bluuebunny/crossref_metadata_2025 huggingface dataset:
Aspheric Photorefractive Keratectomy With Excimer Laser
Authors: Seiler Theo , Genth Uwe , Holschbach Andreas , Derse Matthias
Published: April 2021

ABSTRACT

BACKGROUND: Increased spherical aberration of the cornea is a common finding after excimer laser keratorefractive keratectomy. The shape of the paracentral cornea is probably related to the incidence of side effects like glare and halos at night depending on ablation zone size and pupil diameter. Aspheric curvature changes of the paracentral cornea at the edge of the ablation may decrease those side effects.

MATERIALS AND METHODS: Fifteen patients were treated with photorefractive keratectomy for myopia correction with a Summit excimer laser (Summit Technology, Waltham, Mass), one eye using a standard spherical algorithm and the fellow eye using a new aspherical algorithm. Eyes were followed for 6 to 18 months.

RESULTS: None of 15 patients reported halos in the aspherically corrected eye stronger than in the fellow eye, whereas five patients claimed stronger halos in the spherically corrected eye. The effective clear zone size was 3. 16 ± 0.35 mm in the spherical cases compared to 3.43 ± 0.31 in the aspherical cases, although the same ablation zone diameters of 5 mm were used. This difference is highly statistically significant. Effective spherical aberration based on raytracing analysis of the central 5 mm of the corneal topographic maps was significantly smaller in the corneas with aspheric correction than in those with spheric corrections.

CONCLUSION: These results indicate better optical homogeneity in eyes after aspheric photorefractive keratectomy for myopia compared to standard spherical corrections. (Refract Corneal Surg. 1993;9:166-172.)

RÉSUMÉ

INTRODUCTION: Une augmentation dans l'écart sphérique de la cornée suit souvent la kératectomie photorefractive au laser excimer. La forme de la cornée paracentrale a probablement un rapport avec les effets secondaires comme Péblouissement et les halos nocturnes, selon la taille de la zone d'ablation et la diamètre de la pupille. Il est possible que des changements asphériques dans la courbure cornéenne puissent réduire ces effets secondaires.

METHODS: Quinze patients ont subi la kératectomie photorefractive démyopisante avec le laser excimer de Summit (Waltham, Mass), une oeil selon un algorithme sphérique ordinaire et l'autre selon l'algorithme asphérique nouveau. Le suivi variait de 6 à 18 mois.

RÉSULTATS: Aucun des 15 patients n'a indiqué de halos plus forts dans l'oeil opéré asphériquement que dans l'autre oeil, tandis que cinq patients ont rapporté des halos plus forts dans l'oeil sphériquement corrigé. La taille e la zone claire effective était de 3, 16 ±0,35 mm dans les cas sphériques par comparaison avec 3,43±o,31 dans les cas asphériques, bien qu'on ait utilisé le même diamètre de la zone d'ablation, 5 mm. Cette différence est statistiquement très significative. L'écart sphérique réel, basé sur l'analyse de la recherche des rayons pour les 5 mm qui forment le centre de la cornée était beaucoup plus petit chez les patients à la cornée à correction asphérique que chez ceux dont la correction est sphérique.
Computer Program to Calculate Vectorial Change of Refraction Induced by Refractive Surgery
Authors: Calossi Antonio , Verzella Franco , Penso Andrea
Published: April 2021

ABSTRACT

BACKGROUND: After refractive surgery, there may be changes in the spherical and the cylindrical components of the ametropia. In astigmatism, there may be variations in both the power and the axis. The best way to describe change in astigmatism caused by surgery is by vectorial analysis, which Indicates the changes in power and the axis. However, In clinical practice, this procedure is limited by the tedious calculations required to establish the oblique cylinder combinations.

METHODS: We propose a computer program for the calculation, by vectorial analysis, of the refractive changes induced by surgery. The program allows for reference to refractive data or keratometric readings. When the refractive data are considered, it is also possible to obtain the transposition of the correction values from the spectacle plane to that of the cornea. Finally, the program enables the user to calculate the coupling ratio.

RESULTS: Some selected surgical cases are discussed by way of example.

