DOT/FAA/AM-00/19

Van B. Nakagawara

Kathryn J. Wood

Ronald W. Montgomery

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma 73125

May 2000

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

Refractive Surgery in Aircrew

Members Who Fly for Scheduled

And Nonscheduled Civilian Airlines

Office of Aviation Medicine

Washington, D.C. 20591

U.S. Department

of Transportation

Federal Aviation

Administration
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.
i

Technical Report Documentation Page

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

DOT/FAA/AM-00/19

4. Title and Subtitle 5. Report Date

May 2000 Refractive Surgery in Aircrew Members Who Fly for

Scheduled and Nonscheduled Civilian Airlines 6. Performing Organization Code

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

Nakagawara, V.B., Wood, K.J., Montgomery, R.W.

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

FAA Civil Aeromedical Institute

P.O. Box 25082

Oklahoma City, OK 73125 11. Contract or Grant No.

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

Office of Aviation Medicine

Federal Aviation Administration

800 Independence Ave, S.W.

Washington, D.C. 20591 14. Sponsoring Agency Code

15. Supplemental Notes

This work was performed under task AM-A-99-TOX-203.

16. Abstract

Introduction. Civil airmen with refractive surgery are present in all classes of aeromedical certificate holders.

Refractive surgical procedures have been associated with numerous side effects, including glare, reduced contrast

sensitivity, and fluctuating visual acuity. These side effects may render the quality of vision unacceptable in the

cockpit environment. This study reviews the aeromedical certification experience with refractive surgery in

aircrew members who fly for civilian airlines. Methods. Active airmen with FAA-specific pathology codes 130

(radial keratotomy) and 5179 (general eye pathology with surgical prefix) in the Consolidated Airman

Information System medical database during the period 1 January 1994 through 31 December 1996 were

identified. Airmen were stratified into those with a first-class medical certificate, an occupational code 1 (pilot,

copilot, first, and second officer) or code 2 (flight engineer), and an employer code of a scheduled or

nonscheduled airline. The medical records of these airmen were reviewed, and the clinical data were collated and

analyzed. Results. A total of 133 flight crewmembers (125 pilots and 8 flight engineers) were identified as

employees of airlines and having had refractive surgery. Seventeen airmen (12.8%) were miscoded and 2 airmen

(1.5%) were lost to follow-up. Of the 114 pilots with refractive surgery, 97 (85.1%) were incisional procedures,

15 (13.2%) were laser procedures, and 2 (1.7%) were complex surgical procedures. Three airmen (2.6%) had

serious complications resulting from the refractive procedure, including postoperative stromal haze, depth

perception problems, and a perforated cornea and crystalline lens resulting in a cataract. Conclusions. The

preponderance of aircrew members who have had refractive surgery and fly for scheduled or nonscheduled airlines

have incisional refractive procedures, which reportedly have the most critical visual side effects. A considerable

number of airmen have had laser procedures, of which the long-term effects are still unknown. Although some

serious complications have resulted from refractive surgery, the study indicates these complications have not

affected an applicant’s ability to receive an airman medical certificate.

17. Key Words 18. Distribution Statement

Aviation; Vision; Refractive Surgery; Aeromedical Document is available to the public through the

Certification; Occupational Health National Technical Information Service,

Springfield, Virginia 22161

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

Unclassified Unclassified 11

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

1

REFRACTIVE SURGERY IN AIRCREW MEMBERS WHO FLY FOR

SCHEDULED AND NONSCHEDULED CIVILIAN AIRLINES

INTRODUCTION

Refractive error is an optical defect that prevents

light rays from being focused as a clear, single image

on the retina. There are three types of refractive

conditions: myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (irregular cornea) (see

Figure 1). Approximately 55% of the U.S. population are dependent upon eyeglasses or contact lenses

to achieve a quality of vision satisfactory for their

daily needs (1). However, some individuals have

opted to use refractive surgery to free or reduce their

dependence on these traditional ophthalmic devices.

During the 1960s, complex surgical procedures,

such as keratomileusis and automated lamellar keratoplasty (ALK), were developed to correct refractive

error. Keratomileusis requires the removal of the

anterior two-thirds of the cornea with a microkeratome

(a specially designed scalpel). The corneal section

(lenticle) is then frozen and cryolathed according to

a computer program and resutured to the cornea bed

(2) (see Figure 2). With ALK, the microkeratome is

used to make a primary cap and a second shaping

resection (see Figure 2). The cap is then folded back

into position (3). Due to complications associated

with the sophisticated equipment, inherent

unpredictability with lenticle reshaping, individual

variability in healing, and the higher level of surgical

skill required, these procedures never gained widespread popularity (3,4).

