Excimer Laser Photorefractive Keratectomy For Myopia Research Articles

Long-Term Prospective Follow-Up Study of Myopic Photorefractive Keratectomy

The aim of this study was to evaluate the long-term outcome of excimer laser myopic photorefractive keratectomy (PRK). We undertook an 11-year prospective follow-up study of visual and refractive outcomes in 46 patients (85 eyes). The main outcome measures were predictability, efficacy, stability and safety of PRK. At 11 years after the operation, 56.5% of eyes were within ±0.5 D of attempted correction and 81.2% were within ±1.0 D; 87% had vision of 20/40 or better, and 52% had 20/20 or better. The best spectacle-corrected visual acuity was unchanged or improved in 91% of eyes at 11 years. Eyes with moderate and severe myopia showed a significant change between 3 and 11 years. PRK surgery for myopia shows predictable and stable results in the long term, with a slight regression in refraction, mainly for patients with severe myopia.

EXCIMER LASER

Objectives: To evaluate the efficacy and safety of excimer laserphotorefractive keratectomy for myopia in Pakistani people. Design: Prospective study. Setting: At Al-Shifa Trust EyeHospital Rawalpindi. Period: October, 1995 and Febrauray, 1996. Material & Methods: The study group of thirteenpatients, comprises of 25 eyes, with refractive error ranging from -1.50 to -3.50 D.S (diopters sphere) and less than-1.50 D.C (diopters cylinder).Results: Thirteen eyes (52%) lost to follow up after three months. Only twelve eyes (48%)could be reviewed at six months after photorefractive keratectomy. At one month, eleven eyes (44%) and at threemonths, eight eyes (32%) were hypermetropic within +0.25 to +1.00 diopters of spherical equivalent .At six months onlythree eyes (25%) had hypermetropia within +0.25 to +1.00 diopters spherical equivalent. None of the eyes had anykind of astigmatism more than 1.00 diopter. No over correction of more than +1.00 diopter of spherical equivalent wasobserved in any case. At one month, three months and six months after photo-refractive keratectomy, 88%, 80% and100% eyes had 6/6 visual acuity respectively, without any optical aid. Hundred percent of the eyes showed completehealing of the epithelium on third post operative day. Moderate to severe postoperative pain was experienced by everyone for three days with gradual reduction in intensity. Only one eye (8.33%) had grade 1 haze at six months. Restsof the eyes were clear .No vision threatening complications occurred. Despite the short term follow up, photorefractivekeratectomy appears to be an effective and safe procedure with good predictability for the correction of low myopia.Conclusion: Despite relatively short term follow up of the study; photo refractive keratectomy (PRK) appears to be safeand quite predictable procedure for correction of low myopia.

Ten-year Follow-up of Photorefractive Keratectomy for Myopia of Less Than −6 Diopters

To evaluate the long-term outcomes of excimer laser myopic photorefractive keratectomy (PRK) for myopia of less than -6 diopters (D). Long-term (10-year) follow-up retrospective, interventional case series. The study included 225 eyes of 138 myopic patients with spherical equivalent (SE) between 0 and -6 D treated with myopic PRK at the Instituto Oftalmológico de Alicante, Alicante, Spain, using the VISX 20/20 excimer laser (Santa Clara, California, USA). The main outcome measures were refractive predictability and stability, mean corneal keratometry, topographical cylinder, safety, efficacy, stability of visual acuity, and postoperative complications. At 10 years, 169 (75%) of 225 eyes were within +/- 1.00 D and 207 (92%) were within +/- 2.00 D. Ninety-five (42%) eyes underwent retreatments because of overcorrection, regression, or both. The mean SE slightly decreased (myopic regression) with a mean magnitude of -0.10 +/- 1.08 D over 10 years (-0.01 +/- 0.11 D per year). Forty-one (58%) of 225 eyes demonstrated increase in best spectacle-corrected visual acuity after 10 years. Only one eye lost eight lines because of significant cataract, and two eyes lost vision (one lost seven lines and the other lost four lines) because of posterior segment-related complications. The mean corneal haze score gradually decreased from 0.22 +/- 0.39 at three months to 0.01 +/- 0.09 at 10 years. Photorefractive keratectomy for myopia of less than -6 D is a safe and effective procedure in the long-term.

