(325). Incisions were later made in the 4 oblique quadrants of the conjunctiva with the patient under topical 

anesthesia. Radial incisions, 3mm long and 600 μm 

deep, were made in each quadrant, spread apart manually 

with a specially designed forceps (Enhanced ACS). No 

sutures or cauterization were used in the incisions, and 

the conjunctiva was closed to prevent infection. While 

spreading the incisions initially enhanced the results, the 

effect again regressed to near preoperative levels due, in 

part, to wound contraction during healing.

The marked regression with the initial and enhanced 

ACS suggested that a plug was needed to keep the incision 

open. Silicone was used for the scleral expansion plug 

(SEP) because of its stability and that the plug could be 

shaped in the operating room. The dimensions of the SEP 

were 2.5 mm long, 0.6 mm high, and 0.6 mm wide. These 

measurements were calculated on the estimated incision 

length, depth, and the desired circumferential expansion 

of the sclera. The addition of the SEP blocked the wound 

closure and maintained the scleral expansion, resulting 

in a gain of accommodative amplitude (325).

The ACS procedure requires a great deal of surgical 

skill. Operative complications can include compromise 

of the limbal conjunctival barrier if the incisions are 

made too long or hemorrhage if the incisions are cut too 

deep (326), so the use of an ultrasonic biomicroscopy to 

measure scleral thickness is essential. In addition, if there 

is a posterior perforation in the ciliary body, there is a 

risk of RD, while an anterior perforation can result in 

a peripheral iris injury or prolapse (326). Postoperative 

complications include infection, ocular hypotension, and 

a myopic shift of 0.50 D to 2.00 D due to a reduction 

of the axial length.

A pilot study reported, at 6-months postoperative, the 

accommodative amplitude ranged from 1.9 D to 4.7 D, 

with a mean of 2.9 D, and the ability to read Jaeger J1 to 

J2 at near with distance correction. The surgery lowered 

intraocular pressure (IOP) by an average of 2 to 4 mm Hg.

Limbal perforation with an irregular pupil and perforation into the ciliary body requiring a suture occurred in 

only one case. There was neither visual loss nor infections 

reported. However, some patients did experience myopic 

shifts of 0.50 D to 1.00 D (321,327).

ACS is still investigational. The techniques need to be 

improved and standardized for consistent and reproducible results.

Laser Presbyopia Reversal

Laser Presbyopia Reversal (LAPR) is performed with 

the SurgiLight IR-3000 infrared laser (3 μm), which 

incorporates a beam-shaping delivery unit and scanning 

mechanism (328) (Figure 19). The conjunctiva is opened 

mechanically, and the laser is used to make 8 excisions 

in the sclera outside the optical zone in a spoke-like pattern. The excisions are approximately 2.5 mm long and 

400 to 500 μm deep, depending on limbal thickness 

measurements taken before surgery (329).

Regression does not occur with LAPR since the excisions 

do not close during the healing process. It is theorized 

that the troughs remaining after the laser excision become filled with subconjunctival tissue within 12 to 24 

hours, and this tissue is more flexible than the original 

scleral tissue.

Figure 18. Anterior sclerotomy involves making 

radial incisions into the sclera to expand the ciliary 

sulcus and increase the space for the crystalline 

lens to accommodate
17

The LAPR procedure offers a number of advantages.

Unlike other surgical presbyopia treatments, with LAPR 

there is no need for suturing any type of implants to the 

sclera, thus avoiding their potential complications or side 

effects. In addition, because the infrared laser partially 

coagulates blood vessels as it removes tissue, it makes a 

very clean excision of tissue.

Possible risks from LAPR include ocular hypotony, 

infection, and scleral perforation. Caution must be applied in cases of thin sclera. Since the conjunctival peritomy may cause subconjunctival hemorrhages, clinical 

researchers are evaluating a transconjunctival approach 

to minimize bleeding and shorten the procedure, which 

now takes approximately 30 minutes. In addition, since 

the sclera is weakened, studies will be required to determine whether this procedure places eyes at greater risk to 

rupture following blunt trauma. Furthermore, because the 

excisions are transparent and expose the bluish hue from 

the uvea, some patients may have a long-term cosmetic 

problem. The LAPR procedure may be contraindicated 

for patients with glaucoma, cataracts, uveitis, dry eyes, 

collagen vascular disease, and diabetes.

Patients (n=70 eyes) between the ages of 42 and 65 were 

treated in clinical trials in Venezuela and Argentina. LAPR 

was performed in 1 eye and repeated 1 to 4 months later in 

the second eye. Patients had near vision of J6 to J7 before 

surgery, but within 2 weeks after surgery, accommodation 

increased by 1 to 2.5 D, with further improvement within 

2 weeks to 2 months. Distance vision remained the same.

Although postoperative near vision ranged from J3 to J1, 

monocularly, when vision was tested binoculary visual 

acuity increased. Almost no visual regression occurred up 

to 18 months after surgery. There was reported foreignbody sensation and an increase in dryness for a few days 

after surgery. One patient described minimal distortion 

of vision on day 1 postoperative, but this cleared by day 

2. Some eyes remain red for about a month.

To date, most of the LAPR clinical trials have been 

obtained through small, private clinics outside the United 

States. Larger, controlled clinical trials are beginning in 

Europe. SurgiLight has received permission to patent this 

technology, and the first trials in the U.S. were cleared 

in January 2003 by the FDA under an Investigational 

Device Exemption (330).

Surgical Reverse Presbyopia

Surgical Reverse Presbyopia (SRP) is a new technique 

that allows the ciliary body to expand and stretch outwardly, increasing the distance between the lens equator 

and the ciliary muscle, which appears to restore accommodation (323) (Figure 20). The procedure is based on 

Schachar’s theory that accommodation decreases with age 

because the crystalline lens grows concentrically, decreasing the space between the ciliary body and the lens.

After several design changes, a technique was developed for the placement of 4 separate PMMA scleral 

expansion bands (SEB) into partial-thickness scleral 

tunnels (Figure 21). Each tunnel is located 3.50 mm 

posterior to the limbus in the oblique quadrants (323). 

A lamellar diamond knife creates the scleral tunnel 5.0 

mm in length and 150 μm in thickness. The SEB (4.0 

mm in length, 900 μm in width, 0.3 mm in depth) is 

inserted into the tunnel, with the 2 ends outside of the 

tunnel on the scleral surface.

Selection criteria for candidates for SRP are patients 

between the ages of 40 and 70 years, no refractive error 

Figure 19. SurgiLight IR-3000 Infrared 

Laser

Figure 20. Surgical Reversal of 

Presbyopia (SRP)

Figure 21. Insertion of scleral expansion 

bands (SEB)
18

at distance, and with binocular vision (i.e., vision in both 

eyes). Patients < 40 are considered if they are slightly 

hyperopia (< +1.00 D) and are having difficulty with 

near-work requirements (323).

Contraindications for SRP include prior cataract extraction, scleromalacia (degeneration or thinning of sclera), 

previous trabeculotomy, blood coagulation abnormalities 

(widespread blood clotting and/or profuse hemorrhaging), 

collagen-vascular diseases, developing cataract, and poorly 

controlled glaucoma. Relative contraindications include, 

monocularity, > 70 years of age, severe keratoconjunctivitis 

sicca, insulin dependant diabetes, and hyperopia > +1.00 

D (323). (Note: Candidates with these relative contraindications are evaluated on a case-by-case basis.)

In an initial study, preoperative eyes had an average of 2.1 

D of accommodation. One month after surgery, 9 patients 

had amplitude of accommodation ranging from 3.3 D 

to 5.5 D, with an average of 4.3 D. (Note: Interestingly, 

the fellow eye, which did not have the implantation, also 

gained amplitude after surgery, averaging 3.5 D.) It was 

postulated that this phenomenon was probably due to a 

central nervous system mechanism (321). Complications 

from the procedure have been minimal. One patient had 

conjunctival suture dehiscence (separation) that required 

a conjunctival graft and 5 patients had segment rotation.

Surgery with SEB appears to restore accommodation.

However, the procedure is still evolving and predictability 

needs improvement (321).

Currently, the FAA does not allow procedures such as 

ACS, LAPR, and SRP for the correction of presbyopia 

in civil airmen. These procedures are still in their investigational stages, and it is impossible to predict how these 

procedures might perform in an aviation environment.

Airmen should be cautioned against having any investigational procedure performed without understanding how it 

may affect their ability to receive a medical certificate.

WAVEFRONT TECHNOLOGY

Lasers used for refractive surgery have gone through 

several generations of upgrades. Wavefront technology is 

a term used to describe laser systems that can customize 

the IntraLASIK or LASIK procedures. While results have 

been good, and in some cases better than non-wavefront 

treatments for specific patients, not everyone qualifies for 

this approach because of FDA recommendations and the 

limitations of the technology.

A wavefront-guided system consists of 2 parts: a wavefront sensor and a programmed excimer laser, based on 

information from the sensor (331). The wavefront sensor 

system includes a fixation target, an input laser beam 

that generates a point light source, a wavefront sensor 

that measures the slope of the exiting wavefront, and 

software that will determine the characteristics of the 

ablation for the excimer laser. A visual fixation target 

assists the patient in maintaining view, direction, and 

accommodation during the wavefront measurement. As 

the patient fixates, a laser beam is directed into the eye 

that generates a point light source onto the retina. This 

light is reflected from the retina back through the pupil, 

and the wavefront of the light leaving the pupil is relayed 

to the wavefront sensor. The wavefront is distorted by the 

refractive properties in the ocular media. When the beam 

enters the eye, it has a flat wavefront, but after traveling 

through the cornea, crystalline lens, and the other ocular 

media, the flat wavefront becomes irregular and analysis 

reveals the aberrations of the optical system (331).

Conventional refractive surgery corrects 2 types of 

refractive error, spherical and cylindrical. Wavefrontguided refractive surgery creates treatments tailored to 

the individual eye based on the total wavefront error 

in patients’ eyes, rather than the conventional manifest 

refraction (331,332,333). It is thought that more than 

40% of eyes have higher order aberrations that are 0.25 

D or higher. If the pupil size is increased from 3 to 6 mm 

in diameter, this aberration can alter the spherocylindrical 

data by several diopters.

Once the wavefront map is known for low-order aberrations, how much tissue to ablate can then be calculated.

However, conversion of higher-order aberrations is more 

difficult. Based on the beam characteristics, energy per 

pulse, repetition rate, pulse size and pulse shape, and 

other factors, special algorithms can be generated for 

a treatment table that defines the location, size, and 

sequence of each laser.

There are several companies that produce lasers capable 

of performing wavefront guided treatments. These include 

VISX® CustomVue®, Bausch and Lomb® Zyoptix®, 

Alcon® CustomCornea®, and WaveLight Laser Technologie, Allegretto WaveTM. All of these systems have 

FDA approval.

The VISX® CustomVue® laser uses SmartBeamTM 

technology, which adjusts beam size and shapes ranging 

from 0.065 to 6.5 mm to allow for personalized refractive 

treatments. It also uses the ActiveTrakTM 3-D Active Eye 

Tracking that can capture all 3 dimensions of intra-operative eye movements without the requirement of pupillary 

dilation. The Variable Spot Scanning (VSSTM) technology 

adds a blend zone that increases the ablation zone by 

51%, increasing the overall diameter of the ablation to 8 

millimeters. This system is reported to remove minimal 

corneal tissue, have a shorter treatment time, and greater 

flexibility to personalize the laser treatment (334).

The Bausch and Lomb® Zyoptix® laser uses a 2 mm 

“flying spot beam.” Each spot ablates the corneal tissue 

in a pattern that allows the debris to clear in one place 
19

before contacting that area again. This allows each pulse 

to polish the corneal surface for a smoother result, and the 

scanner feedback mechanism ensures that every pulse is 

placed exactly as prescribed, with no laser beams fired at 

consecutive locations or overlap. No dilation is required, 

so there is quicker recovery time and less discomfort 

during the surgery with a maximum treatment area of 

up to 14 mm (335).

The Alcon® CustomCornea® uses the LADARVision® tracking system and the LADARVision 4000 laser 

system. The tracking device uses a closed-loop technology, 

which compensates for eye movements through continuous, constant feedback on the location of the eye (more 

than 4,000 times per second), telling the laser where the 

eye will be at the precise moment the laser is applied.

This system reshapes the cornea by correcting for both 

lower- and higher-order aberrations (336).

The Allegretto WaveTM laser (WaveLight Laser Technologie, Erlangen, Germany) features a spot 200Hz, 

Gaussian-shaped 0.95 mm flying spot, an active tracker 

with a response time of less than 6.0 milliseconds, does 

not require dilation of the eyes, and can be used for the 

treatment of both hyperopia and myopia. At 1-year 

postoperative, results from the FDA Allegretto myopia 

study treated for up to -12 D of myopia and 6.0 D of 

astigmatism reported that 85% of eyes were within ± 0.5 

D of target range, and more than half of the eyes (56%) 

achieved UCVA of 20/16. Even the high myopes did well 

with 80% of those eyes, with > - 7.0 D within ± 0.5 D 

of target range, compared to 86% of those with < - 7.0 

D. Of those with > - 7.0 D of myopia, 80% achieved 

UCVA of 20/20 or better, while 89% of those with < 

-7.0 D attained the same results. Only 0.6% lost 2 or 

more lines of BSCVA, while more than 58% gained 

1 or more lines. Patients in the trials were asked how 

much glare they experienced from bright lights (e.g., 

headlights, and/or streetlights) before and after LASIK.