Figure 1: The diagrams above illustrate the three most common forms of refractive error.

Hyperopia

(farsightedness)

Point

of Focus

Astigmatism

(irregular corneal curvature)

Points

of Focus

Lens

Cornea

Light

Rays

Fovea

Point

of Focus

Myopia

(nearsightedness)
2

Figure 2: The two diagrams on the left show the cornea in cross section after keratomileusis.

After reshaping to correct for myopia or hyperopia, the lenticle sections are returned to their

original positions in the cornea. The diagram on the right illustrates an ALK procedure. The

stromal tissue beneath the hinged corneal flap is removed prior to returning the flap to its original

position.

Keratomileusis

Hyperopic lenticle results

in corneal steepening

Myopic lenticle results

in corneal flattening

Automated Lamellar

Keratoplasty (ALK)

Secondary Resection

Corneal Cap

(flap)

Hinge

Photorefractive

Keratectomy (PRK)

Ablation Zone

Laser

Pulses

Radial Keratotomy (RK)

Radial Incisions

Laser-assisted in situ

Keratomileusis (LASIK)

Corneal Cap

(flap) Laser

Pulses

Hinge

Figure 3: The diagrams above illustrate the most common forms of refractive

surgery.
3

Radial keratotomy (RK) was first introduced in

the United States in the late 1970s and has been

performed on more than one million Americans (5).

The procedure consists of making incisions radially

on the peripheral cornea to a depth of 90-95% of the

corneal thickness, leaving the clear central optical

zone untouched (see Figure 3). These incisions weaken

the cornea and allow intraocular pressure to push the

peripheral cornea out, flattening the apex and reducing its refractive power (2). Patients with RK normally have stabilized vision within a week

post-operatively and minimal risk of vision loss from

surgical complications (8.3% mild and 0.3% severe

(6,7). When complications do occur, they include

decentered optical zone, monocular diplopia, traumatic rupture of keratotomy scars, endothelial cell

loss, delayed wound healing, over- or under-correction, induced astigmatism, glare disability, fluctuating acuity, reduced best corrected visual acuity

(BCVA), and diminished night vision (2,8,

9,10,11,12,13,14,15).

In October 1995, the Food and Drug Administration (FDA) approved the first excimer laser to be used

for photorefractive keratectomy (PRK). Since then,

PRK and a modified form of this procedure, known

as laser-assisted in situ keratomileusis (LASIK), have

quickly become the refractive surgical procedures of

choice. PRK utilizes the excimer laser light to ablate

(remove) tissue from the surface of the cornea, reducing its curvature and minimizing or eliminating

myopia (see Figure 3). Following PRK, it can take

several days for vision to improve, and most patients

become slightly overcorrected for a few weeks before

their vision begins to stabilize. The time required for

a patient’s vision to stabilize ranges from 3 to 6

months for low myopia and 6 to 18 months for high

myopia (16). For most PRK patients, clinical studies

have shown excellent refractive stability 1 to 2 years

after surgery, with re-treatment rates ranging from

0.64 to 9.1% (17,18). At 3 years, post-operative

uncorrected visual acuity of 20/40 or better was

found in 83% of eyes (19). PRK complications are

infrequent but may include delayed healing, overcorrection, corneal scarring, myopic regression, glare/

halos, loss of BCVA, decreased contrast sensitivity,

night vision problems, and corneal haze (16,20,

21,22,23,24).

The LASIK procedure is performed using the

excimer laser and microkeratome. The microkeratome

slices a thin horizontal flap from the anterior cornea,

leaving it connected by a small hinge of tissue. The

flap is folded aside and the laser ablates tissue from

the cornea’s stromal bed, and the flap is then replaced

(25) (see Figure 3). LASIK has significantly less

corneal scarring and regression, since the Bowman’s

layer (membrane between the epithelium and stroma)

of the cornea is not ablated (26). Typically, LASIK

patients experience less pain, stabilize faster, and do

not require extended use of topical steroids, compared with PRK patients (26). LASIK complications

include loss of BCVA, irregular astigmatism, regression, and night vision problems (27,28,29,30). However, unlike PRK, LASIK can have surgical

complications including interface deposits, shifted

or lost corneal flap, minor corneal bleeding, and

improperly set microkeratome depth resulting in too

thin of a corneal flap or perforated cornea (28,31,32).