Ten-Year Follow-up of Photorefractive Keratectomy for Myopia of More Than −6 Diopters

To evaluate the long-term outcomes of excimer laser myopic photorefractive keratectomy (PRK) for myopia higher than -6 diopters (D). A long-term (10-year) follow-up retrospective, interventional case series. The study included 267 eyes of 191 patients with myopia with spherical equivalent (SE) of more than -6 D treated with myopic PRK at the Instituto Oftalmológico de Alicante, Alicante, Spain, using the VISX 20/20 excimer laser (Santa Clara, California, USA). All patients were evaluated three months, one year, two years, five years, and 10 years after surgery. The main outcome measures were refractive predictability and stability, mean corneal keratometry, topographical cylinder, safety, efficacy, stability of visual acuity, and postoperative complications. At 10 years, 156 (58%) of 267 eyes were within +/- 1.00 D and 209 (78%) were within +/- 2.00 D. One hundred and twenty-four eyes (46.4%) underwent retreatments because of overcorrection, regression, or both. The mean SE decreased (myopic regression) in eyes that did not undergo retreatment, with a mean magnitude of -1.33 +/- 2.0 D over 10 years (-1.13 +/- 0.20 D per year). One hundred and twenty-one (48.3%) of 267 eyes demonstrated increase in best spectacle-corrected visual acuity, and only eight eyes lost lines of vision because of cataract and posterior segment-related complications. The mean corneal haze score decreased gradually from 0.48 +/- 0.69 at three months to 0.09 +/- 0.33 at 10 years. PRK for myopia of more than -6 D is a safe and effective procedure in the long-term.

Error in Author Name in: The Corneal Endothelium After Myopic Excimer Laser Photorefractive Keratectomy

Error in Author Name. In the article titled “The Corneal Endothelium After Myopic Excimer Laser Photorefractive Keratectomy,” published in the November 1995 issue of the ARCHIVES (1995;113:1356), the second author's name should have appeared as follows: M. C. Hernaez-Ortega, MD, PhD.

A long-term study of photorefractive keratectomy*112-year follow-up

Objective To evaluate long-term refractive stability of excimer laser myopic photorefractive keratectomy (PRK). Design A long-term (12 years) prospective follow-up study. Participants Sixty-eight patients (56.6%) of the original cohort of 120 who participated in the first United Kingdom excimer laser clinical trial underwent detailed clinical assessment at 12 years after myopic PRK. Intervention Myopic PRK was performed using the Summit Technology UV 200 excimer laser with a 4-mm ablation zone. Patients were allocated to 1 of 6 treatment groups based on their preoperative refraction. Each group received one of the following spherical corrections: −2, −3, −4, −5, −6, or −7 diopters (D). Patients in each group received an identical treatment, and therefore, emmetropia was not the primary aim. Main outcome measures Refractive stability, refractive predictability, best spectacle-corrected visual acuity (BSCVA), and corneal haze. Results The postoperative refraction remained stable at 12 years, with no significant change in mean spherical equivalent refraction between 1, 6, and 12 years. Seventy-five percent of patients who underwent a −2-D correction and 65% of patients who received a −3-D correction were within 1 D of intended correction at 12 years. Fifty-seven percent of the −4-D group and 50% of the −5-D group were within 1 D, and this was further reduced to 25% and 22% in the −6-D and −7-D groups, respectively. Four percent had residual corneal haze, and 12% had persistent nighttime halos at 12 years. Dry eyes were encountered in 3% of patients, and none of the eyes developed corneal ectasia in the long term. Conclusions In myopic PRK, refractive stability achieved at 1 year was maintained up to 12 years with no evidence of hyperopic shift, diurnal fluctuation, or late regression in the long term. Corneal haze decreased with time, with complete recovery of BSCVA. Night halos remained a significant problem in a subset of patients due to the small ablation zone size.

