Refractive Keratotomy Research Articles

Refractive results of cataract surgery using optical biometry and Haigis formula in eyes with refractive keratotomy

OBJETIVO: Analisar os resultados refracionais no pós-operatório de cirurgia de catarata em olhos previamente submetidos à ceratotomia, utilizando a fórmula Haigis e os dados fornecidos pelo biômetro óptico IOL Master®. MÉTODOS: As medidas para o cálculo da LIO foram obtidas por meio da biometria óptica por interferometria de coerência parcial (IOL Master® – Zeiss, versão 5.4 e 5.5) que nos fornece o comprimento axial, a ceratometria central de 2.5mm, o diâmetro branco-a-branco e a profundidade anatômica da câmara anterior. A [...]

Deep anterior lamellar keratoplasty for the management of iatrogenic keratectasia occurring after hexagonal keratotomy

Iatrogenic keratectasia has been reported subsequent to refractive surgery or trauma. Hexagonal keratotomy (HK) is a surgical incisional technique to correct hyperopia. A number of complications have been reported following this procedure, including irregular astigmatism, wound healing abnormalities and corneal ectasia. When visual acuity is poor because of ectasia or irregular astigmatism and contact lens fitting is not possible, penetrating or lamellar keratoplasty can be performed. Since incisions in refractive keratotomy are set at 90–95% depth of cornea, intraoperative microperforations are known to occur and lamellar keratoplasty may become difficult. We describe deep anterior lamellar keratoplasty (DALK) used to successfully manage keratectasia after HK. Pre DALK vision was 20/400 and post DALK vision was 20/30 two months after surgery. This report aims to show improved visual outcome in corneal ectasia secondary to HK. DALK can be a procedure of choice with proper case selection.

Corneal Wound Healing After Keratorefractive Procedures

Research into corneal wound healing is gaining renewed interest with the increasing volume of keratorefractive procedures. Such research may help avoid the complication of ectasia after laser refractive surgery. There are three histopathological types of wound healing after keratorefractive surgery – whether laser refractive surgery, penetrating keratoplasty or radial keratotomy – and these are reviewed in this paper. They are hypercellular fibrotic stromal scar preceded by activated keratocytes, epithelial hyperplasia or hypertrophy and hypocellular primitive stromal scar. All can be identified with light, electron and immunofluorescence microscopy (or, with less detail, by confocal microscopy). A single procedure can manifest all three types of wound healing. Tissue destruction is part of tissue remodelling, but in successful procedures destruction cannot be uncontrolled or excessive. The elucidation of the signalling components remains an important area of research.

Cataract and Refractive Surgery

Thomas Conen and Douglas D. Koch (eds) Cataract and Refractive Surgery In: G. K. Krügelstain and R. N. Weinreb (eds) Essentials in Ophthalmology 324 pages Springer Verlag, Berlin, Heidelberg, New York, 2005 ISBN 3 540 20046 0 Price: $99.00 Essentials in Ophthalmology is a review series covering eight different topics in ophthalmology, of which cataract and refractive surgery represents one. A new book of review in each area will be published every 2 years. This particular volume contains 10 chapters on cataract and nine on refractive surgery. Obviously not all aspects of these two quickly developing areas in ophthalmic surgery can be covered in this first volume. Each chapter, however, is designed in a didactic manner and begins with core messages, where the take-home information can be digested in 20 seconds. Each section within a chapter is also summarized in between three and five sentences, in what is called a ‘summary for clinicians’. This enables the reader to acquire an abstract view of each chapter very quickly and without reading the details. The authors are all well known surgeons and scientists working within the international arena and, although they stick to the same format, each of them frequently adds his or her personal touch to their own particular chapters, for better or for worse. As we all know, illustrations, particularly colour photographs, are difficult to obtain in the field of ophthalmology and in this book the illustrations range from the excellent to the not-so-good. This volume paints the cataract and refractive scene of 2002–03. This means that if you want to read about today's hot topics, such as Epilasik, you will have to wait for the next volume. For those who want to acquire an update of modern cataract and refractive surgery, this is an effective and enjoyable way to do so. Three chapters, in particular, recommend this book. The first is the chapter on accommodative intraocular lenses by Oliver Findel. This must be the best description of a complex and controversial subject published so far. Further, the chapter by Rupert Menapase on the prevention of posterior capsule opacification should become required textbook reading in the future. For those of us who enjoy a bit of an historical perspective and a touch of when, who, why and why not, the chapter on refractive keratotomy ‘Does it have a future role in refractive surgery?’ is not only very educational, but is a true pleasure to read. As an added bonus for cataract surgeons interested in surgical techniques, another chapter clearly delineates the difference between ‘chip and flip’, ‘crack and flip’, ‘fako chop’, ‘chew chew chop and flip’ and a few other variations on this theme. Given the rapid development in these two fields of ophthalmic surgery, I look forward with anticipation to the next volume in this series. It will, I am sure, include chapters on today's hot topics, such as patient benefit from ophthalmic surgery and newly evident complications that are inherent in every surgical technique in the areas of both cataract and refractive surgery.

