bluuebunny/crossref_metadata_2025_split huggingface dataset:
Centration of Excimer Laser Photorefractive Keratectomy and Changes in Astigmatism
Authors: Aktunç Rengin , Aktunç Turgay 
Published: April 2021

ABSTRACT
One of the most important factors that influence the success of PKK might be corneal centration during treatment. We evaluated our centration rate in 49 eyes by using computer-assisted corneal topography. Only single zone treated eyes were chosen for the analysis and 91.5% of the eyes were centered within a 1 mm treatment zone while 51% were within 0.5 mm.
At the end of the follow-up time of 10.4 months, these centration zones were found to have no influence on the attempted spherical refractive outcome, whereas increasing decentration induced an increase in postoperative astigmatism. [J Refract Surg. 1996;12:S268-S271.]
Intrastromal Photorefractive Keratectomy for Myopia by Nd:YLF Picosecond Laser
Authors: Marchi Vincenzo , Gualano Antonio , Zumbo Giulio , Marchi Stefano 
Published: April 2021

ABSTRACT
BACKGROUND: An intrastromal photorefractive keratectomy (ISPRK) by Nd:YLF Picoseconds Laser has been performed on 17 eyes with corrected visual acuity of 20/200 or worse. The purpose of this study was to study the safety and effectiveness of ISPRK using different laser parameters.
METHODS: The Neodymiun Yttrium Lithium Fluoride laser system (Nd:YLF) was used to perform the myopic treatment. We studied the effect of pattern depth, the numbers of patterns, the thickness of a single spiral pattern, the distance between two patterns along Z axis, the pattern curvature perpendicular to the Z axis, the energy, the spatial density, and the repetition frequency of the laser pulse.
Assessment of Subjective Pain Following Photorefractive Keratectomy
Authors: McCarty Catherine A , Garrett Sinéad K M , Aldred Geoffrey F , Taylor Hugh R 
Published: April 2021

ABSTRACT
BACKGROUND: Although researchers have reported that postoperative pain in patients undergoing excimer laser photorefractive keratectomy (PRK) surgery is common in the first 24 hours after excimer surgery, factors associated with increased postoperative pain have not been reported. The purpose of this study was to prospectively document self-reported pain following excimer laser surgery and explore associated factors.
METHODS: Consecutive patients undergoing excimer laser photorefractive keratectomy (PRK) surgery to correct myopia and/or myopic astigmatism were asked to prospectively grade, on a fourpoint scale, the amount of pain they were experiencing immediately after treatment and again 2, 4, 8, 24, and 48 hours after surgery. They were also asked to record the type and dose of all medication taken during that time period.
RESULTS: Pain questionnaires were returned by 62 patients (72%), ranging in age from 20 to 54 years. The mean self-reported pain overall peaked 24 hours after treatment. Amount of myopia and prior excimer experience were not related to use of analgesia or self-reported pain (both p>0.10). Patients who had three additional topical drops of indomethacin postoperatively reported significantly less pain 24 hours after treatment (fc=5.95,p»0.0001).
CONCLUSION: These results have implications for the education of patients about the likely course of healing after PRK. A course of five drops of topical indomethacin should be evaluated with a randomized clinical trial to assess efficacy in inhibiting ocular pain after PRK. [J Refract Surg. 1996;12:365-369.]
The Effect of Various Methods of Eye Immobilization on Corneal Topography
Authors: Sher Neal A , Fundingsland Bradley A , Bergin Andrew , Burba Thomas , Forber Simon , DeMarchi Janet 
Published: April 2021