There was an overall improvement in nighttime visual 

function and night driving (337). Investigators believe 

that this technology delivers excellent refractive results, 

with no spherical aberrations and a larger optical zone.

By preserving the optical zone size and better shaping of 

the ablation profile, nighttime visual function improved 

(338,339). The Allegretto laser has been used worldwide 

for several years and has been FDA approved in the USA 

since late 2003.

Wavefront-guided technology, along with improved 

microkeratomes, better eye tracking with the laser, and 

more precise information from the aberrometer to the 

laser is reported to improve outcomes and decrease 

the need for enhancement procedures. Some optical 

aberrations, however, will still be present because laser 

ablation always induces new errors. Currently, wavefront 

technology is recommended for those patients with pupil 

diameter greater than 6.6 mm, require optimum night 

vision, have higher prescriptions, and a large number of 

higher-order aberrations. This new technology comes at 

higher cost. Wavefront technology can add $100 to $400 

per eye to the cost. Patients for which custom wavefront 

LASIK is either unnecessary or unsuitable include those 

with refractive error outside the FDA-approval range, 

thin corneas, pupil diameters less than 5 mm, and a 

large disparity between the manifest refraction and the 

wavefront aberrometer-derived refraction (340). There 

is limited data from wavefront technology that can be 

compared with standard LASIK data (340). One comparative study of 12 patients with standard LASIK in 1 eye 

and wavefront LASIK in the contralateral eye reported 

at 6 months postoperative an UCVA of 20/40 or better 

in 100% of eyes in both groups and 20/20 UCVA in 

67% (8 eyes) with wavefront and 83% (10 eyes) with 

standard LASIK (341). Kaiserman et al. (342), reported 

that at 1 month after surgery UCVA of 20/20 or better 

was achieved by 72% of those with wavefront LASIK 

and 70% of those with standard LASIK. However, 88% 

of those with wavefront LASIK and only 40% of those 

with standard LASIK had improved contrast sensitivity 

measurements at one-month postoperative (342). It will 

be interesting to see how this technology performs after 

more long-term clinical data become available.

FEMTOSECOND LASER

Complications associated with LASIK are often related 

to the use of mechanical microkeratomes (343,344). Microkeratomes have a cutting accuracy of approximately ± 

60μm. A microkeratome set to cut an 180μm flap could 

produce a flap of 120μm to 240μm, which could prove 

unacceptable if large amounts of tissue are to be removed 

to correct high myopia. In addition, mechanical microkeratomes do not cut a perfectly planar flap. Often a flap 

is cut that varies in thickness between the peripheral and 

central areas. This can result in thin or irregular flap and 

induce astigmatism.

The FDA has approved the IntraLase femtosecond 

(FS) laser keratome, which has several advantages over a 

mechanical microkeratome. The laser keratome uses a spot 

size of about 3 μm creating the flap by placing tiny bursts 

of energy at a prescribed depth in the stroma (Figure 22).

Because this laser is computer-controlled, the surgeon can 

cut flaps as thin as 100μm with an accuracy of ± 5μm, 

leaving more tissue to be photoablated for higher corrections (345-347). There have been no reported partial or 

buttonhole flaps, epithelial sloughs, or free caps to date 

(345,347,348). Additionally, it has been reported that no 

procedures have had to be aborted due to loss of suction, 
20

as sometimes happens with mechanical microkeratomes 

(345). The surgeon has the ability to customize the flap’s 

thickness or hinge location and can change the edge angle 

to various degrees to eliminate the risk of epithelial ingrowth, thereby providing greater flexibility than can be 

attained with mechanical microkeratomes (345-347). It 

has been reported that surgically induced astigmatism in 

spherical corrections was significantly less with the IntraLase (346). There were also decreased epithelial injuries 

(345) and a reported shorter learning curve compared 

to mechanical microkeratomes (345).

There are disadvantages to this new technology. It 

takes about 45 to 50 seconds to create a flap with the 

FS laser keratome, as opposed to 10 to 12 seconds with 

a mechanical keratome. Some patients may require an 

additional 10- to 15-minute delay for the opaque gas 

bubbles that form to dissipate before lifting the flap for 

treatment (345). Surgical time is increased, leaving the 

stroma exposed for a longer period, which has resulted 

in some patients complaining of photophobia following surgery. Postoperative care is the same as used with 

mechanical microkeratome flap, as is visual recovery. The 

only visible difference is the appearance of the flap over 

time. Flaps created with the FS laser keratome have very 

well-defined borders, and the outline of the flap is much 

easier to see than the borders created with the mechanical 

microkeratome (345).

Future applications for the FS laser may include intrastromal photoablation. Intrastromal ablation could 

induce refractive change without cutting a flap, i.e., the 

laser would vaporize tissue to leave a cavity. With minimal 

damage to the cornea, the computer would put several 

cavities together in a line and in layers. Theoretically, 

once the cavity is created within the cornea, the cornea 

will change shape. A cavity in the central cornea would 

produce a myopic correction, while one in the periphery 

would correct hyperopia. In addition, clinical trials are 

using the FS laser to cut the channels necessary to insert 

intracorneal rings, so this refractive procedure may once 

again become an option for patients (345,348).

Inlays and Onlays

An alternative to removing corneal tissue is the development of a synthetic material that mimics the cornea’s 

collagen, which can be added to the cornea. An onlay 

made of a biocompatible polymer is cemented to an area 

of the cornea where the epithelium has been removed.

Epithelial cells regenerate and cover the onlay (Figure 

23). Research has indicated that a collagen Type I, coated 

polymer material mimics the basement membrane of 

the corneal epithelium and promotes the most favorable 

growth of epithelial cells in vitro, in comparison to wholly 

biological or other synthetic materials (349).

Researchers from Australia and Finland have implanted 

onlays on feline corneas and found that epithelial growth 

began on postoperative days 1 and 2 and were fully 

epithelialized by 5-11 days. The corneas remained clear, 

and histological studies showed that the onlays were 

well tolerated (351,352). Another possibility is to cut a 

flap, insert the same synthetic material used for onlays 

in the stromal bed, and then replace the flap (i.e., inlay 

procedure) (Figure 24). This procedure may present a 

greater challenge, and duplicates of some of the problems 

encountered with the flap used for LASIK.

Figure 22. IntraLase FS Laser 

Keratome procedure

Figure 23. Placement of corneal onlay
21

AEROMEDICAL ISSUES

Civil airmen with RK procedures were initially allowed to obtain FAA medical certificates through a 

waiver process. Airmen were to discontinue flying for 6 

months after having RK and then were required to apply 

for a new certificate. At the time of their examination, 

they were required to submit a “Report of Eye Evaluation” (FAA Form 8500-7), completed by their eyecare 

specialist verifying that healing was complete, vision was 

stable, and they met the vision standards for the applied 

certificate class. A follow-up eye evaluation report was 

required 6 months after an airman medical certificate was 

issued. To expedite tracking of this procedure, in 1983 

the FAA’s Aerospace Medical Certification Division assigned RK its own pathology code (130). This code was 

placed on the medical records of all airmen with RK.

By the early 1990s, applicants with RK could obtain a 

medical certificate without a waiver by passing the visual 

acuity standards for their class of medical certificate. Airmen who had a current medical certificate and had RK 

performed were to discontinue flying until an eye care 

specialist verified that their vision was stable and they 

had been released (352). An eye evaluation report (FAA 

Form 8500-7), completed by the surgeon who performed 

the procedure or another eye care specialist familiar with 

the applicant’s ophthalmological history, was submitted 

to the FAA verifying that the airman could meet these 

conditions and return to flying. If an airman with RK 

had not submitted a previous eye evaluation report, one 

was required at the time of certification renewal.

Although the FDA did not approve the first excimer laser 

for use in the US until October 1995, applicants with PRK 

applied for and received FAA medical certificates prior 

to that date. These airmen had gone to foreign countries 

for this procedure or were in the original investigational 

studies. Additionally, when surgeons changed to primarily 

performing LASIK, applicants applied for and routinely 

received their medical certificates. No waiver process is 

currently required for airmen with PRK or LASIK for them 

to receive a medical certificate. The present regulation for 

airman applicants with refractive surgery states:

An applicant who has been treated with refractive surgery may be issued a medical certificate by the Aviation 

Medical Examiner (AME) if the applicant meets the 

visual acuity standard and the “Report of Eye Evaluation” 

indicates that healing is complete, visual acuity remains 

stable, and the applicant does not suffer from significant 

glare intolerance. This state of recovery is usually reached 

within 6- to 12-weeks after surgery (352).

A study of civil airmen with refractive surgery reported 

an increase of approximately 37% in the number of such 

airmen between the periods of 1994-1996 to 1997-1998.

In addition, there was a change in the distribution of the 

types of refractive surgery procedures. While the largest 

number of civil airmen had RK, that percentage had 

decreased and the percentage of airmen with LASIK 

procedures had more than tripled (Figure 25) (353).

A later study of civil airmen with refractive surgery 

looked at the total civil airman population for the years 

1996 to 2001 (Figure 26). The results of this study reaffirmed those of the previous study. A greater number of 

civil airmen had LASIK (61%); while the prevalence of RK 

decreased to 24%. Interestingly, PRK has decreased from 

10% to 5%. This information confirms that civil airmen 

are continuing to have refractive surgery performed and 

suggests that they do not see it as a hindrance to flying 

or in obtaining an airman medical certificate.

SUMMARY AND DISCUSSION

During the last decade, there have been several new 

procedures introduced to reduce refractive errors, making it possible to see without contact lenses or glasses.

Procedures for hyperopia, myopia, astigmatism, and now, 

presbyopia, are being performed in increasing numbers.

RK, which was introduced in the late 1970s and gained 

widespread popularity, has been replaced by other procedures due to reported patient dissatisfaction and many 

short- and long-term complications. Long-term prospective evaluations of RK reported that there is a continuation 

Figure 24. Inlay procedure
22

of progressive hyperopic shifts and reduction of corneal 

strength (Note: Ruptures at the incision sites have been 

reported more than 10 years after surgery [10-13]). Even 

more worrisome in the aviation environment are diurnal 

fluctuations of vision of more than 1.50 D and altitudeinduced corneal changes (14-19).

After extensive investigational trials, in 1995 the FDA 

approved the excimer laser for PRK refractive surgery.

There was, however, reported patient dissatisfaction with 

postoperative pain, long recovery time, and refractive regression. In addition, early treatments had problems with 

haze, halos/glare, decreased visual performance at night, 

and dry eye problems, which raised concerns regarding 

PRK in the aviation environment. Due to these problems 

with PRK, refractive surgeons developed LASIK, which 

quickly became the surgery of choice. LASIK requires more 

surgical skill with the addition of the microkeratome to 

cut the corneal flap. Since there were no investigational 

studies prior to surgeons routinely performing LASIK, 

there were no clinical data regarding the possibility of 

operative and postoperative complications. Some surgeons, remembering the long-term, postoperative problems with RK, cautioned against the use of LASIK until 

more long-term clinical data became available. However, 

as of June 2002, there have been more than 9.5 million 

LASIK procedures performed and, of those, more than 

5.1 million were performed in the U.S. Information is 

now being published with increasing frequency, some 

reporting long-term and rather severe complications.

Many of the complications (e.g., under/over correction, 

loss of BSCVA, glare/halos, reduced visual performance in 

dim illumination, severe dry eyes, dislodged, or detached 

corneal flap up to 38 months postoperative) have raised 

concerns regarding the use of LASIK in the aviation 

environment.

The scientific evolution in adaptive optics shows that 

the human eye can achieve visual acuity of better than 

20/15 with improved image quality. The application of 

adaptive optics has added to our knowledge about vision 

and has led to advances in diagnostic technology. New 

refractive alternatives will need to effectively correct 

lower-order aberrations while inducing fewer higherorder ones. New refractive techniques will need to have 

4 critical ingredients: be safe and effective, maintain an 

aspheric cornea, minimize insult to the visual axis, and 

minimize tissue loss.

Optimum vision is essential for pilots who must detect 

and identify airborne traffic as well as hazards that may be 

on the runways or taxi lanes. Cockpit instrumentation and 

printed materials (e.g., charts, maps, and flight manifests) 

must be clearly visible to ensure that proper flight procedures and safety are maintained. It is unknown at this 

time how the long-term effects of refractive surgery may 

affect the performance of civil airman and if the known 

refractive surgery complications summarized in this paper 

may be exacerbated by age. It is important that pilots be 

aware of possible problems that may result from having 

refractive surgery that may affect their ability to safely 

perform aviation tasks. The news media and advertisers continues to promote the benefits of laser refractive 

surgery and often fail to report on patients who have 

Figure 25. Refractive surgery, by type, in civil airmen

Figure 26. Refractive surgery by type 

in civil airmen
23

less than ideal outcomes. There are sites on the Internet 

where refractive surgery patients whose procedure resulted 

in less-than-perfect results can voice their concerns and 

organize support groups in their area (354). To provide 

the aviation community with information to formulate 

administrative decisions and policies associated with 

both current and new refractive surgical procedures and 

techniques, continued monitoring of current refractive 

surgical procedures and clinical results of new refractive 

surgery techniques are required.