CONCLUSIONS: We think that this program will be a simple and accurate means of evaluating the results of refractive and corneal surgery. (Refract Corneal Surg 1993;9:276-282.)

RESUMÉ

INTRODUCTION: Suivant la chirurgie refractive il peut exister des changements dans les éléments sphériques et cylindriques de l'amétropie. L'analyse vectorielle, qui indique les changements dans la pouvoir et l'axe de l'astigmatisme, est la meilleure façon de décrire ces effets. Néanmoins, les calculs ennuyeux qu'il faut pour établir les combinaisons de cylindres obliques sont peu pratiques en clinique.

METHODES: Nous proposons un programme informatique pour calculer par l'analyse vectorielle les changements réfractifs induits par la chirurgie. Le programme permet d'obtenir des références aux données réfractives et kératométriques. En utilisant les données réfractives on peut transposer la correction optique du plan des lunettes jusqu'à la corneé. Finalement, le programme permet calcul du rapport de couplage.

RÉSULTATS: Nous discutons de quelques malades choisis.

CONCLUSIONS: Nous espérons que ce programme informatique soit un moyen simple et précis afin d'évaluer les résultats des chirurgies cornéennos et réfractives. (Translated by Rob Mack, MD, Iowa City, la.)

SOMMARIO

PREMESSA: Dopo un intervento di chirurgia refratfrva si possono avere variazioni della componente sferica e di quella cilìndrica dell'ametropia. Per quanto riguarda l'astigmatismo, le variazioni si possono avere sia nel potere che nell'asse. Il modo più corretto per descrivere la variazione dell'astigmatismo indotta dalla chirurgia è l'analisi vettoriale, che Indica la variazione sia del potere che deìVasse. D'altra parte nella pratica clinica questa procedura è limitata dalla complessità dei calcoli necessari a risolvere (a combinazione di cilindri obliqui.
Assessing the Efficacy of Topical Corticosteroids Following Radial Keratotomy
Authors: Haverbeke Luc
Published: April 2021

ABSTRACT

BACKGROUND: The postoperative use of topical corticosteroids may decrease the risk for regression and thereby improve the refractive outcome following radial keratotomy.

METHODS: Twenty patients with identical preoperative refractions in each eye underwent bilateral radial keratotomy in one sitting. One eye was treated with dexamethasone twice daily for 3 months postoperatively; the fellow eye was not.

RESULTS: Three months postoperatively, there was no difference between the refractions of the two groups of eyes.

CONCLUSION: The use of topical dexamethasone after radial keratotomy for 3 months does not improve the refractive outcome, [Refract Corneal Surg 1993;9:379-382.)
Radial Keratotomy Does Not Affect Intraocular Pressure
Authors: Sastry Srinivas M , Sperduto Robert D , Waring George O , Remaley Nancy A , Lynn Michael J , Blanco E , Miller David N
Published: April 2021

ABSTRACT

BACKGROUND: Recent reports have suggested that a secondary effect of radial keratotomy may be a reduction in intraocular pressure (IOP) levels.

METHODS: In an effort to study the relationship of radial keratotomy to IOP, we compared the mean IOP from the baseline and follow-up visits during 1 year after surgery of operated versus nonoperated eyes of patients enrolled in the Prospective Evaluation of Radial Keratotomy (PERK) study. To investigate if radial keratotomy had more of an effect on eyes with higher baseline IOPs, the same analysis was performed on a subset (134 patients) who had a baseline IOP of 15 mm Hg or greater.

RESULTS: The average baseline IOP for both operated eyes and nonoperated eyes was 14.6 mm Hg. There was no significant difference in mean IOP between operated and nonoperated eyes across all time points (p=.18). Although mean IOP changed over time, it did not clinically differ in operated versus nonoperated eyes at any time point. These findings were similar in the analysis of eyes with higher baseline IOP (15 mm Hg or greater).

CONCLUSION: We conclude that the radial keratotomy performed in the PERK study had no effect on IOP within 1 year after surgery. (Refract Corneal Surg. 1993;9:459-464.)

RÉSUMÉ

INTRODUCTION: Plusieurs rapports ont suggéré que la kératotomie radiaire peut réduire la pression jntraoculalre comme effet secondaire.