ABSTRACT
BACKGROUND: Accurate, predictable, and safe refractive surgery requires immobilization of the eye. We measured the effects of current eye fixation techniques on human cadaver eyes.
MATERIALS AND METHODS: Central to our study was a device specially designed to secure cadaver eyes and stabilize intraocular pressure. Topographical measurements were made with a modified Model 2 Corneal Analysis System (EyeSys Technologies, Houston, Tex) mounted vertically to allow analysis of a cadaver eye mounted in the artificial orbit. Ine effect on human cadaver eyes of six fixation instruments was assessed: forceps, U-shaped fixation forceps, a full Hofman-Thornton ring, a VISX vacuum fixation ring, a Méditée suction ring, and a new instrument, the Eye Fixation Speculum.
RESULTS: The circular vacuum fixation rings caused minimal distortion, resulting in less than 1.00 diopter (D) of change. Forceps and U-shaped fixation forceps, which apply force at one or two points, caused significantly more distortion. Single-point fixation forceps distorted the cornea at the point of application a mean of 4-5.50 ± 3.50 D, and, at 180° from the point of instrument application, a mean of 4-2.00 ± 1.90 D. U-shaped forceps apply force at two points, 90° and 270°, from the axis of instrument application. At these axes, the cornea was distorted a mean of +9.40 + 3.70 D and +8.30 + 3.10 D, respectively.
CONCLUSIONS: Single- and multi-point fixation instruments, due to an asymmetric application of fixation force, significantly distort the cornea. Ring fixation instruments, which apply a more equally distributed force, cause less distortion. [J Refract Surg. 1996;12:467-471.]
Relationships Between Preoperative Astigmatism and Corneal Optical Power, Axial Length, Intraocular Pressure, Gender, and Patient Age
Authors: Ninn-Pedersen Ken 
Published: April 2021

ABSTRACT
BACKGROUND: Preoperative astigmatism is likely to influence the outcome of cataract surgery, but it is only rarely considered in studies of cataract surgery outcomes.
METHODS: As part of a population-based study of 5878 consecutive cataract surgeries performed from 1986 through 1990, 1 studied the relationship between preoperative astigmatism and corneal shape, axial length, intraocular pressure, gender, and age.
RESULTS: The men had more against-the-rule astigmatism than the women, and the preoperative astigmatism shifted for both genders toward against-the-rule with age. Long eyes tended to have more with-the-rule astigmatism. Also, astigmatism deviated more from normal in both long and short eyes, and the with-the-rule astigmatism decreased with increasing intraocular pressure. Finally, I found that a second-degree polynomial model better described the relation between the axial lengths and keratometric powers better than a linear one.
CONCLUSIONS: Axial length is related to the direction and amount of astigmatism. Because in the present study a second-degree polynomial described the relationship between the axial lengths and keratometric powers better than a simple linear regression, a polynomial model also probably should be used for calculating the power of the intraocular lens to be inserted. [J Refract Surg. 1996;12:472-482.]
Assessment of Ablation Zone Centration After Photorefractive Keratectomy Using a Vector Center of Mass Formula
Authors: Almendral Dante , Waller Stephen G , Talamo Jonathan H 
Published: April 2021

ABSTRACT
BACKGROUND: Adequate centration of keratorefractive surgical procedures is essential for a successful outcome. An accurate technique to mathematically describe the centration and topography of the ablation zone after photorefractive keratectomy (PRK) would be valuable in assessing the effects of these variables on subsequent visual results.
METHODS: A vector center of mass formula and computerized videokeratography were used to study the postoperative treatment zone centration and topography of 17 consecutive highly myopic patients (-6.00 to 12.00 diopters [D]). Each had undergone PRK using either a single 6.0 mm (w=ll) or three-stepped ablation zone (n=6), with good visual results.
RESULTS: Calculations disclosed mean ablation zone deeentration relative to the pupil center for all patients to be 0.20 ± 0.16 mm using the vector center of mass formula. Areas of uniform central corneal dioptric power (mean diameter 3.4 ± 0.8 mm) and surrounding transition zones of declining dioptric power (mean slope 1.61 ± 0.44 D/mm) were also determined.
CONCLUSION: A new vector center of dioptric power distribution that analyzes centration and transition zone topography offers a rigorous but straightforward means to assess the effects of refractive corneal surgery procedures on central corneal topography. [JRefractSurg. 1996;12:483-491.]
Hexagonal Keratotomy-Should We Still Be Trying?
Authors: Werblin Theodore P 
Published: April 2021