Toric intraocular lenses for correcting astigmatism in 130 eyes

Myopia, hyperopia, and presbyopia are now fully correctable, with judicious selection of the IOL. Astigmatism, the irregular curvature of the corneal surface, remains, however, the single most common reason that patients require spectacle correction after cataract surgery. Large incision cataract surgery induced a large degree of postoperative astigmatism; today’s small, clear corneal cataract incision can create astigmatic neutrality. These same small incisions can also be fashioned to correct preexisting astigmatism at the time of cataract surgery. The surgical correction of astigmatism with corneal relaxing incisions, such as the arcuate kertotomy technique of Thornton, 1 Thornton S.P. Radial and Astigmatic Keratotomy. Slack, Thorofare, NJ1994 Google Scholar the keratolenticuloplasty technique that I have advanced, 2 Kershner R.M. Refractive Keratotomy for Cataract Surgery and Correction of Astigmatism. Slack, Thorofare, NJ1994 Google Scholar , 3 Kershner R.M. Keratolenticuloplasty arcuate keratotomy for cataract surgery and astigmatism. J Cataract Refract Surg. 1995; 21: 274-277 Abstract Full Text PDF PubMed Scopus (29) Google Scholar , 4 Kershner R.M. Clear corneal cataract surgery and the correction of myopia, hyperopia and astigmatism. Ophthalmology. 1997; 104: 381-389 Abstract Full Text PDF PubMed Scopus (43) Google Scholar , 5 Kershner R.M. Refractive cataract surgery. Curr Opin Ophthalmol. 1998; 9: 46-54 Crossref PubMed Scopus (14) Google Scholar and the limbal relaxing incision of Gills 6 Gills J.P. Optimizing vision with limbal relaxing incisions. Ophthalmol Management Oct. 1997; 1: 2 Google Scholar have all been recently popularized. Each has ability to alter corneal topography, flattening the steep corneal meridian and neutralizing preexisting astigmatism. Unfortunately, because of the technical and surgical skill involved, the need for diamond keratomes, and additional surgical instrumentation, many surgeons have not fully availed themselves of the advantages of astigmatic correction afforded by refractive keratotomy.

Current Trends in Cataract and Refractive Surgery in Japan: 1998 Survey

Purpose: A seventh annual survey was carried out by mail in February 1999 to investigate the current trends in cataract and refractive surgery in Japan. Methods: Questionnaires were sent to 925 ophthalmologist members of the Japanese Society of Cataract and Refractive Surgery. Data received from 411 (44.4%) of the recipients were cross-analyzed and compared with those from the previous surveys. Results: In cataract surgery, 93% of respondents preferred phacoemulsification, 58% employed the self-sealing wound closure technique, and 23% used topical anesthesia for phacoemulsification. Conclusions: There have been trends toward more surgical procedures performed by a surgeon, shorter period of hospitalization, and increased number of outpatient procedures. In refractive surgery, surgeons remained rather conservative; with 26% and 5% of surgeons doing astigmatic keratotomy and refractive keratotomy, respectively. Photorefractive keratectotomy, laser in situ keratomileusis, phakic intraocular lens, and intrastromal corneal ring were judged to be useful refractive surgical procedures by 58.2%, 69.5%, 25.4%, and 8.8% of the respondents, respectively.