REFERENCES

1. Vision Channel, Refractive Errors. At URL: www.visionchannel.net/refractiveerrors/ (Accessed 1/03).

2. American Optometric Association. At URL: www.

aoanet.org/conditions/facts_stats.asp. (Accessed 

1/03).

3. Nakagawara VB, Wood KJ. The Aeromedical 

certification of photorefractive keratectomy in 

civil aviation: A reference guide. Washington DC: 

Department of Transportation/Federal Aviation 

Administration. 1998. Report No. DOT/FAA/AM98/25.

4. Stein HA, Slatt BJ, Stein RM. Refractive errors and 

how to correct them. In: Stein HA, Slatt BJ, Stein 

RM, eds. The Ophthalmic Assistant. St. Louis, MO: 

The CV Mosby Company; 1988:211-35.

5. Allard R. Corneal refractive surgery: Part I - past 

and present.Contact Lens Spectr. Aug 1991; 5(8):44-

50.

6. Waring GO 3rd, Lynn MJ, Nizam A, Kutner MH, 

et al. Results of the prospective evaluation of radial 

keratotomy (PERK) Study five years after surgery.

The Perk Study Group. Ophthalmol. Aug 1991; 

98(8):1164-76.

7. Waring GO 3rd, Lynn MJ, McDonnell PJ, PERK 

Study Group. Results of the prospective evaluation 

of radial keratotomy (PERK) study 10 years after 

surgery.Arch Ophthalmol. Oct 1994; 112(10):1298-

1308.

8. Werblin TP, Stafford GM. Hyperopic shift after 

refractive keratotomy using the Casebeer System.

J Cataract Refract Surg. Oct 1996; 22(8):1030-6.

9. Deitz MR, Sanders DR, Raanan MG, LeLuca M.

Long-term (5- to 12-year) follow-up of metal-blade 

radial keratotomy procedures. Arch Ophthalmol.

May 1994; 112(5):614-20.

10. Panda A, Sharma N, Kumar A. Ruptured globe 10 

years after radial keratotomy.J Refract Surg. Jan-Feb 

1999; 15(1):64-5.

11. Glasgow BJ, Brown HH, Aizuss DH, Mondino 

BJ, et al. Traumatic dehiscence of incisions seven 

years after radial keratotomy. Am J Ophthalmol.

Dec 1988; 106(6):703-7.

12. Lee BL, Manche EE, Glasgow BJ. Rupture of radial 

and arcuate keratotomy scars by blunt trauma 91 

months after incisional keratotomy. Am J Ophthalmol. Jul 1995; 121(1):108-10.

13. Goldberg MA, Valluri S, Pepose JS. Air bag-related 

corneal rupture after radial keratotomy. Am J Ophthalmol. Dec 1995; 120(6):800-2.

14. Anonymous. Radial keratotomy for myopia: American Academy of Ophthalmology. [see comments] 

[Review] Ophthalmol. Jul 1993; 100(7):1103-15.

15. Wyzinski P. Daily refractive changes persisting after 

radial keratotomy. Am J Ophthalmol. Aug 1989; 

108(2):205-6.

16. Wyzinski P, O’Dell LW. Diurnal cycle of refraction 

after radial keratotomy. Ophthalmol. Feb 1987; 

94(2):120-4.

17. Santos VR, Waring GO 3d, Lynn MJ, Schanzlin 

DJ, et al. Morning-to-evening change in refraction, 

corneal curvature, and visual acuity 2 to 4 years after 

radial keratotomy in the PERK Study. [see comments] Ophthalmol. Nov 1988; 95(11):1487-93.

18. McDonnell PJ, Nizam A, Lynn MJ, Waring GO 

3rd. Morning-to-evening change in refraction, 

corneal curvature, and visual acuity 11 years after 

radial keratotomy in the prospective evaluation of 

radial keratotomy study. Ophthalmol. Feb 1996; 

103(2):233-9.

19. Bullimore MA, Sheedy JE, Owen D, Refractive 

Surgery Study Group. Diurnal visual changes in 

radial keratotomy: Implications for visual standards.

Optom Vis Sci. 1994; 71(8):516-21.

20. Waring GO 3rd, Casebeer JC, Dru RM. One-year 

results of a prospective multicenter study of the 

Casebeer system of refractive keratotomy. Casebeer Chiron Study Group. Ophthalmol. Sep 1996; 

103(9):1337-47.

21. Grimmett MR, Holland EJ. Complications of 

small clear-zone radial keratotomy. Ophthalmol.

Sep 1996; 103(9):1348-56.
24

22. Tinning S. Contrast sensitivity and glare following 

keratotomy. AGARD Conference Proceedings No 

492. 1991; AD-A237 593.

23. Diamond S. Present status of radial keratotomy 

myopia surgery: aerospace considerations. Aviat 

Space Environ Med. Aug 1990; 61(8):732-4.

24. Waring GO 3d, Lynn MJ, Fielding B, Asbell PA, 

et al. Results of the prospective evaluation of radial 

keratotomy (PERK) Study 4 years after surgery 

for myopia. [see comments] JAMA. Feb 23 1990; 

263(8):1083-91.

25. Stulting AA. Radial keratotomy in perspective.

[Review] [Afrikaans] S Afr Med J. Apr 1988; 

73(7):417-21.

26. Creel DJ, Crandall AS, Swartz M. Hyperopic shift 

induced by high altitude after radial keratotomy. J 

Refract Surg. Jul-Aug 1997; 13(4):398-400.

27. Mader TH, White LJ. Refractive changes at extreme 

altitude after radial keratotomy. Am J Ophthalmol.

Jun 1995; 119(6):733-7.

28. Mader TH, Shallhorn SC, Blanton CL, Bilber B, 

et al. Refractive changes during prolonged exposure 

to altitude following refractive surgery. Oct 1994; 

MIPR NO: 94MM4576.

29. White LJ, Mader TH. Refractive changes with 

increasing altitude after radial keratotomy. [letter] 

Am J Ophthalmol. Jun 1993; 115(6):821-3.

30. Aron-Rosa DS, Boulnoy JL, Carre F, Delacour J, et 

al. Excimer laser surgery of the cornea: Qualitative 

and quantitative aspects of photoablation according 

to the energy density. J Cataract Refract Surg. Jan 

1986; 12(1):27-33.

31. Trokel S. Evolution of excimer laser corneal surgery 

[see comments]. J Cataract Refract Surg. Jul 1989; 

15(4):373-83.

32. Hersh PS, Spinak A, Garrana R, Mayers M. Phototherapeutic keratectomy: strategies and results in 

12 eyes. Refract Corneal Surg. Mar-Apr 1993; 9(2 

Suppl):S90-S95.

33. Fantes FE, Waring GO 3d. Effect of excimer laser 

radiant exposure on uniformity of ablated corneal 

surface. Lasers Surg Med. 1989; 9(6):533-42.

34. Editor. Summit PRK laser conditionally okayed by 

FDA panel.AOA News. Nov 1, 1994. 33(9):1&12-

13.

35. Dausch D, Klein R, Schroder E, Dausch B. Excimer 

laser photorefractive keratectomy with tapered 

transition zone for high myopia. A preliminary 

report of six cases.J Cataract Refract Surg. Sep 1993; 

19(5):590-4.

36. Editor. Lasers proving useful in treating astigmatism.

AOA News. Jun 1, 1992; 30(23):5&8.

37. O’Brart DP, Stephenson CG, Oliver K, Marshall 

J. Excimer laser photorefractive keratectomy for 

the correction of hyperopia using an erodible 

mask and axicon system. Ophthalmol. Nov 1997; 

104(11):1959-70.

38. Jackson WB, Mintsioulis G, Agapitos PJ, Casson 

EJ. Excimer laser photorefractive keratectomy for 

low hyperopia: Safety and efficacy.J Cataract Refract 

Surg. May 1997; 23(4):480-7.

39. Sher NA, Hardten DR, Fundingsland B, DeMarch 

J, et al. 193-nm excimer photorefractive keratectomy in high myopia. Ophthalmol. Sep 1994; 

101(9):1575-82.

40. Epstein D, Faterholm P, Hamberg-Nyström H, 

Tengroth B. Twenty-four-month follow-up of excimer laser photorefractive keratectomy for myopia, 

refractive and visual acuity results. Ophthalmol. Sep 

1994; 101(9):1558-64.

41. Seiler T, Kahle G, Kriegerowski M. Excimer laser 

(193-nm) myopic keratomileusis in sighted and 

blind human eyes. Refract Corneal Surg. Sep-Oct 

1990; 6(5):165-73.

42. Fichte CM, Bell AM. Ongoing results of excimer 

laser photorefractive keratectomy for myopia: subjective patient impressions. J Cataract Refract Surg.

Mar 1994; 20(2): 268-70.

43. Pallikaris IG, Lambropoulos IE, Kolydas PK, 

Nicolopoulos NS, et al. Excimer laser photorefractive keratectomy for myopia: clinical results in 96 

eyes.Refract Corneal Surg. Mar-Apr 1993; 9(Suppl):

S101-02.

44. Shah SI, Hersh PS. Photorefractive keratectomy 

for myopia with a 6-mm beam diameter. J Refract 

Surg. Mar-Apr 1996; 12(2): 341-6.

45. Tengroth B, Epstein D, Fagerholm P, Fagerholm P, 

et al. Excimer laser photorefractive keratectomy for 

myopia: clinical results in sighted eyes.Ophthalmol.

May 1993; 100(5):739-45.
25

46. Klyce SD, Smolek MK. Corneal topography of excimer laser photorefractive keratectomy. J Cataract 

Refract Surg. Feb 1993; 19(Suppl):S122-30.

47. Krueger RR, Binder PS, McDonnell PJ. The effects 

of excimer laser photoablation on the cornea. In: 

Salz JJ, McDonnell PJ, McDonald MB, eds.Corneal 

Laser Surgery. St. Louis, MO: Mosby Year Book Inc; 

1995:11-44.

48. Aktunç R, Aktunç T. Centration of excimer laser 

photorefractive keratectomy and changes in astigmatism. J Refract Surg. Jan-Feb 1996; 12(Suppl):

S268-71.

49. Yavitz E. RK vs. PRK: Efficacy and outcome.Optom 

Manage. Dec 1994; 29(12):13.

50. Maguen E, Machat JJ. Complications of photorefractive keratectomy, primarily with the VISX 

excimer laser. In: Salz JJ, McDonnell PJ, McDonald 

MB, eds. Corneal Laser Surgery. St. Louis, MO: 

Mosby Year Book Inc; 1995:143-58.

51. Diamond S. Excimer laser photorefractive keratectomy (PRK) for myopia present status: Aeromedical 

considerations. Aviat Space Environ Med. Jul 1995; 

66(7):690-3.

52. Seiler T, Reckmann W, Maloney RK. Effective 

spherical aberration of the cornea as a quantitative 

descriptor in corneal topography.J Cataract Refract 

Surg. Feb 1993; 19(Suppl):S155-65.

53. Gartry DS. Treating myopia with the excimer 

laser: the present position. BMJ. Apr 15, 1995; 

310(6985):979-85.

54. Seiler T, McDonnell PJ. Excimer laser photorefractive keratectomy. Surv Ophthalmol. Sep-Oct 1995; 

40(2):89-118.

55. Citron C. Unpredictable corneal cictrization. Arch 

Ophthalmol. Nov 1990; 108(11):1540-1.

56. Maguire LJ, Bechara S. Epithelial distortions at the 

ablation zone margin after excimer laser photorefractive keratectomy for myopia. Am J Ophthalmol.

Jun 1994; 117(6):809-10.

57. Pacella E, Abdolrahimzadeh S, Gabrieli CB.

Excimer laser photorefractive keratectomy for 

hyperopia. Ophthalmic Surg Lasers. Jan-Feb 2001; 

32(1):30-4.

58. Wee TL, Chan WK, Tseng P, Tan D, et al. Excimer 

laser photorefractive keratectomy for the correction 

of myopia. Singapore Med J. Apr 1999; 40(4):246-

50.

59. Lipshitz I, Fisher L, Lazar M, Loewenstein A. Bilateral comparison of photorefractive keratectomy 

for myopia using two excimer lasers. J Refract Surg.

May-Jun 1999; 15(3):334-7.

60. Siganos DS, Pallikaris IG, Margaritis VN. Photorefractive keratectomy with a transition zone for 

myopia from -7 to -14 diopters. J Refract Surg. Feb 

1996; 12(2):S261-3.