ABSTRACT
BACKGROUND: I present my limited but positive experience with hexagonal keratotomy for hyperopia.
METHODS: Eighteen consecutive eyes of 12 patients underwent hexagonal keratotomy during 1993. In addition to the primary procedures, 14 enhancements were required in seven eyes for both astigmatism and undercorrection. Surgical planning was based on refractive data only. All surgeries were performed by one surgeon using the open hexagonal keratotomy pattern.
RESULTS: The patients' average age was 56 years (range, 38 to 67 years). Fourteen eyes were corrected for emmetropia. They had an average preoperative refraction of +2.22 + 0.64 diopters (D) and an average postoperative refraction of +0.11 ± 0.49 D. Four eyes were corrected for near vision (-2.00 D). They had an average preoperative refraction of -0.53 ± 0.83 D, and postoperatively their average refraction was -1.78 + 0.50 D. All four could read Jl without correction postoperatively. No eye lost more than one line of spectacle-corrected visual acuity; none had a major sight-threatening complication.
CONCLUSIONS: Hexagonal keratotomy can correct 3.50 D or less of hyperopia. Conservative surgery with one major reoperation procedure is suggested. Because of the highly variable results noted in the literature and several reports of significant complications, I no longer perform or recommend hexagonal keratotomy. [J Refract Surg. 1996;12:613-620.]
Histologic Changes and Wound Healing Response Following 10-Pulse Noncontact Holmium:YAG Laser Thermal Keratoplasty
Authors: Koch Douglas D , Kohnen Thomas , Anderson Janet A , Binder Perry S , Moore Max N , Menefee Richard F , Valderamma Giuseppe L , Berry Michael J 
Published: April 2021

ABSTRACT
BACKGROUND: Noncontact holmium:YAG laser thermal keratoplasty (Ho:YAG LTK) is a promising new technology for correction of hyperopia and astigmatism. We studied the acute histologic changes and wound healing response following Ho:YAG LTK performed with treatment parameters encompassing those used in clinical studies.
METHODS: We performed 10-pulse noncontact Ho:YAG LTK on three human corneas 1 day before their removal at penetrating keratoplasty and on six New Zealand white rabbit corneas followed for up to 3 months. Tissues were studied with light and transmission electron microscopy and immunohistochemistry.
RESULTS: The amount of acute tissue injury increased according to the pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death, loss of fine filamentous structure in Bowman's layer, disruption of stromal lamellae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbits included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation.
CONCLUSIONS: Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response. [J Refract Surg. 1996;12:621-634.]
Photorefractive Keratectomy for Hyperopic and Mixed Astigmatism
Authors: Dausch Dieter G J , Klein Robert J , Schröder Eckhard , Niemczyk Stephan 
Published: April 2021

ABSTRACT
BACKGROUND: The correction of astigmatism with photorefractive keratectomy has been recommended in simple and myopic astigmatism. Therefore in this study the excimer laser was used to correct compound hyperopic and mixed astigmatism.
METHODS: We present a prospective clinical study of photorefractive keratectomy in 30 eyes of 24 patients with compound hyperopic astigmatism with a mean spherical equivalent of +4.30 D and mean astigmatism of 2.33 D (group I) and in 17 eyes of 15 patients with mixed astigmatism with a mean spherical equivalent refraction of +0.46 D and mean astigmatism of 4.75 D (group II). The excimer laser used in this study was an MEL 60 (AesculapMeditec). In both groups an 18-month follow-up study was performed.
RESULTS: In the compound hyperopic astigmatism group after 18 months, 14 of 17 treated eyes (82.3 %) were within ±1.00 D, and 11 (64.7%) were within 60.50 D of the intended correction. In the mixed astigmatism group after 18 months, 10 of 11 eyes (90.9%) were within ±1.00 D, 8 eyes (72.7%) were within ±0.50 D of the intended correction. In regard to the stability the 1 year regression of spherical equivalent in the compound hyperopic astigmatism group is 0.78 D and in the mixed astigmatism group 0.37 D. At 18 months, spectacle corrected visual acuity in the compound hyperopic astigmatism group was unchanged or improved in 14 eyes (87.5%); 2 eyes (12.5%) had lost one line. In the mixed astigmatism group at 18 months, spectacle corrected visual acuity was unchanged or improved in 9 eyes (81.8 %); 2 eyes (18.1%) lost one line. Preoperatively, the mean uncorrected visual acuity was 20/100 in the compound hyperopic astigmatism group and the mixed astigmatism group. At 18 months, 14 eyes (93.3%) in the compound hyperopic astigmatism group had an uncorrected visual acuity of 20/40 or better; 4 (26.6%) eyes had an uncorrected visual acuity of 20/20 or better. In the mixed astigmatism group, 9 (81.8%) eyes had an uncorrected visual acuity of 20/40 or better; 4 (36.3%) eyes had an uncorrected visual acuity of 20/20 or better.
CONCLUSION: Photorefractive keratectomy is an efficient and relatively safe procedure for reducing or eliminating compound hyperopic and mixed astigmatism up to 6.00 D. [J Refract Surg 1996; 12:684-692.]
Four Techniques for Retreatment After Excimer Laser Photorefractive Keratectomy
Authors: Spadea Leopoldo , Bianco Guido , Balestrazzi Emilio 
Published: April 2021