Early- versus late-onset infectious keratitis after radial and astigmatic keratotomy: Clinical spectrum in a referral practice

Purpose To compare the clinical characteristics of early- versus late-onset keratitis after radial keratotomy (RK) and astigmatic keratotomy (AK). Setting Referral subspecialty practice. Methods This retrospective review comprised 19 patients with infectious keratitis after RK and AK. Early- versus late-onset groups were analyzed for predisposing conditions; infiltrate location, size, and depth; microbiologic data; and final visual outcome. Results Ten patients in the early-onset group developed keratitis within a mean of 7.4 days after surgery (range 3 to 14 days). Nine patients in the late-onset group developed keratitis a mean of 5.4 years after surgery (range 1.5 to 15.0 years). Staphylococcus aureus was the predominant organism in the early-onset group and Pseudomonas aeruginosa in the late-onset group. In the early-onset group, most infiltrates occurred in the paracentral aspect of the RK incision and extended to the middle or posterior stroma. In the late-onset group, most infiltrates occurred in the peripheral portion of the RK incision and were localized to the superficial stroma. A hypopyon was present in 7 of 10 ulcers in the early group and in 1 of 9 in the late group. Two patients in the early group developed endophthalmitis. Most patients in the late-onset group had incisional pseudocysts; 2 had other risk factors for keratitis. Final visual acuity was 20/40 or better in 7 of 10 patients in the early group and in 8 of 9 patients in the late group. Conclusions Early-onset corneal ulcers after incisional refractive keratotomy were usually paracentral and deep, whereas late-onset ulcers were usually peripheral and superficial. Despite the predominance of Staphylococcus and Pseudomonas in the early- and late-onset groups, respectively, a variety of organisms may be responsible for infections in keratotomy incisions.

Current Trends in Cataract and Refractive Surgery in Japan: 1997 Survey

Purpose: A sixth annual survey was carried out by mail in January 1998, to investigate the current trends in cataract and refractive surgery in Japan. Respondents: Questionnaires were sent to 816 ophthalmologist members of the Japanese Society of Cataract and Refractive Surgery. Data received from 409 (50.1%) of the recipients were cross-analyzed and compared with those from the previous surveys. Results and Conclusion: In cataract surgery, there have been trends toward more surgical procedures performed by a surgeon, shorter period of hospitalization, and increased number of outpatient surgery. Ninety-two percent of respondents preferred phacoemulsification, 54% used the self-sealing wound-closure technique, and 19% used topical anesthesia for phacoemulsification. As for refractive surgery, surgeons remained rather conservative; with 28% and 7% of surgeons doing astigmatic keratotomy and refractive keratotomy, respectively. Photorefractive keratectomy, laser in situ keratomileusis, and phakic intraocular lens were judged to be useful refractive surgical procedures by 56.6%, 43.3%, and 25.1% of the respondents, respectively.

Laser in situ keratomileusis for undercorrection after radial keratotomy.

To assess the safety and efficacy of excimer laser in situ keratomileusis (LASIK) in treating residual myopia and/or astigmatism following refractive keratotomy. Fourteen eyes that had previously undergone radial and/or arcuate keratotomy were included. The surgeries were performed using the Chiron Automated Microkeratome and the VISX 20/20B excimer laser. Average follow-up was 12.64+/-5.02 months. Mean spherical equivalent refraction was reduced from -3.48+/-3.52 D preoperatively to -0.04+/-0.87 D postoperatively. At the last follow-up examination there were 8 eyes (57.1%) with a refraction within+/-0.50 D, and 10 eyes (71.4%) within +/-1.00 D of emmetropia. Uncorrected visual acuity was 20/20 or better in 4 eyes (28.6%) and 20/40 or better in 10 eyes (71.4%). Vector analysis of the astigmatic correction showed an index of success of 80%. There was no significant loss (> or = or =2 lines) of spectacle-corrected visual acuity. We observed interface epithelial ingrowth in one eye. The correction of residual myopia and/or astigmatism with LASIK in eyes with prior refractive keratotomy proved to be safe and effective. Careful preoperative evaluation may help to avoid complications such as reopening of incisions during surgery or postoperative ingrowth of epithelium beneath the corneal flap.

Current Trends in Cataract and Refractive Surgery in Japan: 1996 Survey

A fifth annual survey was carried out by mail in February 1997 to investigate the current trends in cataract and refractive surgery in Japan. A questionnaire was sent to 867 ophthalmologist members of the Japanese Society of Cataract and Refractive Surgery. Data received from 440 (50.7%) of the recipients were cross-analyzed and compared with those from the previous surveys. For cataract surgery, there have been trends toward more surgical procedures performed by a surgeon, shorter period of hospitalization, and increased number of outpatient surgery. Ninety percent of respondents preferred phacoemulsification, 42% employed the self-sealing wound closure technique, and 26% used topical anesthesia for phacoemulsification. As for refractive surgery, surgeons remained rather conservative, with 26% and 6% of surgeons doing astigmatic keratotomy and refractive keratotomy, respectively.