61. Balakrishnan V, Lim AS, Low CH, Lee CP, et al.

Excimer laser photorefractive keratectomy in Singapore—a new treatment modality for myopia.

Singapore Med J. Aug 1993; 34(4):309-12.

62. Hersh PS, Stulting RD, Steinert RF, Waring GO 

3rd, et al. Results of phase III excimer laser photorefractive keratectomy for myopia. The Summit PRK Study Group. Ophthalmol. Oct 1997; 

104(10):1535-53.

63. Johnson DG, Kezirian GM, George SP, Casebeer 

JC, et al. Removal of corneal epithelium with 

phototherapeutic technique during multizone, 

multipass photorefractive keratectomy. J Refract 

Surg. Jan-Feb 1998; 14(1):38-48.

64. Kwitko ML, Gow J, Bellavance F, Wu J. Excimer 

laser photorefractive keratectomy: one year followup.Ophthalmic Surg Lasers. May 1996; 27(5 Suppl):

S454-7.

65. Machat JJ, Tayfour F. Photorefractive keratectomy 

for myopia: preliminary results in 147 eyes. Refract 

Corneal Surg. Mar-Apr 1993; 9(2 Suppl):S16-9.

66. Nagy ZZ, Fekete O, Suveges I. Photorefractive 

keratectomy for myopia with the Meditec MEL 

70G-Scan flying spot laser. J Refract Surg. May-Jun 

2001; 17(3):319-26.

67. Nagy ZZ, Suveges I, Nemeth J, Fust A. Refractive 

results after photorefractive excimer laser treatment 

in mild myopic and in mild hyperopic eyes. Acta 

Chir Hung. 1995-96; 35(3-4):315-24.

68. Ozdamar A, Aras C, Sener B, Bahcecioglu H.

Two-year results of photorefractive keratectomy 

with scanning spot ablation for myopia of less than 

-6.0 diopters. Ophthalmic Surg Lasers. Nov 1998; 

29(11):904-8.

69. Pallikaris I, McDonald MB, Siganos D, Klonos G, 

et al. Tracker-assisted photorefractive keratectomy 

for myopia of -1 to -6 diopters. J Refract Surg. Feb 

1996; 12(2):240-7.
26

70. Pietila J, Makinen P, Pajari S, Uusitalo H. Photorefractive keratectomy for -1.25 to -25.00 diopters of 

myopia. J Refract Surg. Nov-Dec 1998; 14(6):615-

22.

71. Shah S, Chatterjee A, Smith RJ. Predictability of 

spherical photorefractive keratectomy for myopia.

Ophthalmol. Dec 1998; 105(12):2178-84; discussion 2184-5.

72. Shen EP, Yang CN, Hu FR. Corneal astigmatic 

change after photorefractive keratectomy and 

photoastigmatic refractive keratectomy. J Cataract 

Refract Surg. Mar 2002; 28(3):491-8.

73. Tuunanen TH, Tervo TT. Results of photorefractive 

keratectomy for low, moderate, and high myopia.

J Refract Surg. Jul-Aug 1998; 14(4):437-46.

74. Fernandez AP, Jaramillo J, Jaramillo M. Comparison 

of photorefractive keratectomy and laser in situ 

keratomileusis for myopia of -6 D or less using 

the Nidek EC-5000 laser. J Refract Surg. Nov-Dec 

2000; 16(6):711-5.

75. Hamberg-Nystrom H, Fagerholm P, Tengroth B, 

Sjoholm C. Thirty-six month follow-up of excimer 

laser photorefractive keratectomy for myopia.

Ophthalmic Surg Lasers. May 1996; 27(5 Suppl):

S418-20.

76. Kapadia MS, Wilson SE. One-year results of PRK 

in low and moderate myopia: Fewer than 0.5% of 

eyes lose two or more lines of vision. Cornea. Mar 

2000; 19(2):180-4.

77. Piebenga LW, Matta CS, Deitz MR, Tauber J.

Two-zone excimer photorefractive keratectomy 

for moderate myopia. Six- to 18-month follow-up.

Ophthalmol. Jul 1995; 102(7):1054-9.

78. Talamo JH, Siebert K, Wagoner MD, Yeh E, et al.

Multicenter study of photorefractive keratectomy 

for myopia of 6.00 to 8.00 diopters. VISX Moderate 

Myopia Study Group.J Refract Surg. Jul-Aug 1995; 

11(4):238-47.

79. Williams DK. Multizone photorefractive keratectomy for high and very high myopia: longterm results. J Cataract Refract Surg. Sep 1997; 

23(7):1034-41.

80. Hersh PS, Brint SF, Maloney RK, Durrie DS, et 

al. Photorefractive keratectomy versus laser in situ 

keratomileusis for moderate to high myopia. A 

randomized prospective study. Ophthalmol. Aug 

1998; 105(8):1512-22, discussion 1522-3.

81. Keskinbora HK. Long-term results of multizone 

photorefractive keratectomy for myopia of -6.0 to 

-10.0 diopters. J Cataract Refract Surg. Oct 2000; 

26(10):1484-91.

82. Kim JH, Hahn TW, Lee YC, Sah WJ. Clinical 

experience of two-step photorefractive keratectomy 

in 19 eyes with high myopia. Refract Corneal Surg.

Mar-Apr 1993; 9(2 Suppl):S44-7.

83. Pop M, Payette Y. Multipass versus single pass 

photorefractive keratectomy for high myopia using a scanning laser. J Refract Surg. Jul-Aug 1999; 

15(4):444-50.

84. Spadea L, Colucci S, Bianco G, Balestrazzi E.

Long-term results of excimer laser photorefractive 

keratectomy in high myopia: A preliminary report.

Ophthalmic Surg Lasers. Jun 1998; 29(6):490-6.

85. Taylor HR, Kelly P, Alpins N. Excimer laser correction of myopic astigmatism. J Cataract Refract 

Surg. Mar 1994; 20(Suppl):243-51.

86. Danjoux JP, Fraenkel G, Lawless MA, Rogers C.

Treatment of myopic astigmatism with the Summit 

Apex Plus excimer laser.J Cataract Refract Surg. Dec 

1997; 23(10):1472-9.

87. Stevens J, Giubilei M, Ficker L, Rosen P. Prospective 

study of photorefractive keratectomy for myopia using the VISX StarS2 excimer laser system. J Refract 

Surg. Sep-Oct 2002; 18(5):502-8.

88. Stojanovic A, Nitter TA. 200 Hz flying-spot 

technology of the LaserSight LSX excimer laser in 

the treatment of myopic astigmatism: six and 12 

month outcomes of laser in situ keratomileusis and 

photorefractive keratectomy.J Cataract Refract Surg.

Aug 2001; 27(8):1263-77.

89. Shah S, Chatterjee A, Smith RJ. Predictability and 

outcomes of photoastigmatic keratectomy using the 

Nidek EC-5000 excimer laser. J Cataract Refract 

Surg. Apr 2002; 28(4):682-8.

90. Nagy ZZ, Krueger RR, Hamberg-Nystrom H, Fust 

A, et al. Photorefractive keratectomy for hyperopia 

in 800 eyes with the Meditec MEL 60 laser.J Refract 

Surg. Sep-Oct 2001; 17(5):525-33.

91. Pietila J, Makinen P, Pajari S, Uusitalo H. Excimer 

laser photorefractive keratectomy for hyperopia. J 

Refract Surg. Sep-Oct 1997; 13(6):504-10.
27

92. Dausch D, Smecka Z, Klein R, Schroder E, et 

al. Excimer laser photorefractive keratectomy for 

hyperopia. J Cataract Refract Surg. Mar 1997; 

23(2):169-76.

93 Kremer I, Gabbay U, Blumenthal M. One-year 

follow-up results of photorefractive keratectomy 

for low, moderate, and high primary astigmatism.

Ophthalmol. May 1996; 103(5):741-8.

94. Fisher EM, Ginsberg NE, Scher KS, Hersh PS.

Photorefractive keratectomy for myopia with a 

15 Hz repetition rate. J Cataract Refract Surg. Mar 

2000; 26(3):363-8.

95. Tabbara KF, El-Sheikh HF, Sharara NA, Aabed 

B. Corneal haze among blue eyes and brown eyes 

after photorefractive keratectomy.Ophthalmol. Nov 

1999; 106(11):2210-5.

96. Kim JH, Kim MS, Hahn TW, Lee YC, et al.

Five years results of photorefractive keratectomy 

for myopia. J Cataract Refract Surg. Jun 1997; 

23(5):731-5.

97. Kim JH, Hahn TW, Lee YC, Joo CK, et al. Photorefractive keratectomy in 202 myopic eyes: One 

year results. Refract Corneal Surg. Mar-Apr 1993; 

9(2 Suppl):S11-6.

98. Kim JH, Sah WJ, Kim MS, Lee YC, et al. Three-year 

results of photorefractive keratectomy for myopia.

J Refract Surg. May-Jun 1995; 11(3 Suppl):S248-

52.

99. Kim JH, Hahn TW, Lee YC, Sah WJ. Excimer 

laser photorefractive keratectomy for myopia: twoyear follow-up. J Cataract Refract Surg. Mar 1994; 

20(Suppl):229-33.

100. Schallhorn SC, Blanton CL, Kaupp SE, Sutphin J, 

et al. Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel.

Ophthalmol. Jan 1996; 103(1):5-22.

101. Tole DM, McCarty DJ, Couper T, Taylor HR.

Comparison of laser in situ keratomileusis and 

photorefractive keratectomy for the correction of 

myopia of -6.00 diopters or less. Melbourne Excimer Laser Group. J Refract Surg. Jan-Feb 2001; 

17(1):46-54.

102. Lee JB, Kim JS, Choe C, Seong GJ, et al. Comparison of two procedures: photorefractive keratectomy versus laser in situ keratomileusis for low 

to moderate myopia. Jpn J Ophthalmol. Sep-Oct 

2001; 45(5):487-91.

103. Wang Z, Pang G, Zheng W, Wang W, et al. [An 

analysis on follow-up results of photorefractive 

keratectomy for treatment of myopia.] [Article in 

Chinese, English] Zhonghua Yan Ke Za Zhi. May 

1995; 31(3):172-80.

104. El-Maghraby A, Salah T, Waring GO 3rd, Klyce S, 

et al. Randomized bilateral comparison of excimer 

laser in situ keratomileusis and photorefractive 

keratectomy for 2.50 to 8.00 diopters of myopia.

Ophthalmol. Mar 1999; 106(3):447-57.

105. Nagy ZZ, Munkacsy G, Popper M. Photorefractive 

keratectomy using the meditec MEL 70 G-scan 

laser for hyperopia and hyperopic astigmatism. J 

Refract Surg. Sep-Oct 2002; 18(5):542-50.

106. Williams DK. Excimer laser photorefractive keratectomy for extreme myopia.J Cataract Refract Surg.

Sep 1996; 22(7):910-4.

107. Wang Z, Chen J, Yang B. Comparison of laser in 

situ keratomileusis and photorefractive keratectomy 

to correct myopia from -1.25 to -6.00 diopters. J 

Refract Surg. Sep-Oct 1997; 13(6):528-34.

108. Loewenstein A, Lipshitz I, Varssano D, Lazar M.

Complications of excimer laser photorefractive 

keratectomy for myopia. J Cataract Refract Surg.

Oct 1997; 23(8):1174-6.

109. Alio JL, Artola A, Claramonte PJ, Ayala MJ, et al.

Complications of photorefractive keratectomy for 

myopia: two year follow-up of 3000 cases.J Cataract 

Refract Surg. May 1998; 24(5):619-26.

110. Ozdamar A, Aras C, Karakas N, Sener B, et al.

Changes in tear flow and tear film stability after 

photorefractive keratectomy. Cornea. Jul 1999; 

18(4):437-9.

111. Siganos DS, Popescu CN, Siganos CS, Pistola G.

Tear secretion following spherical and astigmatic 

excimer laser photorefractive keratectomy. J Cataract Refract Surg. Nov 2000; 26(11):1585-9.

112. Hefetz L, Domnitz Y, Haviv D, Krakowsky D, 

et al. Influence of patient age on refraction and 

corneal haze after photorefractive keratectomy. Br 

J Ophthalmol. Aug 1997; 81(8):637-8.

113. Corbett MC, O’Brart DP, Warburton FG, Marshall 

J. Biologic and environmental risk factors for regression after photorefractive keratectomy.Ophthalmol.

Sep 1996; 103(9):1381-91.
28

114. Sharif K. Regression of myopia induced by pregnancy after photorefractive keratectomy. J Refract 

Surg. Aug 1997; 13(5 Suppl):S445-6.

115. Stojanovic A, Nitter TA. Correlation between ultraviolet radiation level and the incidence of late-onset 

corneal haze after photorefractive keratectomy. J 

Cataract Refract Surg. Mar 2001; 27(3):404-10.

116. Lipshitz I, Loewenstein A, Varssano D, Lazar M.

Late onset corneal haze after photorefractive keratectomy for moderate and high myopia. Ophthalmol.

Mar 1997; 104(3):369-73; discussion 373-4.