ABSTRACT
BACKGROUND: Retreatment should be considered for patients unsatisfied because of undercorrection and/or haze following excimer laser photorefractive keratectomy (PRK) for myopia. It is unclear if any specific type of retreatment is superior to another, especially in terms of post-treatment myopic shift and haze.
METHODS: After a mean follow-up of 12.4 ±5.5 months, we retreated 10 eyes by four different techniques following failed PRK: only PRK, PRK with phototherapeutic keratectomy (PTK), only PTK, and mechanical scraping.
RESULTS: After a mean follow-up of 11.4±7.8 months (range, 6 to 28 mos), the final mean refraction was 2.40 ±2.00 D (range, 0 to -6.00 D). Corneal clarity improved in 70% of eyes. The mean uncorrected visual acuity improved from 20/200 to 20/40. Of the four retreatment techniques, only scraping proved ineffective, due to unstable outcome.
CONCLUSIONS: PRK alone, PRK with PTK, and PTK alone appeared safe and effective methods of retreatment, with no worsening of corneal clarity. [J Refract Surg 1996;12:693-696]
Management and Treatment of Central Steep Islands after Excimer Laser Photorefractive Keratectomy
Authors: Castillo Alfredo , Romero Francisco , Martin-Valverde Jose A , Diaz-Valle David , Toledano Nicolas , Sayagues Octavio 
Published: April 2021

ABSTRACT
BACKGROUND: Permanent central steep islands are an undesirable phenomenon that cause distorted images and a significant reduction in visual acuity. We describe treatment of central steep islands with repeat excimer laser photoablation in the central cornea.
METHODS: Three patients with preoperative refractions of -7.50 -2.50 x 170° D (right eye), -8.00 -2.25 x 10° D (right eye) and -6.00 -1.50 x 90° (right eye) developed central steep islands which persisted more than 12 months. All patients lost more than two lines of spectacle-corrected visual acuity and complained of visual disturbances. We retreated the central steep islands with a VISX 20/20 excimer laser PRK ablation that matched the size of the central island measured on videokeratography.
RESULTS: Symptomatic glare and distortion were significantly reduced and the central steep islands were resolved. Several weeks after reablation, spectacle-corrected visual acuity improved to the preoperative level.
CONCLUSION: Central steep island, an infrequent complication of excimer laser photorefractive keratectomy, can be safely removed with a repeat laser ablation that matches the central circular steep area. [J Refract Surg 1996;12:715-720.]
Corneal Ablation Profiles for Correction of Hyperopia with the Excimer Laser
Authors: Dierick Hans G , Missotten Luc 
Published: April 2021

ABSTRACT
PURPOSE: To calculate smooth corneal ablation profiles for the correction of hyperopia by means of excimer laser photorefractive keratectomy and to quantify the typical topographical changes, especially in the transition zone, in terms of axial distance and instantaneous radius of curvature.
METHODS: Conditions were determined to yield a smooth transition surrounding a hyperopic photorefractive keratectomy. Functions for the ablation depth in the transition zone were calculated. Theoretical optical zones of 4-mm diameter with 1 or 2-mm transition zones were required. The variation in axial and instantaneous power along one semimeridian was subsequently calculated. The power profile of a +10 diopters (D) correction on a spherical surface (47 D) was presented as an example for both ablation profiles.
RESULTS: In photorefractive keratectomy for hyperopia, the transition zone is necessarily flatter than the original cornea. The more abrupt the transition, the more pronounced the flattening. A central steepening of +10 D entailed a mid-peripheral flattening of -7.00 D or -15.00 D in transition zones of 2 and 1 mm width, respectively. In the transition zone, the mean rate of change of axial power was 15 and 45 D/mm, respectively.
CONCLUSION: Making the central cornea steeper by means of photorefractive keratectomy implies that the periphery should be flattened (axial power). The amount of flattening is directly proportional to the degree of steepening, and is relatively larger if the transition is more abrupt. [J Refract Surg 1996;12:767-7731
Diclofenac Sodium Attenuates Neural Activity after Photorefractive Keratectomy in Rabbits
Authors: Beuerman Roger W , McDonald Marguerite B , Zhang Daming , Varnell Ray J , Thompson Hilary W 
Published: April 2021