MÉTHODES: Afin d'étudier les effets de la kératotomie radiaire vis à vis de la pression întraoculaire nous avons comparé la pression moyenne întraoculaire lors de la première visite avec les pressions mesurées pendant une année en suite post-opératoire sur les yeux opérés et les yeux non-opérés chez les patients dans L'Etude Prospective de la Kératotomie Radiare (PERK, en Anglais). Pour déterminer l'effet de la kératotomie radiaire sur les yeux avec une pression plus haute avant traitement, ia même analyse fut utilisée chez 134 patients avec une pression d'au moins 15 mm Hg.

RÉSULTAT: La pression moyenne întraoculaire chez les yeux opérés et les yeux non-opérés était de 14,6 mm Hg. Il n'existait à aucun moment une différence significative dans la pression moyenne întraoculaire entre les yeux opérés et les yeux non-opérés (p=0,18). Quoique la pression moyenne întraoculaire variait avec le temps, elle n'a jamais changé entre les yeux opérés et les yeux non-opérés. Les résultats furent similaires avec les yeux ayant une pression plus élevée au début r>15mmHg).

CONCLUSION: Nous concluons que la kératotomie radiaire dans l'étude PERK n'a eu aucun effet sur la pression întraoculaire post-opératoire. (Translated by Robert Mack, MD, Iowa City, la.)
Lamellar Keratoplasty for Hyperopia
Authors: Manche Edward E , Judge Anisha , Maloney Robert K
Published: April 2021

ABSTRACT

PURPOSE: Lamellar keratoplasty for hyperopia (automated lamellar keratoplasty for hyperopia) can correct hyperopia by weakening the cornea with a deep lamellar resection. The safety and efficacy of the procedure is uncertain.

METHODS: Twenty-four eyes of 17 patients underwent hyperopic lamellar keratoplasty using the automated corneal shaper (Chiron Corp, Irvine, Calif) by one surgeon using a flap technique. The mean attempted correction was +3.90 ± 0.90 D (range, +2.00 to +6.00). The eyes were followed for 1 month (23 eyes) to 6 months (17 eyes).

RESULTS: Six months after hyperopic lamellar keratoplasty, the mean difference between attempted and achieved correction was an undercorrection of +1.40 ± 0.80 diopters (D) with 7 of 17 eyes within 1.00 D of the attempted correction. No eyes were overcorrected, and 15 eyes were undercorrected. In eyes with a refractive goal of emmetropia, uncorrected visual acuity was 20/40 or better in 13 of 15 eyes and 20/20 or better in 8 of 15 eyes. No eye lost two or more lines of spectacle-corrected visual acuity at 3 or 6 months postoperatively. Between 1 and 6 months, there was a mean hyperopic shift of 0.20 D. There was clinically significant epithelial ingrowth into the interface in two eyes.

CONCLUSION: Hyperopic lamellar keratoplasty is an effective method of reducing hyperopia and induces little irregular astigmatism. The nomogram we used produces a consistent undercorrection. Refraction appears to stabilize at 1 month, but longer follow up is necessary to assess stability. [J Refract Surg. 1996;12:42-49.]
Keratocyte-Populated Collagen Gel as an In Vitro Model of Excimer Laser Keratectomy
Authors: Wee Won Ryang , Nassaralla Belquiz A , Garbus Jenny , McDonnell Peter J
Published: April 2021

ABSTRACT

BACKGROUND: To develop an in vitro model to study the effects of excimer laser keratectomy on corneal stromal cells, we evaluated two types of collagen gel populated with keratocytes.

METHODS: Keratocyte-populated collagen gels were prepared with type I collagen in 6-well plates or in culture plate inserts, the bottom of which consisted of a nitrocellulose membrane, contained within 6-well plates. The gels were ablated by the 193-nm excimer laser, set to ablate 50, 100, or 200 µm deep, and was observed under a phase-contrast microscope for 2 days.

RESULTS: Keratocytes cultured in collagen gel developed cytoplasmic processes and formed networks of interconnected cells. Cells within the ablated area in the 6-well plates began to lose their cytoplasmic processes and became round approximately 3 hours after excimer laser ablation. These cellular changes were more prominent in the gels ablated to a depth of 200 µm. Cells outside of the ablation zones ill the 6-well plates and the culture plate inserts remained intact.