117. Ben-Sira A, Loewenstein A, Lipshitz I, Levanon D, 

et al. Patient satisfaction after 5.0-mm photorefractive keratectomy for myopia.J Refract Surg. Mar-Apr 

1997; 13(2):129-34.

118. Brunette I, Gresset J, Boivin JF, Pop M, et al. Functional outcome and satisfaction after photorefractive keratectomy. Part 2: Survey of 690 patients.

Ophthalmol. Sep 2000; 107(9):1790-6.

119. Hamberg-Nystrom H, Tengroth B, Fagerholm 

P, Epstein D, et al. Patient satisfaction following 

photorefractive keratectomy for myopia. J Refract 

Surg. May-Jun 1995; 11(3 Suppl):S335-6.

120. Shah SS, Perera S, Chatterjee A. Satisfaction after 

photorefractive keratectomy. J Refract Surg. Apr 

1998; 14(2 Suppl):S226-7.

121. Goldberg MA, Dorr DA, Pepose JS. Lack of diurnal 

variation in vision, refraction, or keratometry after 

excimer laser photorefractive keratectomy. Am J 

Ophthalmol. Mar 1997; 123(3):407-8.

122. Vrabec MP, McDonald MB, Chase DS, Aitken PA, 

et al. Traumatic corneal abrasions after excimer laser 

keratectomy [letter]. Am J Ophthalmol. Jul 1993; 

116(1):101-2.

123. Martínez CE, Applegate RA, Klyce SD, McDonald 

MB, et al. Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy.

Arch Ophthalmol. Aug 1998; 116(8):1053-62.

124. Cotliar AM, Schubert HD, Mandel ER, Trokel SL.

Excimer laser radial keratotomy. Ophthalmol. Feb 

1985; 92(2):206-8.

125. Dusch D, Klein R, Schroder E. Excimer laser 

photorefractive keratectomy for hyperopia. Refract 

Corneal Surg. Jan-Feb 1993; 9(1):20-8.

126. Tavola A, Brancato R, Galli L, Carones F, et al.

Photorefractive keratectomy for myopia: single vs.

double-zone treatment in 166 eyes. Refract Corneal 

Surg. Mar-Apr 1993; 9(2 Suppl):S48-S52.

127. Tsubota K, Toda I, Itoh S. Reduction of subepithelial 

haze after photorefractive keratectomy by cooling 

the cornea [letter]. Am J Ophthalmol. Jun 1993; 

115(6):820-1.

128. Polunin GS, Kourenkov VV, Makarov IA, Polunina 

EG. The corneal barrier function in myopic eyes 

after laser in situ keratomileusis and after photorefractive keratectomy in eyes with haze formation.

J Refract Surg. Mar-Apr 1999; 15(2 Suppl):S221-

S24.

129. Shimizu K, Amano S, Tanaka S. Photorefractive 

keratectomy for myopia: one-year follow-up in 97 

eyes. J Refract Corneal Surg. Mar-Apr 1994; 10(2 

Suppl):S178-87.

130. O’Brart DPS, Corbett MC, Verma S, Heacock G, 

et al. Effects of ablation diameter, depth, and edge 

contour on the outcome of photorefractive keratectomy. J Refract Surg. Jan-Feb 1996; 12(1):50-60.

131. Vajpayee RB, McCarty CA, Aldred GF, Taylor 

HR. Undercorrection after excimer laser refractive 

surgery. Am J Ophthalmol. Dec 1996; 122(6):801-

807.

132. Durrie DS, Lesher MP, Hunkeler JD. Treatment 

of overcorrection after myopic photorefractive 

keratectomy.J Refract Corneal Surg. Mar-Apr 1994; 

10:S295.

133. Shah SS, Kapadia MS, Meisler DM, Wilson SE.

Photorefractive keratectomy using the summit SVS 

Apex laser with or without astigmatic keratotomy.

Cornea. Sep 1998; 17(5):508-16.

134. Zadnick K, Mutti DO. PRK vs. contact lenses; the 

risk is relative. Contact Lens Spectrum. Jan 1996; 

11(1):12.

135. Hovanesian JA, Shah SS, Maloney RK. Symptoms 

of dry eye and recurrent erosion syndrome after 

refractive surgery.J Cataract Refract Surg. Apr 2001; 

27(4):577-84.

136. Lee JB, Ryu CH, Kim J, Kim EK, et al. Comparison of tear secretion and tear film instability 

after photorefractive keratectomy and laser in situ 

keratomileusis. J Cataract Refract Surg. Sep 2000; 

26(9):1326-31.
29

137. Timo T, Mustonen R, Tarkkanen A. Management 

of dry eye may reduce haze after excimer laser 

photorefractive keratectomy. [letter] Refract Corneal 

Surg. Jul-Aug 1993; 9:306.

138. Duffey RJ, Leaming D. U.S. trends in refractive 

surgery: 2001 International Society of Refractive 

Surgery survey. J Refract Surg. Mar-Apr 2002; 

18(2):185-188.

139. Gilbert ML. LASIK Beneath the surface. Eyecare 

Technol. Jan 1996; 6(1):47-9.

140. Editor. LASIK wins FDA panel approval nod. AOA 

News. Jul 28, 1997; 36(2):1,6.

141. Augustine JM. Post-operative advantages of LASIK 

outweigh intraoperative risks. Primary Care Optom 

News. Mar 1996; 1(2):32.

142. Kremer FB, Gdovin GR. Update on LASIK: clinical results from 202 eyes. Rev Optom. Dec 1995; 

132(12):39-43.

143. Helmy SA, Salah A, Badawy TT, Sidky AN. Photorefractive keratectomy and laser in situ keratomileusis for myopia between 6.00 and 10.00 diopters.

J Refract Surg. Mar-Apr 1996;12(2):417-21.

144. Karpecki PM, Smith BJ, Smith JM. Excimer laser 

technology explores new horizons. Rev Optom. Oct 

1996; 133(10):63-4, 66.

145. Gimbel HV, Basti S, Kaye GB, Ferensowicz M.

Experience during the learning curve of laser in situ 

keratomileusis. J Cataract Refract Surg. Jun 1996; 

22(5):542-50.

146. Farah SG, Azar DT, Gurdal C, Wong J. Laser in 

situ keratomileusis: Literature review of a developing technique. J Cataract Refract Surg. Jul 1998; 

24(7):989-1006.

147. Güell JL, Muller A. Laser in situ keratomileusis 

(LASIK) for myopia from -7 to -18 diopters. J 

Refract Surg. Jan-Feb 1996; 12(2):222-8.

148. Aquavella JV. Shelving the microkeratome in favor of the laser. Contact Lens Spectrum. Jan 1996; 

11(1):48.

149. Joo CK, Kim TG. Corneal perforation during laser 

in situ keratomileusis. J Cataract Refract Surg. Aug 

1999; 25(8):1165-7.

150. Gimbel HV, Iskander NG, Peters NT, Penno EA.

Prevention and management of microkeratomerelated laser in situ keratomileusis complications. J 

Refract Surg. Mar-Apr 2000; 16(2 Suppl):S226-9.

151. Leung AT, Rao SK, Cheng AC, Yu EW, et al.

Pathogenesis and management of laser in situ 

keratomileusis flap buttonhole. J Cataract Refract 

Surg. Mar 2000; 26(3):358-62.

152. Levartovsky S, Rosenwasser G, Goodman D. Bacterial keratitis following laser in situ keratomileusis.

Ophthalmol. Feb 2001; 108(2):321-5.

153. Parolini B, Marcon G, Panozzo GA. Central 

necrotic lamellar inflammation after laser in situ 

keratomileusis. J Refract Surg. Mar-Apr 2001; 

17(2):110-2.

154. Kim EK, Lee DH, Lee K, Lim SJ, et al. Nocardia 

keratitis after traumatic detachment of a laser in situ 

keratomileusis flap. J Refract Surg. Jul-Aug 2000; 

16(4):467-9.

155. Cameron BD, Saffra NA, Strominger MB. Laser 

in situ keratomileusis-induced optic neuropathy.

Ophthalmol. Apr 2001; 108(4):660-5.

156. Stephenson M. RRD after LASIK must be managed 

promptly. Ocular Surg News Europe/Asia-Pacific 

Edition. April 4, 2001.

157. Farah ME, Hofling-Lima AL, Nascimento E. Early 

rhegmatogenous retinal detachment following laser 

in situ keratomileusis for high myopia. J Refract 

Surg. Nov-Dec 2000; 16(6):739-43.

158. Aras C, Ozdamar A, Bahcecioglu H, Karacorlu 

M, et al. Decreased tear secretion after laser in situ 

keratomileusis for high myopia. J Refract Surg.

May-Jun 2000; 16(3):362-4.

159. Balazsi G, Mullie M, Lasswell L, Lee PA, et al. Laser 

in situ keratomileusis with a scanning excimer laser 

for the correction of low to moderate myopia with 

and without astigmatism. J Cataract Refract Surg.

Dec 2001; 27(12):1942-51.

160. Rao S, Cheng ACK, Fan DSP, Leung ATS, et al.

Effect of preoperative keratometry on refractive 

outcomes after laser in situ keratomileusis.J Cataract 

Refract Surg. Feb 2001; 27(2):297-302.

161. Haw WW, Manche EE. Large optical ablation zone 

using the VISX S2 smooth scan excimer laser. J 

Cataract Refract Surg. Dec 2000; 26(12):1742-7.

162. Knorz MC, Wiesinger B, Liermann A, Seiberth V, 

et al. Laser in situ keratomileusis for moderate and 

high myopia and myopic astigmatism.Ophthalmol.

May 1998; 105(5):932-40.
30

163. McDonald MB, Carr JD, Frantz JM, Kozarsky 

AM, et al. Laser in situ keratomileusis for myopia 

up to -11 diopters with up to -5 diopters of astigmatism with the summit autonomous LADARVision excimer laser system. Ophthalmol. Feb 2001; 

108(2):309-16.

164. Mulhern MG, Condon PI, O’Keefe M. Myopic and 

hyperopic laser in situ keratomileusis retreatments: 

indications, techniques, limitations, and results.

Cataract Refract Surg. Aug 2001; 27(8):1278-87.

165. Pesando PM, Ghiringhello MP, Tagliavacche P.

Excimer laser in situ keratomileusis for myopia. J 

Refract Surg. Sep-Oct 1997; 13(6):521-7.

166. Nordan LT, Slade SG, Baker RN, Suarez C, et al.

Femtosecond laser flap creation for laser in situ 

keratomileusis: six-month follow-up of initial U.S.

clinical series.J Refract Surg. Jan-Feb 2003; 19(1):8-

14.

167. McGhee CN, Craig JP, Sachdev N, Weed KH, 

et al. Functional, psychological, and satisfaction outcomes of laser in situ keratomileusis for 

high myopia. J Cataract Refract Surg. Apr 2000; 

26(4):497-509.

168. Brint SF, Ostrick DM, Fisher C, Slade SG, et al.

Six-month results of the multicenter phase I study 

of excimer laser myopic keratomileusis. J Cataract 

Refract Surg. Nov 1994; 20:610-5.

169. Dada T, Sudan R, Sinha R, Ray M, et al. Results 

of laser in situ keratomileusis for myopia of -10 to 

-19 diopters with a Technolas 217 laser. J Refract 

Surg. Jan-Feb 2003; 19(1):44-7.

170. El Danasoury MA, El Maghraby A, Gamali TO.

Comparison of iris-fixed Artisan lens implantation 

with excimer laser in situ keratomileusis in correcting myopia between -9.00 and -19.50 diopters: 

a randomized study. Ophthalmol. May 2002; 

109(5):955-64.

171. Kawesch GM, Kezirian GM. Laser in situ keratomileusis for high myopia with the VISX star 

laser. Ophthalmol. Apr 2000; 107(4):653-61.

172. Lyle WA, Jin GJ. Laser in situ keratomileusis with 

the VISX Star laser for myopia over -10.0 diopters.

J Cataract Refract Surg. Nov 2001; 27(11):1812-

22.

173. Reviglio VE, Bossana EL, Luna JD, Muino JC, 

et al. Laser in situ keratomileusis for myopia and 

hyperopia using the Lasersight 200 laser in 300 

consecutive eyes. J Refract Surg. Nov-Dec 2000; 

16(6):716-23.

174. Knorz MC, Neuhann T. Treatment of myopia 

and myopic astigmatism by customized laser in 

situ keratomileusis based on corneal topography.

Ophthalmol. Nov 2000; 107(11):2072-6.

175. Montes M, Chayet A, Gomez L, Magallanes R, et 

al. Laser in situ keratomileusis for myopia of -1.50 

to -6.00 diopters. J Refract Surg. Mar-Apr 1999; 

15(2):106-10.

176. Zaldivar R, Davidorf JM, Shultz MC, Oscherow 

S. Laser in situ keratomileusis for low myopia and 

astigmatism with a scanning spot excimer laser. J 

Refract Surg. Nov-Dec 1997; 13(7):614-9.

177. Fraenkel GE, Webber SK, Sutton GL, Lawless MA, 

et al. Toric laser in situ keratomileusis for myopic 

astigmatism using an ablatable Mask.J Refract Surg.