Unilateral refractive keratotomy for anisometropia.

In anisometropia, the asymmetry of refractive error produces disparity of image magnification (aniseikonia) that can create visual discomfort, especially when asymmetry is 3.00 diopters or more. A prospective study of 20 eyes of 20 patients between 18 and 61 years of age who underwent unilateral radial and/or transverse keratotomy was conducted; results of at least 12 months follow-up are presented. The efficacy of keratotomy was evaluated by the following criteria: 1) change in spherical and cylindrical refraction, 2) decrease in refraction difference between two eyes of each patient, 3) change in spectacle-corrected visual acuity, and 4) change in binocular vision functions and asthenopic complaints. Mean decrease in spherical refractive error was 3.66 +/- 1.58 D (range, 1.25 to 7.50 D) and 2.08 +/- 0.81 D (range, 1.00 to 3.50 D) in astigmatic refraction. The mean refraction difference between two eyes was 4.90 +/- 2.20 D preoperatively, and this difference regressed to 1.79 +/- 1.42 D postoperatively. Spectacle-corrected visual acuity increased in seven eyes (35%), remained the same in 12 eyes (60%) and decreased in one eye (5%). All patients reported relief of asthenopic complaints. Fusion amplitudes increased in 12 (60%) patients. Stereoscopic vision improved in five (25%) patients. Monocular refractive keratotomy can significantly decrease anisometropia.

Two-incision radial keratotomy for low myopia with astigmatism

Purpose: To evaluate the effectiveness of two-incision radial keratotomy (RK) in correcting low-magnitude refractive myopic astigmatism.Setting: Two clinical study sites, one in St. Louis, Missouri, USA, the other in Caracas, Venezuela.Methods: Fifty-seven eyes of 43 patients with low-magnitude myopic astigmatism had two-incision RK at one of two clinical study sites. In the initial phase of this series, 10 eyes with amblyopia at the 20/30 level had surgery at one center. Refractive keratotomy was performed with the radial incision placed in the plus cylinder axis of refraction. This axis was verified as the meridian of greatest corneal curvature by standard keratometry and computer-assisted corneal topographic analysis. Two eyes received a second operation (enhancement).Results: Mean follow-up was 11.1 months (range 6 to 12 months). Mean preoperative and postoperative myopic spherical equivalent measured -1.42 diopters (D) ± 0.51 (SD) and -0.14 ± 0.39 D, respectively; the mean reduction was 1.28 ± 0.59 D (P = .0001). Mean preoperative and postoperative refractive astigmatism was 1.41 ± 0.45 D and 0.48 ± 0.33 D, respectively (P = .0001). Mean preoperative and postoperative keratometric astigmatism was 1.26 ± 0.54 D and 0.31 ± 0.35 D, respectively, a mean reduction of 0.95 D (P = .0001). The surgical meridian was flattened by an average of 2.06 D by keratometry and the orthogonal meridian, by an average of 1.10 D. Preoperative uncorrected visual acuity (UCVA) was 20/40 or better in five (9%) eyes (range counting fingers to 20/40). Postoperative UCVA acuity was 20/40 or better in all eyes (mean acuity 20/25). In the nonamblyopic subgroup, mean postoperative UCVA was 20/24.Conclusions: A limited number of radial incisions placed in the topographically confirmed axis of greatest curvature are effective in the treatment of low-magnitude myopic astigmatism.

Casebeer System for refractive keratotomy: Patient satisfaction

Purpose: To evaluate patient satisfaction 3 years after radial keratotomy (RK) using the Casebeer nomograms.Setting: The Werblin Center, Princeton, West Virginia.Methods: This study assessed the satisfaction of 96 patients who had bilateral distance correction by RK using the Casebeer System. The cases were part of the first 241 consecutive refractive keratotomy procedures (N = 128 patients) performed by one surgeon. Ninety-nine percent of the 96 patients in this study completed a questionnaire on satisfaction and visual symptoms 3 years postoperatively. A separate control population of 105 consecutive patients about to have RK surgery were asked to complete a questionnaire about their preoperative symptoms.Results: Ninety-eight percent of patients were very to moderately satisfied 3 years after the procedure, 99% said they would have surgery again if given the chance, and 96% said they would recommend it to others. However, 69% stated they had mild to very severe symptoms 3 years postoperatively compared with 28% in the control group.Conclusion: Despite an extremely high degree of patient satisfaction, about 99%, the 1 % dissatisfaction rate seen in this study could be very significant in this young, potentially litigious patient population.