CONCLUSIONS: These results suggest the use of keratocyte-populated collagen gel as an in vitro model of cellular response to excimer laser keratectomy and also suggest that gel prepared in culture plate inserts is the preferred method. [J Refract Surg. 1996;12:98-102.]
Phototherapeutic Keratectomy for Climatic Droplet Keratopathy
Authors: Badr Ihsan A , Al-Rajhi Ali , Wagoner Michael D , Dunham Timithy , Teichmann Klaus D , Cameron James A
Published: April 2021

ABSTRACT

BACKGROUND: Phototherapeutic keratectomy (PTK) is an effective treatment for many superficial corneal disorders. The efficacy of PTK for the treatment of climatic droplet keratopathy (CDK) has not been reported.

METHODS: We report the results of excimer laser (Summit Technology, Inc, Waltham, Mass) PTK on 75 eyes (67 patients) with "smooth" climatic droplet keratopathy (55 eyes) and "irregular" climatic droplet keratopathy (20 eyes) in whom more than 6 months of follow up are available.

RESULTS: PTK was successful in reducing corneal opacification in both smooth (98%) climatic droplet keratopathy and irregular (80%) climatic droplet keratopathy. Achievement of a clear or mildly hazy cornea following PTK was more likely to occur with smooth (80%) climatic droplet keratopathy than irregular (25%) climatic droplet keratopathy (P=0.01). Eyes with smooth climatic droplet keratopathy were more likely to obtain more than one line of improved uncorrected (56% vs. 25%) or spectacle-corrected visual acuity (61.8% vs. 21.2%) than those with irregular climatic droplet keratopathy (P=0.03 and 0.005, respectively). Delayed re-epithelialization (longer than 14 days) was more common in irregular CDK (21%) than in smooth CDK (9%), as was the incidence of secondary microbial keratitis (10.0% vs. 1.8%).

CONCLUSIONS: PTK is effective in reducing superficial corneal opacification in CDK, although serious complications may occur, especially in advanced irregular CDK. [J Refract Surg. 1996;12:114-122.]
Eye Infections After Refractive Keratotomy
Authors: Jain Sandeep , Azar Dimitri T
Published: April 2021

ABSTRACT

BACKGROUND: Ocular infections are serious and potentially vision-threatening complications of refractive keratotomy. We have performed an integrative review of published literature to address important issues concerning these complications.

METHODS: Articles in MEDLINE and published manuscripts and abstracts reporting previously unpublished cases of infections after refractive keratotomy were systematically identified and reviewed. Our review did not target patients treated with relaxing incisions for postkeratoplasty astigmatism. Pertinent data were abstracted and analyzed.

RESULTS: Forty-three cases (47 episodes: 42 keratitis and 5 endophthalmitis) of infection appeared in 26 published reports from 1975 to 1994. The frequency ranged from 0.25% to 0.70%. In 22 (47%) eyes, infection occurred before 2 weeks. Thirty-five (74%) infections were located in the inferior half of the cornea, and 22 (62%) were located in the inferotemporal quadrant. Thirty-one (66%) infections were bacterial (32% gram-positive, 23% gram-negative, 9% acid fast, 496 unknown), 5% fungal, 6% viral, 19% sterile, and 4% of unknown origin. Spectacle-corrected visual acuity after conservative treatment was 20/40 or better in 70% of eyes. Penetrating keratoplasty was performed in six cases. Potential associations included reoperations in 12 (26%) eyes, postoperative contact lens wear in 7 (15%), and intraoperative perforation in 7 (15%).

CONCLUSIONS: The published literature indicates that infections after refractive keratotomy may compromise visual function. Approximately half of the infections occur in the first 2 weeks. Reoperations, postoperative contact lens wear, and intraoperative perforations may be significant risk factors. [J Refract Surg. 1996;12:148-155.]
Videokeratography of Keratoconus in Monozygotic Twins
Authors: Parker James , Ko William W , Pavlopoulos George , Wolfe Peter J , Rabinowitz Yaron S , Feldman Sandy T
Published: April 2021

ABSTRACT

PURPOSE: To determine the corneal topographic appearance in a pair of monozygotic twins and family members of the twins because one of the twins had keratoconus and the other appeared normal by clinical examination.