Mar-Apr 1999; 15(2):111-7.

178. Dulaney DD, Barnet RW, Perkins SA, Kezirian 

GM. Laser in situ keratomileusis for myopia and 

astigmatism: 6 month results. J Cataract Refract 

Surg. Jun 1998; 24(6):758-64.

179. Shaikh NM, Manche EE. Laser in situ keratomileusis for myopia and compound myopic astigmatism 

using the Technolas 217 scanning-spot laser. J 

Cataract Refract Surg. Mar 2002; 28(3):485-90.

180. Zaldivar R, Davidorf JM, Oscherow S. Laser in situ 

keratomileusis for myopia from -5.50 to -11.50 

diopters with astigmatism. J Refract Surg. Jan-Feb 

1998; 14(1):19-25.

181. Chitkara DK, Rosen E, Gore C, Howes F, et al.

Tracker-assisted laser in situ keratomileusis for myopia using the autonomous scanning and tracking 

laser: 12-month results. Ophthalmol. May 2002; 

109(5):965-72.

182. Argento CJ, Cosentino MJ. Comparison of optical 

zones in hyperopic laser in situ keratomileusis: 5.9 

mm versus smaller optical zones. J Cataract Refract 

Surg. Aug 2000; 26(8):1137-46.

183. Argento CJ, Cosentino MJ. Laser in situ keratomileusis for hyperopia. J Cataract Refract Surg. Aug 

1998; 24(8):1050-8.
31

184. el-Agha MS, Johnston EW, Bowman RW, Cavanagh 

HD, et al. Excimer laser treatment of spherical 

hyperopia: PRK or LASIK? Trans Am Ophthalmol 

Soc. 2000; 98:59-66; discussion 66-9.

185. Lindstrom RL, Linebarger EJ, Hardten DR, 

Houtman DM, et al. Early results of hyperopic 

and astigmatic laser in situ keratomileusis in eyes 

with secondary hyperopia. Ophthalmol. Oct 2000; 

107(10):1858-63.

186. Zadok D, Maskaleris G, Montes M, Shah S, et 

al. Hyperopic laser in situ keratomileusis with the 

Nidek EC-5000 excimer laser. Ophthalmol. Jun 

2000; 107(6):1132-7.

187. Esquenazi S, Mendoza A. Two-year follow-up of 

laser in situ keratomileusis for hyperopia. J Refract 

Surg. Nov-Dec 1999; 15(6):648-52.

188. Choi RY, Wilson SE. Hyperopic laser in situ keratomileusis: primary and secondary treatments are 

safe and effective. Cornea. May 2001; 20(4):388-

93.

189. Ditzen K, Fiedler J, Pieger S. Laser in situ keratomileusis for hyperopia and hyperopic astigmatism 

using the Meditec MEL 70 spot scanner. J Refract 

Surg. Jul-Aug 2002; 18(4):430-4.

190. Lian J, Ye W, Zhou D, Wang K. Laser in situ 

keratomileusis for correction of hyperopia and 

hyperopic astigmatism with the Technolas 117C.

J Refract Surg. Jul-Aug 2002; 18(4):435-8.

191. Salz JJ, Stevens CA, LADARVision LASIK Hyperopia Study Group. LASIK correction of spherical hyperopia, hyperopic astigmatism, and mixed 

astigmatism with the LADARVision excimer laser 

system. Ophthalmol. Sep 2002; 109(9):1647-56; 

discussion 1657-8.

192. Tabbara KF, El-Sheikh HF, Islam SM. Laser in situ 

keratomileusis for the correction of hyperopia from 

+0.50 to +11.50 diopters with the Keracor 117C 

laser. J Refract Surg. Mar-Apr 2001; 17(2):123-8.

193. Goker S, Er H, Kahvecioglu C. Laser in situ 

keratomileusis to correct hyperopia from +4.25 

to +8.00 diopters. J Refract Surg. Jan-Feb 1998; 

14(1):26-30.

194. Chayet AS, Magallanes R, Montes M, Chavez S, et 

al. Laser in situ keratomileusis for simple myopic, 

mixed, and simple hyperopic astigmatism.J Refract 

Surg. Apr 1998; 14(2 Suppl):S175-6.

195. Rashad KM. Laser in situ keratomileusis for the correction of hyperopia from +1.25 to +5.00 diopters 

with the Technolas Keracor 117C laser. J Refract 

Surg. Mar-Apr 2001; 17(2):113-22.

196. Pirzada WA, Kalaawry H. Laser in situ keratomileusis for myopia of -1 to -3.50 diopters. J Refract 

Surg. Aug 1997; 13(5 Suppl):S425-6.

197. Chayet AS, Montes M, Gomez L, Rodriguez X, et 

al. Bitoric laser in situ keratomileusis for the correction of simple myopic and mixed astigmatism.

Ophthalmol. Feb 2001; 108(2):303-8.

198. Argento CJ, Cosentino MJ, Biondini A. Treatment 

of hyperopic astigmatism. J Cataract Refract Surg.

Dec 1997; 23(10):1480-90.

199. el Danasoury MA, el Maghraby A, Klyce SD, 

Mehrez K. Comparison of photorefractive keratectomy with excimer laser in situ keratomileusis 

in correcting low myopia (from -2.00 to -5.50 

diopters). A randomized study. Ophthalmol. Feb 

1999; 106(2):411-20; discussion 420-1.

200. Pop M, Payette Y. Photorefractive keratectomy versus laser in situ keratomileusis: a control-matched 

study. Ophthalmol. Feb 2000; 107(2):251-7.

201. Pineda-Fernandez A, Rueda L, Huang D, Nur J, 

et al. Laser in situ keratomileusis for hyperopia 

and hyperopic astigmatism with the Nidek EC5000 Excimer laser. J Refract Surg. Nov-Dec 2001; 

17(6):670-5.

202. Reviglio VE, Luna JD, Rodriguez ML, Garcia FE, 

et al. Laser in situ keratomileusis using the LaserSight 200 laser: results of 950 consecutive cases. J 

Cataract Refract Surg. Aug 1999; 25(8):1062-8.

203. Knorz MC, Liermann A, Seiberth V, Steiner H, et 

al. Laser in situ keratomileusis to correct myopia 

of -6.00 to -29.00 diopters. J Refract Surg. Jul-Aug 

1996; 12(5):575-84.

204. Tsai RJ. Laser in situ keratomileusis for myopia of 

-2 to -25 diopters. J Refract Surg. Aug 1997; 13(5 

Suppl):S427-S29.

205. Han HS, Song JS, Kim HM. Long-term results of 

laser in situ keratomileusis for high myopia. Korean 

J Ophthalmol. Jun 2000; 14(1):1-6.

206. Kim HM, Jung HR. Laser assisted in situ keratomileusis for high myopia.Ophthalmic Surg Lasers. May 

1996; 27(5 Suppl):S508-S11.
32

207. Pallikaris IG, Siganos DS. Laser in situ keratomileusis to treat myopia: early experience. J Cataract 

Refract Surg. Jan-Feb 1997; 23(1):39-49.

208. Condon PI, Mulhern M, Fulcher T, Foley-Nolan 

A, et al. Laser intrastromal keratomileusis for high 

myopia and myopic astigmatism. Br J Ophthalmol.

Mar 1997; 81(3):199-206.

209. Siganos DS, Popescu CN, Siganos CS, Margaritis 

VN. Seven years experience with LASIK for myopia.

Oftalmologia. 1999; 47(2):50-2.

210. Barraquer C, Gutierrez AM. Results of laser in situ 

keratomileusis in hyperopic compound astigmatism.J Cataract Refract Surg. Sep 1999; 25(9):1198-

204.

211. Merchea M, Pieger S, Bains HS. Comparison of laser 

in situ keratomileusis outcomes with the Nidek EC5000 and Meditec Mel 70 excimer lasers. J Refract 

Surg. May-Jun 2002; 18(3 Suppl):S343-S46.

212. Merchea M, Tokarewicz A. Comparison of laser in 

situ keratomileusis outcomes with the Nidek EC5000 and LSX LaserSight excimer lasers. J Refract 

Surg. Mar-Apr 2001; 17(2 Suppl):S246-9.

213. Arbelaez MC, Knorz MC. Laser in situ keratomileusis for hyperopia and hyperopic astigmatism. J 

Refract Surg. Jul-Aug 1999; 15(4):406-14.

214. Ditzen K, Huschka H, Pieger S. Laser in situ keratomileusis for hyperopia. J Cataract Refract Surg.

Jan 1998; 24(1):42-7.

215. Hill JC. An informal satisfaction survey of 200 

patients after laser in situ keratomileusis. J Refract 

Surg. Jul-Aug 2002; 18(4):454-9.

216. Miller AE, McCulley JP, Bowman RW, Cavanagh 

HD, et al. Patient satisfaction after LASIK for 

myopia. CLAO J. Apr 2001; 27(2):84-8.

217. Laser Vision Correction by the Numbers. At URL: 

www.tlcv.com/newsroom/media_kit/ TLC%20L

VC%20By%20the%20Numbers.pdf (Accessed 

10/01).

218. TLC Laser Centers. Why choose TLC? At URL: 

www.tlcvision.com/why_choose_tlc/ (Accessed 

8/04).

219. Laser Eye Consults of Boston. Laser vision correction (brochure). At URL: www.corneaconsultantsboston.com/specialties/lasikbrochure.pdf (Accessed 

8/04).

220. Jacobs JM, Sanderson MC, Spivack LD, Wright 

JR, et al. Hyperopic laser in situ keratomileusis 

to treat overcorrected myopic LASIK. J Cataract 

Refract Surg. Mar 2001; 27(3):389-95.

221. Rosa DA. Laser in situ keratomileusis: three unexpected complications. J Refract Surg. Mar-Apr 

2001; 17(2 Suppl):S177-9.

222. Ismail MM, Alió JL, Pérez-Santonja JJ. Noncontact 

thermokeratoplasty to correct hyperopia induced 

by laser in situ Keratomileusis. J Cataract Refract 

Surg. Sep 1998; 24(9):1191-4.

223. el Danasoury MA, Waring GO, El Maghraby A, 

Mehrez K. Excimer laser in situ keratomileusis to 

correct compound myopic astigmatism. J Refract 

Surg. Sep-Oct 1997; 13(6):511-20.

224. el Danasoury MA. Prospective bilateral study of 

night glare after laser in situ keratomileusis with 

single zone and transition zone ablation. J Refract 

Surg. Sep-Oct 1998; 14(5):512-6.

225. Knorz MC, Hugger P, Jendritzka B, Liermann A.

Twilight visual acuity after correction of myopia 

with LASIK. [German] Ophthalmologe. Nov 1999; 

96(11):711-6.

226. Lyle WA, Jin GJ. Results of flap repositioning after 

laser in situ keratomileusis. J Cataract Refract Surg.

Oct 2000; 26(10):1451-7.

227. Wilson SE. Laser in situ keratomileusis induced 

(presumed) neurotrophic epitheliopathy. Ophthalmol. Jun 2001; 108(6):1082-7.

228. Leung AT, Rao SK, Lam DS. Traumatic partial 

unfolding of laser in situ keratomileusis flap with 

severe epithelial ingrowth. J Cataract Refract Surg.

Jan 2000; 26(1):135-9.

229. Geggel HS, Coday MP. Late-onset traumatic laser 

in situ keratomileusis (LASIK) flap dehiscence. Am 

J Ophthalmol. Apr 2001; 131(4):505-6.

230. Melki SA, Talamo JH, Demetriades AM, Jabbur 

NS, et al. Late traumatic dislocation of laser in 

situ keratomileusis corneal flaps. Ophthalmol. Dec 

2000; 107(12):2136-9.

231. Weisenthal RW. Diffuse lamellar keratitis induced 

by trauma 6 months after laser in situ keratomileusis.

J Refract Surg. Nov-Dec 2000; 16(6):749-51.

232. Lemley HL, Chodosh J, Wolf TC, Bogie CP, et al.

Partial dislocation of laser in situ keratomileusis 

flap by air bag injury.J Refract Surg. May-Jun 2000; 

16(3):373-4
33

233. Lombardo AJ, Katz HR. Late partial dislocation of 

a laser in situ keratomileusis flap. J Cataract Refract 

Surg. Jul 2001; 27(7):1108-10.

234. Mifflin M. Laser in situ keratomileusis flap dehiscence 3 years post-operatively J Cataract Refract 

Surg. May 2002; 28(5):733-35.

235. Patel CK, Hanson R, McDonald B, Cox N. Case 

reports and small case series: late dislocation of a 

LASIK flap caused by a fingernail.Arch Ophthalmol.

Mar 2001; 119(3):447-9.

236. Schwartz GS, Park DH, Schloff S, Lane SS. Traumatic flap displacement and subsequent diffuse 

lamellar keratitis after laser in situ keratomileusis.

J Cataract Refract Surg. May 2001; 27(5):781-3.