Three year results of refractive keratotomy using the Casebeer System

Purpose: To analyze the results of one surgeon's first refractive keratotomy surgeries. Setting. The Werblin Center, Princeton, West Virginia.Methods: The three year results of 241 consecutive surgical procedures (128 patients) using Casebeer nomograms were examined. The average preoperative myopia was −4.07 ± 1.89 diopters (D). Two hundred twenty-two eyes were corrected with a goal of emmetropia. Two hundred of 241 eyes (83%) were followed for 3 years; 35 eyes (15%) were followed for fewer than 3 years after the last enhancement procedure, and 6 eyes (2%) were lost to follow-up.Results: At 3 years postoperatively (range 30 to 44 months), excluding postoperative suture and ALK procedures, mean residual manifest refractive error (spherical equivalent) was −0.04 ± 0.67 D (−2.25 to +3.13 D). Mean residual cycloplegic error was +0.45 ± 0.76 D (−1.00 to +4.13 D). Eighty-seven eyes (36%) required between one and six enhancement procedures. One hundred fifteen eyes (52%) had 20/20 or better visual acuity and 214 eyes (96%), 20/40 or better. One hundred fifty-two eyes (84%) were within ±1.0 D and 120 eyes (66%) were within ±0.5 D. Ten eyes (4%) lost one or more lines of best corrected acuity.Conclusion: Using the Casebeer system for refractive keratotomy, we obtained 20/40 or better uncorrected visual acuity in 96% of eyes with low to moderate levels of myopia. However, a significant number of enhancement procedures, 36% overall, were required to achieve this level of success. Hyperopic shift remains a significant concern following radial keratotomy procedures.

Hyperopic shift after refractive keratotomy using the Casebeer System

Purpose: To determine the degree of hyperopic shift following refractive keratotomy.Setting: The Werblin Center, Princeton, West Virginia.Methods: The results of 241 consecutive radial/astigmatic keratotomy procedures in 128 patients were studied. All procedures were performed using Casebeer nomograms. Refractive follow-up information was obtained for 78% of patients at 3 months (range 1 to 6 months), 1 year (range 6 to 21 months), and 3 years (range 30 to 44 months).Results: Overall, the amount of hyperopic change decreased significantly (P < .05) during the 3 year period, from +0.34 diopters (D) per year to +0.12 D per year. Eyes with more than 6.0 D of preoperative intended correction were more unstable (+0.49 D in the first year and +0.44 D in the second and third years) than eyes with less than 5.0 D (+0.27 D and +0.05, respectively).Conclusion: Because the average magnitude of the hyperopic shift was +0.6 D in the first 3 years after surgery, a slight undercorrection, -0.5 D to -0.7 D, should be the refractive endpoint for primary and enhanced refractive keratotomy surgery.

One-year Results of a Prospective Multicenter Study of the Casebeer System of Refractive Keratotomy

To evaluate the clinical results, predictability, stability, safety, and the patient satisfaction after refractive keratotomy for the correction of myopia and astigmatism using a defined protocol (the Casebeer system). The authors enrolled 324 patients (615 eyes) in a prospective study conducted by 18 surgeons. All procedures were performed using ultrasonic pachymetry with the diamond knife blade set at a length of 100% of the temporal paracentral corneal thickness reading and four to eight centripental (Russian style) incisions with or without fixation of the globe. Straight transverse incisions were done for astigmatism in 222 (36%) eyes. One to eight repeated operations (enhancements) were done on 241 (39%) eyes. Mean baseline cycloplegic refraction was -3.68 +/- 1.59 diopters (D) (range, -0.88 to -8.25 D). One-year data were available for 546 eyes (89%). At 1 year, mean spherical equivalent cycloplegic refraction was -0.27 +/- 0.78 D (range, -3.13 to +3.00 D). There were 373 (68%) eyes with a refraction of +/- 0.50 D, and 483 eyes (89%) within +/- 1.00 D of emmetropia. Ten eyes (2%) were overcorrected by more than 1.00 D. Mean baseline refractive cylinder was 1.01 +/- 0.75 D (range, 0-5.75 D); at 1 year, the mean cylinder was 0.40 +/- 0.55 D (range, 0-2.50 D). Uncorrected visual acuity was 20/20 or better in 297 (54%) eyes and 20/40 or better in 93%. Six eyes (1%) lost two to three lines of spectacle-corrected visual acuity; the worst visual acuity was 20/30. Of patients responding to a standardized questionnaire, 320 (77%) wore no spectacles for distance or near vision; there was a significant increase in glare and fluctuation of vision from baseline; and 247 (90%) were very satisfied with the outcome. Refractive keratotomy using radial incisions with or without transverse incisions and following the Casebeer system effectively reduces and often eliminates myopia and astigmatism with a high degree of safety. Enhancement surgery was required in 39% of eyes. Glare and fluctuation of vision increased postoperatively but were rated mild, and patient satisfaction was high.