METHODS: Clinical examination and videokeratography (Topographic Modeling System, Tomey) of the patient, his monozygotic twin brother, an older brother, and his parents were performed. The I-S values (difference in the average dioptric powers of symmetrical points between the inferior and superior cornea) were calculated.

RESULTS: The patient, a 28-year-old man, had clinical keratoconus confirmed with videokeratography. Clinical examination of family members including a twin brother, an older brother and both parents revealed no corneal abnormalities. Videokeratography of the clinically normal twin brother showed inferior steepening with progression over time. The I-S value of the clinically normal brother was 1.36 (right eye) (greater than 2.00 SD of normal controls), which progressed to 1.69 (right eye), 1.32 (left eye) 5 months later and to 1.87 (right eye), 1.43 diopters (D) (left eye) 14 months later. Minimal asymmetric inferior steepening was noted in an older brother who had an I-S value of 0.81 (right eye), 1.27(left eye). The mother appeared topographically normal.

CONCLUSIONS: This study lends support to the existence of subclinical keratoconus detectable by videokeratography only. [J Refract Surg. 1996;12:180-183.]
From the Sponsors
Authors: Frey Randy , Martin Steve
Published: April 2021

Editorials
Early Results of Photorefractive Keratectomy for Myopic Astigmatism
Authors: Kaskaloglu Mahmut
Published: April 2021

ABSTRACT

BACKGROUND: The Technolas Keracor 116 excimer laser has been used to correct myopic astigmatism. The purpose of this study was to evaluate the early results in our patients.

METHODS: The Technolas Keracor 116 excimer utilizes a scanning beam to correct myopic astigmatism. Following the correction of the astigmatic error, spherical myopic component is then treated. Twenty-eight eyes with myopic astigmatism were treated utilizing a 4 x 12 mm ablation zone for astigmatism and 4.5 nun to 6.6 mm transition zone for the spherical component at the same session. The mean preoperative spherical equivalent refraction was -4.87 ± 3.48 diopters (D) (range: -1.00 to -14.25) and the mean preoperative astigmatic error was -2.53 ± 1.49 D (range: -1.00 to -6.00 D) All eyes received dexamethasone eye drops for 3 months.

RESULTS: At 6 months, the mean spherical equivalent refraction was +0.23 D (range +1.38 to -1.50 D), the mean postoperative refractive cylinder was -0.16 ± 0.99 D (range: +1.50 to -2.00 D) and 78% of the eyes had a refraction within ± 1 D. Fifty-five percent achieved 20/40 or better uncorrected visual acuity. In three cases there was one line loss and in two cases there was two line loss in best corrected spectacle visual acuity.

CONCLUSIONS: Early results from this study suggest that excimer laser photorefractive keratectomy effectively reduces myopic astigmatism. The treatment of astigmatism offers a new challenge for excimer laser corneal surgery. Lasers utilize different methods to control the beam that reshapes the cornea.1-5 [J Refract Surg. 1996;12:S258-S260.]
Photorefractive Keratectomy With a Transition Zone for Myopia from -7 to -14 Diopters
Authors: Siganos Dimitrios S , Pallikaris loannis G , Margaritis Vasilios N
Published: April 2021

ABSTRACT

PURPOSE: To study transition zone excimer laser photorefractive keratectomy (PRK) in moderate and high myopia defined as a spherical equivalent of -7.00 diopters (D) or more. The follow-up period was 18 months.

METHODS: Forty eyes of 40 patients with myopia of 7.00 to - 13.50 D (mean ± SD, -921 ± 1.98) underwent transition zone (5.0 to 7.0 mm transition zone) PRK using the Aesculap Meditec Mel 60 excimer laser. The mean attempted correction was 8.3 ± 1.64 D (range: -6.50 to -12.00 D).

RESULTS: At 18 months, 83% achieved an unaided visual acuity of 20/50 or better and HOW 12% 20/25 or better. Eighty-eight percent were within ±2 D of emmetropia. The mean spherical equivalent was -1.1 D (+3.00 to -9.00 D).