237. Lee BJ, Seong GJ, Lee JH, Seo KY, et al. Comparison 

of laser epithelial keratomileusis and photorefractive 

keratectomy for low to moderate myopia.J Cataract 

Refract Surg. Apr 2001; 27(4):565-70.

238. Azar DT, Ang RT, Lee JB, Kato T, et al. Laser subepithelial keratomileusis: electron microscopy and 

visual outcomes of flap photorefractive keratectomy.

Curr Opin Ophthalmol. Aug 2001; 12(4):323-8.

239. Lohmann CP, Winkler Von Mohrenfels C, Gabler 

B, Hermann W, et al. Excimer laser subepithelial 

ablation (ELSA) or laser epithelial keratomileusis 

(LASEK) - a new kerato-refractive procedure for 

myopia. Surgical technique and first clinical results 

on 24 eyes and 3 months follow-up. [Article in 

German] Klin Monatsbl Augenheilkd. Jan-Feb 2002; 

219(1-2):26-32.

240. Kornilovsky IM. Clinical results after subepithelial 

photorefractive keratectomy (LASEK). J Refract 

Surg. Mar-Apr 2001; 17(2 Suppl):S222-3.

241. Claringbold TV. Laser-assisted subepithelial keratectomy for the correction of myopia. J Cataract 

Refract Surg. Jan 2002; 28(1):18-21.

242. Rouweyha RM, Chuang AZ, Mitra S, Phillips CB, 

et al. Laser epithelial keratomileusis for myopia with 

the autonomous laser.J Refract Surg. May-Jun 2002; 

18(3):217-24.

243. Vinciguerra P, Camesasca FI. Butterfly laser epithelial keratomileusis for myopia. J Refract Surg.

May-Jun 2002; 18(3 Suppl):S371-3.

244. Lee JB, Choe CM, Kim HS, Seo KY, et al. Comparison of TGF-beta1 in tears following laser subepithelial keratomileusis and photorefractive keratectomy.

J Refract Surg. Mar-Apr 2002; 18(2):130-4.

245. Nakamura K, Kurosaka D, Bissen-Miyajima H, 

Tsubota K. Intact corneal epithelium is essential for 

the prevention of stromal haze after laser assisted 

in situ keratomileusis. Br J Ophthalmol. Feb 2001; 

85(2):209-13.

246. Rokita-Wala I, Gierek-Ciaciura S, MrukwaKominek E, Obidzinski M. Vital changes in corneal 

structure after LASEK during the early post-operative period. [Article in Polish] Klin Oczna. 2002; 

104(1):13-8.

247. Anderson NJ, Beran RF, Schneider TL. EpiLASEK for the correction of myopia and myopic 

astigmatism. J Cataract Refract Surg. Aug 2002; 

28(8):1343- 7.

248. Shahinian L Jr. Laser-assisted subepithelial keratectomy for low to high myopia and astigmatism. J 

Cataract Refract Surg. Aug 2002; 28(8):1334-42.

249. Shah S, Sebai Sarhan AR, Doyle SJ, Pillai CT, et al.

The epithelial flap for photorefractive keratectomy.

Br J Ophthalmol. Apr 2001; 85(4):393-6.

250. Durrie DS, Schumer DJ, Cavanaugh TB. Holmium:YAG laser thermokeratoplasty for hyperopia.

J Refract Corneal Surg. Mar-Apr 1994; 10(2 Suppl):

S277-80.

251. Dausch D, Landesz M, Koch DD, Berry MJ, et al.

Laser correction of hyperopia. In: Salaz JJ, Mcdonnell PJ, McDonald MB, eds. Corneal Laser Surgery.

St. Louis, MO: Mosby Year Book Inc; 1995:237-

60.

252. Haw WW, Manche EE. Conductive keratoplasty 

and laser thermal keratoplasty.Int Ophthalmol Clin.

Fall 2002; 42(4):99-106.

253. Medical Device Approvals, New Device Approval.

Hyperion LTK System – P990078. At URL: 

www.fda.gov/cdrh/mda/docs/p990079.html. (Accessed 7/02).

254. Moreira H, Campos M, Sawusch MR, McDonnell JM, et al. Holmium laser thermokeratoplasty.

Ophthalmol. May 1993; 100(5):752-61.

255. Nano HD, Muzzin S. Noncontact holmium:YAG 

laser thermal keratoplasty for hyperopia. J Cataract 

Refract Surg. Jun 1998; 24(6):751-7.
34

256. Ronge LJ. Noncontact Ho:YAG LTK show promise 

for low hyperopia. Ophthalmol World News. May 

1996; 2(5):1-2.

257. Facts you need to know about the ViewPoint-CK 

System and the Conductive Keratoplasty (CK) 

Procedure. Patient Information Booklet For Farsightedness (Hyperopia) Refractec, Inc. At URL: 

www.refractec.com. (Accessed 7/02).

258. Marshall BD, Stein JJ. How to choose what’s best for 

your patients. Optom Mgmt. May 2004. 39(5):38-

45.

259. McDonald MB, Davidorf J, Maloney RK, Manche 

EE, et al. Conductive keratoplasty for the correction 

of low to moderate hyperopia: 1-year results on the 

first 54 eyes. Ophthalmol. Apr 2002; 109(4):637-

49.

260. Asbell PA, Maloney RK, Davidorf J, Hersh P, et 

al. Conductive keratoplasty for the correction of 

hyperopia.Trans Am Ophthalmol Soc. 2001; 99:79-

84.

261. Burris TE. Intrastromal corneal ring technology: 

results and indications. Curr Opin Ophthalmol.

Aug 1998; 9(4):9-14.

262. Ruckhofer J, Stoiber J, Alzner E, Grabner G, et al.

One year results of European Multicenter Study of 

intrastromal corneal ring segments. Part 1: Refractive outcomes. J Cataract Refract Surg. Feb 2001; 

27(2):277-86.

263. Holmes-Higgin DK, Burris TE, Asbell PA, Durrie 

DS, et al. Topographic predicted corneal acuity with 

intrastromal corneal ring segments. J Refract Surg.

May-Jun 1999; 15(3):324-30.

264. Holmes-Higgin DK, Baker PC, Burris TE, Silvestrini TA. Characterization of the aspheric corneal 

surface with intrastromal corneal ring segments. J 

Refract Surg. Sep-Oct 1999; 15(5):520-8.

265. Schanzlin DJ. Studies of intrastromal corneal ring 

segments for the correction of low to moderate 

myopic refractive errors. Transactions Am Ophthalmol Soc. 1999; 97:815-90.

266. Ruckhofer J, Alzner E, Grabner G. Intrastromal 

corneal ring segments (ICRS, Kera Vision Ring).

One year outcome of the first 25 interventions.

[Article in German] Klin Monatsbl Augenheilkd.

Sep 1998; 213(3):147-53.

267. Twa MD, Hurst TJ, Walker JG, Waring GO, et al.

Diurnal stability of refraction after implantation 

with intracorneal ring segments. J Cataract Refract 

Surg. Apr 2000; 26(4):516-23.

268. Asbell PA, Ucakhan OO, Durrie DS, Lindstrom 

RL. Adjustability of refractive effect for corneal ring 

segments.J Refract Surg. Nov-Dec 1999; 15(6):627-

31.

269. Hoh H, Rehfeldt K, Reiss G. Correction of myopia 

with the intracorneal ring. [Article in German] 

Ophthalmologe. Nov 1999; 96(11):717-23.

270. Barach D, Mortemousque B, Bertel F, Diemer C, 

et al. Fluctuations in uncorrected visual acuity after 

refractive surgery using intra-stromal corneal rings.

[Article in French] J Fr Ophtalmol. Apr 1999; 

22(3):335-8.

271. Ruckhofer J, Stoiber J, Alzner E, Grabner G, et al.

One year results of European Multicenter Study of 

intrastromal corneal ring segments. Part 2: Complications, visual symptoms, and patient satisfaction.

J Cataract Refract Surg. Feb 2001; 27(2):287-96.

272. Editor. Intacs sales rise 86.7 percent. AOA News.

Jan 27, 2003; 41(14):6.

273. Thompson RW, Choi DM, Price FW Jr. Clear lens 

replacement surgery.Int Ophthalmol Clin. Fall 2002: 

42(2):131-152.

274. Seiler T. Clear lens extraction in the 19th century—

an early demonstration of premature dissemination.

J Refract Surg. Jan-Feb 1999; 15(1):70-3.

275. Werblin TP. Why should refractive surgeons be 

looking beyond the cornea? J Refract Surg. May-Jun 

1999; 15(3):357-76.

276. Colin J, Robinet A, Cochener B. Retinal detachment 

after clear lens extraction for high myopia; seven year 

follow-up. Ophthalmol. Dec 1999; 106:2281-5.

277. Lee KW, Lee JH. Long-term results of clear lens 

extraction for severe myopia.J Cataract Refract Surg.

Dec 1996; 22(10):1411-5.

278. Pucci V, Morselli S, Romanelli F, Pignatto S, et 

al. Clear lens phacoemulsification for correction 

of high myopia. J Cataract Refract Surg. Mar-Apr 

2001; 27(2):896-900.

279. Lyle WA, Jin GJC. Clear lens extraction to correct 

high myopia. J Cataract Refract Surg. Sep 1997; 

23(7):1051-6.
35

280. Kolahdouz-Isfahani AH, Rostamian K, Wallace D, 

Salz JJ. Clear lens extraction with intraocular lens 

implantation for hyperopia.J Refract Surg. May-Jun 

1999; 15(3):316-23.

281. Steinert RF, Aker BL, Trentacost DJ, Smith PJ, et al.

A prospective comparative study of the AMO Array 

zonal-progressive multifocal silicone intraocular 

lens and a monofocal intraocular lens. Ophthalmol.

Jul 1999; 106:1243-55.

282. Packer M, Fine IH, Hoffman RS. Refractive lens 

exchange with the Array Multifocal intraocular lens.

J Cataract Refract Surg. Mar 2002; 28(3):421-4.

283. Arens B, Freudenthaler N, Quentin CD. Binocular 

function after bilateral implantation of monofocal and refractive multifocal intraocular lenses. J 

Cataract Refract Surg. Mar 1999; 25:399-404.

284. Vaquero-Ruano M, Encinas JL, Millan I. AMO Array multifocal versus monofocal intraocular lenses: 

long term follow-up. J Cataract Refract Surg. Jan 

1998; 24:118-23.

285. Ravalico G, Parentin F, Pastori G, Baccara F. Spatial resolution threshold in pseudophakic patients 

with monofocal and multifocal intraocular lenses.

J Cataract Refract Surg. Feb 1998; 24:244-8.

286. Haring G, Gronemeyer A, Hedderich J, de Decker 

W. Stereoacuity and aniseikonia after unilateral 

and bilateral implantation of the Array refractive 

multifocal intraocular lens. J Cataract Refract Surg.

Aug 1999; 25:1151-6.

287. Featherstone KA, Bloomfield JR, Lang AJ, MillerMeeks MJ, et al. Driving simulation study: bilateral 

Array multifocal versus bilateral AMO monofocal 

intraocular lenses.J Cataract Refract Surg. Sep 1999; 

25:1254-62.

288. CrystaLensTM Posterior Chamber Accommodating 

Intraocular Lens For the Correction of Aphakia in 

Cataract Patients, PMA P030002, Presentation to 

the Ophthalmic Devices Advisory Panel May 23, 

2003.

289. Cummings JS, Slade SG, Chayet A, AT-45 Study 

Group. Clinical evaluation of the model AT-45 

Silicone accommodating intraocular lens; results 

of feasibility and the initial phase of a Food and 

Drug Administration clinical trial. Ophthalmol.

Nov 2001; 108(11):2005-10.

290. Dick HB, Gross S, Tehrani M, Eisemann D, et al.

Refractive lens exchange with an array multifocal 

intraocular lens. J Refract Surg. Sep-Oct 2002; 

18(5):509-18.

291. Gris O. Manero F, Muller A. Clear lens extraction 

to correct high myopia. J Cataract Refract Surg.

Jul-Aug 1996; 22(6):686-9.

292. Siganos DS, Pallikaris IG. Clear lensectomy and 

intraocular lens implantation for hyperopia from 

+7 to +14 diopters. J Refract Surg. Mar-Apr 1998; 

14(2):105-13.

293. Jimenez-Alfaro I, Migueles S, Bueno JL, Puy P.

Clear lens extraction and implantation of negative-power posterior chamber intraocular lenses 

to correct extreme myopia. J Cataract Refract Surg.

Oct 1998; 24(10):1310-6.

294. Siganos DS, Siganos CS, Pallikaris IG. Clear lens 

extraction and intraocular lens implantation in 

normally sighted hyperopic eyes. J Refract Corneal 

Surg. Mar-Apr 1994; 10(2):117-21.

295. Shingleton BJ, Wadhwani RA, O’Donoghue MW, 

Baylus S, et al. Evaluation of intraocular pressure 

in the immediate period after phacoemulsification.

J Cataract Refract Surg. Apr 2001; 27(4):524-7.