Intraocular lens power calculation for eyes after refractive keratotomy

BACKGROUND Calculating the intraocular lens (IOL) power for an eye that has previously had refractive keratotomy is a problem because of the difficulty of accurately measuring the central power of the cornea using standard keratometers. METHODS Three methods are proposed to better estimate this parameter. The clinical history method involves subtracting the change in myopia induced by the refractive keratotomy from the average corneal power measured before the keratotomy. The contact lens method determines the difference between the manifest refraction with and without a plano hard contact lens of known base curve and subtracts this difference from that base curve. Videokeratography measures the central corneal power inside the approximately 3-mm zone measured by keratometry, and therefore gives a more accurate power to use in IOL calculation formulas, especially with newer software applications becoming available. RESULTS Published reports have demonstrated that standard keratometers do not accurately measure corneal power after refractive keratotomy and that regression formulas are less accurate than modern third-generation theoretic formulas for eyes that have flatter corneas from refractive surgery. CONCLUSION For eyes that have had refractive surgery, the corneal power derived from clinical history, contact lens refraction, or videokeratography should be used in a third-generation theoretic formula (Hoffer Q, Holladay, SRK/T) to calculate the intraocular lens power used during cataract surgery.

Eye infections after refractive keratotomy.

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. 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. 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%). 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.

Photorefractive keratectomy following radial keratotomy.

Excimer laser photorefractive keratectomy (PRK) has been used to correct residual myopia in eyes that have had refractive keratotomy. Nine eyes of eight patients were studied at a mean of 13 months after PRK. Previous procedures included radial keratotomy (9 eyes) and myopic keratomileusis (1 eye). PRK was performed using a Summit Technology excimer laser with a 5.0-mm diameter ablation zone. Uncorrected visual acuity improved in 7 of 9 eyes. The refractive outcome was within 1.00 diopter (D) of attempted correction for 3 of 9 eyes. Spectacle-corrected visual acuity decreased 2 or more Snellen lines in 2 of 9 eyes. Subepithelial corneal stromal haze was seen 1 month postoperatively in 6 of 8 eyes and was present in 4 of 6 eyes at 1 year. Stromal haze was associated with regression of the refractive effect of the PRK. PRK in eyes with previous radial keratotomy appears to be less predictable and may be associated with greater corneal haze and regression of refractive correction than in previously unoperated eyes. Activation of stromal fibroblasts in the previous corneal incisions may cause these findings.

Intraocular lens power calculation for eyes after refractive keratotomy.

Calculating the intraocular lens (IOL) power for an eye that has previously had refractive keratotomy is a problem because of the difficulty of accurately measuring the central power of the cornea using standard keratometers. Three methods are proposed to better estimate this parameter. The clinical history method involves subtracting the change in myopia induced by the refractive keratotomy from the average corneal power measured before the keratotomy. The contact lens method determines the difference between the manifest refraction with and without a plano hard contact lens of known base curve and subtracts this difference from that base curve. Videokeratography measures the central corneal power inside the approximately 3-mm zone measured by keratometry, and therefore gives a more accurate power to use in IOL calculation formulas, especially with newer software applications becoming available. Published reports have demonstrated that standard keratometers do not accurately measure corneal power after refractive keratotomy and that regression formulas are less accurate than modern third-generation theoretic formulas for eyes that have flatter corneas from refractive surgery. For eyes that have had refractive surgery, the corneal power derived from clinical history, contact lens refraction, or videokeratography should be used in a third-generation theoretic formula (Hoffer Q, Holladay, SRK/T) to calculate the intraocular lens power used during cataract surgery.