Civil airmen with refractive surgery are present in all

classes of aeromedical certificate holders. It is estimated

that one million laser refractive surgical procedures will

be performed annually in the U.S. in the year 2000.

Refractive surgical procedures have been associated

with numerous visual side effects that may render the

quality of vision unacceptable in the cockpit environment. This report reviews civil aeromedical certification

experience with refractive surgery for the study period

1994-96. It specifically examines the frequency and

type of refractive surgery performed on crewmembers

who fly for scheduled and nonscheduled airlines.

METHODS

1. A list of all active airmen who carried Federal

Aviation Administration (FAA)-specific pathology codes 130 (radial keratotomy) and 5179 (general eye pathology with surgical prefix), during

the period 1 January 1994 through 31 December

1996, was generated from the FAA’s Consolidated Airman Information System medical database.

2. The general eye pathology code 5179 is assigned

to applicants with various types of eye surgeries. A

medical record review identified those airmen

who carried pathology code 5179 that had refractive surgery. These airmen and those with pathology code 130 were then collated into a common

database.
4

3. First-class medical certificate holders who had an

occupational code 1 (captain, co-pilot, and first

and second officers) or occupational code 2 (flight

engineers), indicating they worked for a scheduled and nonscheduled airline, were identified

and their medical records examined. The clinical

data were collated into a second database and

analyzed.

RESULTS

A total of 133 airline crewmembers (first-class

medical certificate holders with occupational code 1

or 2) who had refractive surgery were identified by

pathology codes (see Table 1). A review of the medical records revealed that 17 airmen (12.8%) were

miscoded. Interestingly, 7 of those miscoded airmen

were using contact lenses for orthokeratology (i.e.,

contact lenses used to alter the curvature of the cornea

and reduce myopia). Two of the 133 medical records

(1.5%) were lost to follow-up. The remaining 114

airmen (85.7%) were found to have undergone refractive surgery. Of these, 97 airmen (85.1%) had

incisional procedures, 15 (13.2%) had laser

procedures, and 2 (1.7%) had a complex surgical

procedure (i.e., ALK). Three airmen (2.6%) had

serious complications from their refractive procedure, including postoperative stromal haze after PRK,

a perforated cornea and crystalline lens resulting in a

cataract after LASIK, and depth perception problems

after RK.

Since a physical review of all medical records for

aviators with pathology code 130 was not practical,

demographic statistics from this sample airline

crewmember population (n = 132) were applied to

those airmen who carried pathology code 130 for the

study period 1994-96 (n = 3,712). To estimate the

total number of airmen with refractive surgery, those

with pathology code 5179 (n = 50) were then reintroduced to the estimated 130 group (n = 3,761). The

total estimated refractive surgery population included

2,735 airmen with incisional procedures (RK), 436

airmen with laser refractive procedures (372 with

PRK and 64 with LASIK), and 56 airmen with other

complex refractive procedures (e.g., ALK), while 478

were miscoded, and 56 records were non-retrievable

(see Figure 4).

Types of Refractive Surgery and Complications in First-Class, Code 1 & 2 Airmen

PROCEDURE COMPLICATION DESCRIPTION CODE 1 CODE 2 TOTAL

PRK STROMAL HAZE (n = 1, CODE 1) 11 2 13

LASIK PERFORATED CORNEA (n = 1, CODE 1) 1 1 2

ALK 2 2

RK DEPTH PERCEPTION PROBLEMS (n = 1, CODE 1) 93 4 97

TOTAL 107 7 114

MISCODED 16 1 17

RECORDS LOST TO FOLLOW-UP 2 2

TOTAL PROCEDURES 125 8 133

Table 1: Results from the review of medical records of all airline crewmembers (1994-96) that held first-class

medical certificates with pathology codes for refractive surgery are identified by type of refractive procedure and

occupation code.
5

DISCUSSION

Optimum vision is essential for pilots who must

detect and identify airborne traffic as well as hazards that

may be on runways and taxiways. Printed material such

as flight manifests, charts and maps, and cockpit instruments need to be clearly visible to ensure that proper

flight procedures are safely followed. Therefore, a pilot’s

choice of refractive correction can affect his/her ability

to efficiently perform critical operational activities. The

vast majority of pilots who require refractive correction

opt for eyeglasses or contact lenses. However, for some

aviators who depend on these traditional forms of

correction, the cockpit environment can exacerbate

what would normally be minor difficulties outside the

cockpit. Spectacle frames can reduce the field of vision,

be uncomfortable when not properly fitted, become

displaced during flight maneuvers, and are often incompatible with communication and protective breathing

equipment. Spectacle lenses may also be dislodged and

fogging can occur with changes in air temperature and

humidity. Contact lenses have been displaced and even

lost in flight, and airmen have reported removing

contact lenses in flight, primarily for dryness or a

foreign body beneath the lens. The low barometric

pressure and low relative humidity (10-15%) of an

aircraft at altitude can affect contact lens wear. Soft

contact lenses dehydrate in low humidity and may

result in visual performance loss (low-contrast acuity).