296. Colin J, Robinet A, Cochener B. Retinal detachment after clear lens extraction for high myopia: 

Seven-year follow-up. Ophthalmol. Dec 1999; 

106(12):2281-4; discussion 2285.

297. Ramos M, Kruger EF, Lashkari K. Biostatistical analysis of pseudophakic and aphakic retinal 

detachments. Semin Ophthalmol. Sep-Dec 2002; 

17(3-4):206-13.

298. Norregaard JC, Thoning H, Andersen TF, Bernth-Petersen P, et al. Risk of retinal detachment 

following cataract extraction: Results from the 

International Cataract Surgery Outcomes Study.

Br J Ophthalmol. Aug 1996; 80(8):689-93.

299. Javitt JC, Vitale S, Canner JK, Krakauer H, et al.

National outcomes of cataract extraction. I. Retinal 

detachment after inpatient surgery.Ophthalmol. Jun 

1991; 98(6):895-902.

300. Javitt JC, Street DA, Tielsch JM, Wang Q, et al.

National outcomes of cataract extraction. Retinal 

detachment and endophthalmitis after outpatient 

cataract surgery. Cataract Patient Outcomes Research Team. Ophthalmol. Jan 1994; 101(1):100-5; 

discussion 106.
36

301. Kaya V, Kevser MA, Yilmaz OF. Phakic posterior 

chamber plate intraocular lenses for high myopia.

J Refract Surg. Sep-Oct 1999; 15(5):580-5.

302. Barraquer J. Precrystalline posterior chamber intraocular lens for surgical correction of severe myopia.

Am J Ophthalmol. Aug 1999; 128(2):232-4.

303. Hruba H, Vlkova E, Horackova M, Svacinova J.

Comparison of clinical results between LASIK 

method and ICL implantation in high myopia 

[Article in Czech] Cesk Slov Oftalmol. May 2004; 

60(3):180-91.

304. Menezo JL, Peris-Martinez C, Cisneros AL, Martinez-Costa R. Phakic intraocular lenses to correct 

high myopia: Adatomed, Staar, and Artisan. J 

Cataract Refract Surg. Jan ; 30(1):33-44.

305. Gierek-Ciaciura S, Ochalik K, Gierek-Lapinska 

A, Myga B. Correction of high myopia with anterior chamber angle-supported phakic intraocular 

lenses—own results. [Article in Polish] Klin Oczna.

2003; 105(6):373-7.

306. Saxena R, Landesz M, Noordzij B, Luyten GP.

Three-year follow-up of the Artisan phakic intraocular lens for hypermetropia. Ophthalmol. Jul 

2003; 110(7):1391-5.

307. Zaldivar R, Davidorf JM, Oscherow S, Ricur G, et 

al. Combined posterior chamber phakic intraocular 

lens and laser in situ keratomileusis: bioptics for 

extreme myopia. J Refract Surg. May-Jun 1999; 

15(3):299-308.

308. Guell JL, Vazquez M, Gris O, De Muller A, et al.

Combined surgery to correct high myopia: iris claw 

phakic intraocular lens and laser in sit keratomileusis. J Refract Surg. Sep-Oct 1999; 15(5):529-37.

309. Fechner PU, Haubitz I, Wichmann W, Wulff K.

Worst-Fechner biconcave minus power phakic irisclaw lens. J Refract Surg. Mar-Apr 1999; 15(2):93-

105.

310. Leroux-Les-Jardins S, Ullern M, Werthel AL.

Myopic anterior chamber intraocular lens implantation: evaluation at 8 years. [Article in French] J Fr 

Ophthalmol. Apr 1999; 22(3):323-7.

311. Jimenez-Alfaro I, Benitez del Castillo JM, GarciaFeijoo J, Gil de Bernabe JG, et al. Safety of posterior 

chamber phakic intraocular lenses for the correction 

of high myopia: anterior segment changes after 

posterior chamber phakic intraocular lens implantation. Ophthalmol. Jan 2001; 108(1):90-9.

312. Pop M, Payette Y. Initial results of endothelial 

cell counts after Artisan lens for phakic eyes: an 

evaluation of the United States Food and Drug 

Administration Ophtec Study. Ophthalmol. Feb 

2004; 111(2):309-17.

313. Pesando PM, Ghiringhello MP, Tagliavacche P.

Posterior chamber collamer phakic intraocular lens 

for myopia and hyperopia. J Refract Surg. Jul-Aug 

1999; 15(4):415-23.

314. Arne JL. Phakic intraocular lens implantation versus 

clear lens extraction in highly myopic eyes of 30- to 

50-year-old patients. J Cataract Refract Surg. Oct 

2004; 30(10):2092-6.

315. Fink AM, Gore C, Rosen E. Cataract development 

after implantation of the Staar Collamer posterior 

chamber phakic lens. J Cataract Refract Surg. Feb 

1999; 25(2):278-82.

316. Brauweiler PH, Wehler T, Busin M. High incidence of cataract formation after implantation 

of a silicone posterior chamber lens in phakic, 

highly myopic eyes. Ophthalmol. Sep 1999; 

106(9):1651-5.

317. Allemann N, Chamon W, Tanaka HM, Mori 

ES, et al. Myopic angle-supported intraocular 

lenses: two-year follow-up. Ophthalmol. Aug 2000; 

107(8):1549-54.

318. Baikoff G, Arne JL, Bokobza Y, Colin J, et al.

Angle-fixated anterior chamber phakic intraocular 

lens for myopia of -7 to -19 diopters. J Refract Surg.

May-Jun 1998; 14(3):282-93.

319. Alio JL, de la Hoz F, Perez-Santonja JJ, Ruiz-Moreno 

JM, et al. Phakic anterior chamber lenses for the 

correction of myopia: a 7-year cumulative analysis 

of complications in 263 cases. Ophthalmol. Mar 

1999; 106(3):458-66.

320. Sippel KC, Jain S, Azar DT. Monovision achieved 

with excimer laser refractive surgery.Int Ophthalmol 

Clin. Spring 2001; 41(2):91-101.

321. Editor. Refractive surgery: Presbyopia reversal in 

pilot studies. Ocular Surgery News. Jul 1, 1999.

322. Nakagawara VB, Montgomery RW, Wood KJ.

Demographics and vision restrictions in civilian 

pilots: Clinical implications. Washington DC: 

Department of Transportation/Federal Aviation 

Administration. 2004 Report No. DOT/FAA/AM04/6.
37

323. Marmer RH. The surgical reversal of presbyopia: 

A new procedure to restore accommodation. Int 

Ophthalmol Clin. Spring 2001; 41(2):123-32.

324. Nataloni R. Refractive surgery: Presbyopia fix relies 

on radial incision in sclera. Ocular Surg News, Int 

Edition. Oct 1997.

325. Fukasaku H, Marron JA. Anterior ciliary sclerotomy 

with silicone expansion plug implantation: Effect on 

presbyopia and intraocular pressure.Int Ophthalmol 

Clin. Spring 2001; 41(2):133-41.

326. Thornton SP. Anterior ciliary sclerotomy (ACS), 

a procedure to reverse presbyopia. In Sher NA, 

ed. Surgery for hyperopia and presbyopia. Williams, 

Wilkins: Baltimore, MD, 1997, 33-6.

327. Editor. ASCRS 1999 maps new frontiers in refractive surgery. Primary Care Optom News. June 

1999.

328. Infrared Laser for Scleral Ablation for LAPR. At 

URL: www.surgilight.com/technology.html (Accessed 2/03).

329. Laser Presbyopia Reversal (LAPR). At URL: www.

iconimagecenter.com/laser-presbyopia-reversal.

html (Accessed 2/03).

330. Editor. FDA clears SurgiLight to initiate clinical 

trails of OptiVision laser. AOA News. January 13, 

2003; 41(13):9.

331. Nader N. Learning a new language: understanding the terminology of wavefront-guided ablation.

Ocular Surg News 2/1/03.

332. Alpins NA. Wavefront technology: A new advance 

that fails to answer old questions on cornea vs.

refractive astigmatism correction. J Refract Surg.

Nov-Dec 2002; 18(6):737-39.

333. Lipshitz I. Thirty-four challenges to meet before 

excimer laser technology can achieve super vision.

J Refract Surg. Nov-Dec 2002; 18(6):740-3.

334. CustomVue®. At URL: www.visx.com/index_

frame.php?section=customvue (Accessed 10/04).

335. Bausch, Lomb Zyoptix®. At URL: www.bausch.

com/us/vision/concerns/surgery/history.jsp (Accessed 10/04).

336. LADARVision®. At URL: www.ladarvision.

com/ladarvision/our_tracker_flash.asp (Accessed 

10/04).

337. Schonfeld D. Surgeon: Allegretto waver laser yields 

good results. Ocular Surgery News Europe/AsiaPacific Edition January 21, 2003.

338. Lawless MA, Hodge C, Rogers CM, Sutton GL.

Laser in situ keratomileusis with Alcon CustomCornea. J Refract Surg. Nov-Dec 2003; 19(6):

S691-6.

339. Boughton B. Allegretto laser works well for both 

hyperopia and myopia correction, says FDA trial 

data. EuroTimes. June 2003. At URL: www.escrs.

org/eurotimes/june2003/allegretto.asp (Accessed 

10/04).

340. Waheed S, Krueger RR. Update on customized 

excimer ablations: Recent developments reported in 

2002.Curr Opin Ophthalmol. Aug 2003; 14(4):198-

202.

341. Nuijts RM, Nabar VA, Hament WJ, Eggink FA.

Wavefront-guided versus standard laser in situ 

keratomileusis to correct low to moderate myopia.

J Cataract Refract Surg. Nov 2002; 28(11):1907-

13.

342. Kaiserman I, Hazarbassanov R, Varssano D, Grinbaum A. Contrast sensitivity after wave front-guided 

LASIK. Ophthalmol. Mar 2004; 111(3):454-7.

343. Shemesh G. Dotan G, Lipshitz I. Predictability of 

corneal flap thickness in laser in situ keratomileusis 

using three different microkeratome.J Refract Surg.

May-Jun 2002; 18(3): Suppl)S247-S51.

344. Gokmen F, Jester JV, Petroll WM, McCulley JP, et 

al. In vivo confocal microscopy through-focusing 

to measure corneal flap thickness after laser in situ 

keratomileusis. J Cataract Refract Surg. Jun 2000; 

28(6):962-70.

345. Ryne W. IntraLase creates consistently thin flaps.

Primary Care Optom News. March 1, 2004.

346. Kezirian GM, Stonecipher KG. Comparison of 

the IntraLase femtosecond laser and mechanical 

keratomes for laser in situ keratomileusis.J Cataract 

Refract Surg. Apr 2004; 30(4):804-11.

347. Binder PS. Flap dimensions created with the IntraLase FS laser. J Cataract Refract Surg. Jan 2004; 

30(1):26-32.

348. Ratkay-Traub I, Ferincz IE, Juhasz T, Kurtz RM, 

et al. First clinical results with the femtosecond 

neodynium-glass laser in refractive surgery. Refract 

Surg. Mar-Apr 2003; 19(2):94-103.
38

349. Xie RZ, Stretton S, Sweeney DF. Artificial cornea: 

towards a synthetic onlay for correction of refractive 

error. Biosci Rep. Aug 2001; 21(4):513-36.

350. Evans MD, Xie RZ, Fabbri M, Madigan MC, et al.

Epithelialization of a synthetic polymer in the feline 

cornea: A preliminary study. Invest Ophthalmol Vis 

Sci. Jun 2000; 41:1674–80.

351. Evans MD, Xie RZ, Fabbri M, Bojarski B, et al.

Progress in the development of a synthetic corneal onlay. Invest Ophthalmol Vis Sci. Oct 2002; 

43(10):3196-201.

352. Department of Transportation/Federal Aviation 

Administration: Guide for aviation medical examiners. Washington, DC:2005; FAA Office of 

Aerospace Medicine. Available at URL: www.faa.

gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/.

353. Nakagawara VB, Montgomery RW, Wood KJ. The 

aviation accident experience of civilian airmen with 

refractive surgery. Washington DC: Department of 

Transportation/Federal Aviation Administration.

2002. Report No. DOT/FAA/AM-02/10.

354. Surgical Eyes. At URL: www.surgicaleyes.com/ 

(Accessed 10/02).
A1

APPENDIX A. EYE 

Cornea 

APPENDIX A

The Eye

B

1

APPENDIX A 

REFRACTIVE SURGERY OPTIONS 

MYOPIA HYPEROPIA 

30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 10 

ICR

RK LTK

PRK

LASIK 

PHAKIC IOL PHAKIC IOL 

CLEAR LENS EXTRACTION CLEAR LENS EXTRACTON 

LEGEND ASTIGMATISM 

1 2 3 4 5 6 7 8 9 10 

 Ideal Range RK = Radial Keratotomy 

LTK = Laser Thermal Keratoplasty PRK

 Extended Range PRK = Photorefractive Keratectomy 

LASIK = Laser in situ Keratomileusis PRK

Phakic IOL = Phakic Intraocular Lens 

AK = Astigmatic Keratotomy LASIK

ICR = Intracorneal Ring 

APPENDIX B