ABSTRACT
BACKGROUND: Photorefractive keratectomy for treating myopia has been associated with severe postoperative pain. The purpose of the present study was to investigate, in a rabbit model, the early effects of laser ablation on the physiology of the sensory nerves of the cornea.
METHODS: Neurophysiologic monitoring of the corneal nerves was carried out 4 to 6 hours after 5mm diameter, circular PRK ablations with a central depth of 85 µta. The effect of topical 0.1%, 0.25%, and 0.5% diclofenac sodium on the physiologic response to chemical and mechanical stimulation was evaluated. Corneas were prepared for anatomic studies of corneal innervation.
RESULTS: Heightened neural activity was observed in the corneal nerves after ablation, and exaggerated responses to sensory stimulation with hypertonic sodium chloride solutions were recorded. Diclofenac sodium at 0.1% decreased the response to 0.5 M NaCl and 0.7 M NaCl to 67 ± 9% and 68 ± 7% (mean ± standard error) of the control response. Mechanically sensitive nerves were more resistant to diclofenac; 0.1% diclofenac had no effect, but 0.25% diclofenac reduced the response significantly (P < 0.05). Anatomic observations showed that the ablation extended through the neural plexus. By 72 hours, long neurites tipped with growth cones had advanced into the injured region, indicating the initiation of neural regeneration.
CONCLUSIONS: Diclofenac sodium was effective in attenuating neural activity in the cornea after excimer laser ablation. The action of this agent was shown to be different from that of a topical anesthetic, which rapidly and totally inhibited the response to all forms of stimulation.
[J Refract Surg 1996;12:783-791]
Retrephination Keratoplasty for High Astigmatism after Penetrating Keratoplasty
Authors: Krueger Ronald R , Landry Robert J , Assil Kerry K , Schanzlin David J 
Published: April 2021

ABSTRACT
PURPOSE: We report preliminary results of a new procedure for correcting high astigmatism after penetrating keratoplasty.
METHODS: The procedure entails full-thickness trephination along the original donor-recipient junction with careful suturing in a combined interrupted and running fashion. Four eyes of four patients with severe astigmatism and myopia after penetrating keratoplasty underwent the procedure.
RESULTS: High preoperative cylinder ranging from 4.50 to 16.00 D (mean 9.00 D) was reduced to 0.50 to 3.50 D (mean 1.90 D) at the last examination (between 3 to 6 months). Spherical equivalent myopia ranging from -2.00 to -10.25 D (mean -4.90 D) was essentially unchanged at piano to -9.00 D (-4.70 D) at the last examination. Overall, there was a mean refractive cylinder reduction of 7.10 D (79%).
CONCLUSION: Retrephination after penetrating keratoplasty appears to be an acceptable alternative for correcting high astigmatism, and had only a small effect on the level of myopia. [J Refract Surg 1996;12:806-808]
Removal of Corneal Epithelium with Phototherapeutic Technique during Multizone, Multipass Photorefractive Keratectomy
Authors: Johnson Donald G , Kezirian Guy M , George Stan P , Casebeer J Charles , Ashton Jan 
Published: April 2021

ABSTRACT
BACKGROUND: The therapeutic mode of the VISX 20/20 excimer laser was used to remove the corneal epithelium prior to performing photorefractive keratectomy (PRK) with a multizone, multipass technique.
METHODS: A retrospective analysis was performed of 120 eyes of 90 patients that were treated for preoperative spherical refractive errors from -1.00 to -7.00 diopters (D) (mean -3.90 D, SD 1.54) by one surgeon (DGJ) over 7 months.
RESULTS: Six-month follow-up was obtained in 76 eyes (63%). Sixty-nine eyes (91%) achieved a spherical equivalent refraction within ±1.00 D of emmetropia. Regression of effect averaged -0.35 D (SD 0.53 D) from 1 to 6 months after surgery. Mean postoperative uncorrected visual acuity at 6 months was 20/25 (range 20/15 to 20/200). Seventythree eyes (96%) achieved uncorrected visual acuity of 20/40 or better, 67 (88%) achieved uncorrected visual acuity of 20/25 or better, and 76 (71%) achieved 20/20 or better. Three eyes (4%) lost one line of spectacle-corrected visual acuity; no eye lost more than one line. There were no significant surgical complications.
CONCLUSION: Removal of corneal epithelium with the Summit Excimed UV 200 LA excimer laser using multizone, multipass photoablation yields visual and refractive results that compare favorably with published PRK series with excellent short-term stability. [J Refract Surg 1998;14:38-48]