In addition, low humidity can reduce lens movement

Figure 4: The chart represents the estimated number of aviators in the civil airman population (1994-96)

that have various types of refractive surgical procedures. The estimate is based on applying the

percentages found in the review of airline crewmembers to the total number of aviators that carried

pathology codes for refractive surgery and general eye surgery during the study period.
6

and increase conjunctival injection (redness) in contact

lens users, indicating a tighter fit. Finally, corneal edema

has been reported in seemingly well-fit contact lens users

with altitude hypoxia.

Airline crewmembers, who are first-class medical

certificate holders with occupational code 1 or code

2 designations, must past the most stringent vision

standards of all 3 classes of FAA medical certificates

and are examined more often (every 6-months) to

maintain their flying status. Currently, all applicants

with refractive surgical procedures may obtain a

medical certificate without a waiver if they meet the

visual acuity standards for the class of medical certificate requested. However, these applicants are required

to submit verification from an eyecare specialist that

their vision is stable, healing is complete, and that no

increased glare sensitivity is present.

The majority (85.1%) of airline crewmembers

with refractive eye surgery had incisional refractive

surgery (RK). The ophthalmic literature suggests that

this procedure is more frequently associated with

visually compromising side effects (10,14,15). About

13.2% of airline crewmembers had laser refractive

procedures (PRK = 13 and LASIK = 2). Since the

excimer laser used to perform refractive surgery was

not approved by the U.S. Food & Drug Administration (FDA) until October 1995, this suggests that

aviators had their procedures performed in other

countries or as a part of the original FDA clinical

trials. In our population, only 2.63% reported serious visual side effects attributable to their refractive

procedures. Fortunately, these complications did not

affect their ability to obtain an aeromedical certificate and continue their aviation careers.

There are several important factors regarding refractive surgery that may increase the risk of operational errors for aviators. These include:

n The long-term effects of laser refractive surgery

techniques are unknown. Aviators often continue to fly professionally and/or privately for

decades. Normal age-related changes in vision

performance might be exacerbated by these procedures. Younger pilots may choose refractive surgery to satisfy aeromedical vision standards and to

qualify for low-cost pilot training (e.g., school

programs, civilian employers).

n The quality of vision that results from refractive

surgery may be compromised. Although the highcontrast Snellen visual acuity test used in aeromedical certification examinations may be normal

after refractive surgery, results from more sensitive measures of vision performance, such as glare

or contrast sensitivity tests, are often abnormal.

n Unequal refractive surgery is used on some patients to induce monovision for the correction of

presbyoia. Monovision (one eye corrected for

distance and one eye for near) is often performed

using refractive surgery (33,34). The effect of

monovision refractive surgery may result in additional operational errors (Note: Monovision contact lenses were found to be a causal factor in an

airline accident (35).). Currently the “Guide for

Aviation Medical Examiners” states that “the use

of a contact lens in one eye for distant visual

acuity and a lens in the other eye for near visual

acuity is not acceptable (36).”

n The compatibility of refractive surgery to the

aviation environment has not been fully investigated. Rapid acceleration and deceleration, lower

relative humidity and oxygen levels, decompression, and increased cosmic and ultraviolet radiation may affect the surgically altered corneal tissue.

Future use of high-altitude civil transport aircraft

may further increase these environmental stresses

on the pilots’ vision.

In conclusion, the majority of aircrew members with

refractive surgery who fly for airlines have had incisional

refractive procedures, which are associated with more

visual side effects. However, this study found a low

complication rate and no reported aeromedical certification problems with incisional refractive surgery. There

were a considerable number (13.2%) of aircrew members with laser refractive surgery procedures (e.g., PRK,

LASIK), for which the long-term effects are still unknown. The number of such procedures is expected to

increase significantly in the future. Although there were

airmen who reported serious complications resulting

from these types of refractive surgery, this study indicates these complications have not affected the airman’s

ability to obtain an aeromedical certificate. Additional

research is recommended to evaluate the effects of

aviation environmental stressors on the visual performance of pilots with laser refractive surgery.
7

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