CONCLUSIONS: Transition zone PRK is useful in moderate to high myopia. Regression, as well as overcorrection are issues for further investigation. [J Refract Surg. 1996;12:S261-S263.]
Disability Glare After Excimer Laser Photorefractive Keratectomy for Myopia
Authors: Niesen Ulrike M , Businger Urs , Schipper Isaak
Published: April 2021

ABSTRACT

BACKGROUND: A change of corneal topography and haze after excimer laser photorefractive keratectomy (PRK) can reduce contrast sensitivity and cause glare. Both glare and contrast sensitivity can be examined in a reproducible manner with one instrument.

METHODS: We have used the Berkeley Glare Test to examine 46 eyes of 32 patients before and 1, 3, 6, 9, and 12 months after excimer laser PRK for moderate to high myopia. Multiple regression analysis was used for statistical analysis.

RESULTS: High contrast visual acuity showed a statistically significant deterioration during the first 6 months after PRK (p=0.01); 1 year after treatment visual acuity returned to almost pretreatment levels (p=0.2). High- and low contrast visual acuity under glare deteriorated significantly 3 months after PRK and had only risen slightly 1 year later (p≤0.0065). A similar development could be observed for the low contrast visual acuity without glare.

CONCLUSION: Although high contrast visual acuity recovers by 1 year after PRK, low contrast visual acuity and glare deteriorate significantly and do not recover, even after 1 year. [J Refract Surg. 1996;12:S267-S268.]
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]
Long-term Effects of Radial Keratotomy on the Corneal Endothelium
Authors: MacRae Scott M , Rich Larry F
Published: April 2021

ABSTRACT

BACKGROUND: The long-term effects of radial keratotomy on the corneal endothelium are not well understood. We evaluated the effects of radial keratotomy on the corneal endothelium on the central and midperipheral corneal endothelium.

METHODS: Anterior radial keratotomy in 25 eyes was performed and patients were followed for a duration of 4 to 10 years after surgery. Eleven non- contact lens wearing control eyes did not have surgery and were followed for the same period. Morphometric analysis of specular microscopic images was performed with regard to cell density, percent hexagonality, and coefficient of variation.

RESULTS: Mean corneal endothelial cell loss rates were 0.4% per year in the radial keratotomy group and 0.9% in the untreated control group over the study duration (mean 7 yr). Morphometric analysis of the cells failed to show a significant change in hexagonality and coefficient of variation. Evaluation of the midperipheral corneal cell counts demonstrated a 1% per year cell loss rate. The cell loss rates in radial keratotomy patients followed over this period were consistent with that noted for normal aging (0.5 to 2.5% per year).

CONCLUSION: Radial keratotomy does not cause accelerated endothelial cell loss over 4 to 10 years. [J Refract Surg 1998;14:49-52]
Therapeutic Alloplastic Laser in situ Keratomileusis for Myopia
Authors: Maldonado-Bas Arturo , Pulido-Garcia Ruben
Published: April 2021

ABSTRACT

BACKGROUND: A new technique, therapeutic alloplastic laser in situ keratomileusis to correct high myopia, is introduced.

METHODS: Therapeutic alloplastic laser in situ keratomileusis consists of neutral homoplastic epikeratoplasty combined with superficial keratectomy performed with an excimer laser and/or a microkeratome. Indications for the technique are: myopia over 20 diopters (D), eyes with corneal scarring after photorefractive keratectomy (PRK), complications following keratomileusis, radial keratotomy complications with undercorrection, and keratoconus suspect myopic eyes.

RESULTS: In all five eyes we achieved precise corneal lathing with the microkeratome or the excimer laser, and obtained a clear allograft. In all eyes, we maintained or improved the patient's spectacle-corrected visual acuity related to baseline values. We did not induce astigmatism, and corneal thickness was almost unchanged.

CONCLUSIONS: Advantages of therapeutic alloplastic laser in situ keratomileusis are that it provides a Bowman's layer for the cornea following keratectomy, it is possible to lathe ablation diameters larger than 5 mm, it prevents the appearance of corneal haze, and reduces the need for corticosteroid treatment. [J Refract Surg 1998;14:64-69]