A long-term study of photorefractive keratectomy: 12-year follow-up

Objective To evaluate long-term refractive stability of excimer laser myopic photorefractive keratectomy (PRK). Design A long-term (12 years) prospective follow-up study. Participants Sixty-eight patients (56.6%) of the original cohort of 120 who participated in the first United Kingdom excimer laser clinical trial underwent detailed clinical assessment at 12 years after myopic PRK. Intervention Myopic PRK was performed using the Summit Technology UV 200 excimer laser with a 4-mm ablation zone. Patients were allocated to 1 of 6 treatment groups based on their preoperative refraction. Each group received one of the following spherical corrections: −2, −3, −4, −5, −6, or −7 diopters (D). Patients in each group received an identical treatment, and therefore, emmetropia was not the primary aim. Main outcome measures Refractive stability, refractive predictability, best spectacle-corrected visual acuity (BSCVA), and corneal haze. Results The postoperative refraction remained stable at 12 years, with no significant change in mean spherical equivalent refraction between 1, 6, and 12 years. Seventy-five percent of patients who underwent a −2-D correction and 65% of patients who received a −3-D correction were within 1 D of intended correction at 12 years. Fifty-seven percent of the −4-D group and 50% of the −5-D group were within 1 D, and this was further reduced to 25% and 22% in the −6-D and −7-D groups, respectively. Four percent had residual corneal haze, and 12% had persistent nighttime halos at 12 years. Dry eyes were encountered in 3% of patients, and none of the eyes developed corneal ectasia in the long term. Conclusions In myopic PRK, refractive stability achieved at 1 year was maintained up to 12 years with no evidence of hyperopic shift, diurnal fluctuation, or late regression in the long term. Corneal haze decreased with time, with complete recovery of BSCVA. Night halos remained a significant problem in a subset of patients due to the small ablation zone size.

Effect of excimer laser beam delivery and beam shaping on corneal sphericity in photorefractive keratectomy

Purpose: To evaluate the impact of beam delivery and beam shaping on corneal profiles after myopic excimer laser photorefractive keratectomy (PRK). Setting: Department of Ophthalmology, Charité-Campus Virchow Hospital, Humboldt University of Berlin, Berlin, Germany. Methods: Standard myopic 193 nm excimer laser PRK of −3.0 diopters (D) and −6.0 D was performed in porcine eyes using 2 commercially available broad-beam lasers with band-mask and fractal-mask beam shaping, 2 flying-spot lasers, and a scanning-slit laser. A silicone replica was obtained to preserve the corneal profile and was measured with a dynamic focusing topometry system. Results: The scanning-slit and flying-spot lasers created uniform profiles comparable to those in an untreated control group. Both broad-beam lasers with band-mask and fractal-mask beam shaping created central islands and paracentral profile valleys of 15.10 μm and 17.00 μm maximum height after −3.0 D PRK and 26.45 μm and 24.31 μm after −6.0 D PRK. An anti-central-island program, which applied a series of laser pulses centrally to compensate for the central profile elevations, did not eliminate the islands. Stromal surface roughness increased with ablation depth and was significantly worse after scanning-slit ablation than after broad-beam ablation. Conclusions: Laser-induced deviations from the intended uniform corneal profiles were associated with broad-beam ablation and increased ablation depth and therefore lessened the predictability of the refractive outcomes. Scanning-slit and flying-spot systems produced predictably uniform corneal profiles.

Photorefractive keratectomy for myopia with a 15 Hz repetition rate

PurposeTo evaluate excimer laser photorefractive keratectomy (PRK) for myopia using a repetition rate of 15 Hz instead of 10 Hz. SettingThe Cornea and Laser Eye Institute, Teaneck, and Department of Ophthalmology, UMDNJ–New Jersey Medical School, Newark, New Jersey, USA. MethodsPhotorefractive keratectomy using a 15 Hz repetition rate was performed in 23 eyes of 14 patients by a single surgeon at 1 center. The attempted corrections ranged from –2.8 diopters (D) to –5.5 D. Preoperative and postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), predictability, corneal haze, and subjective glare/halo were evaluated over 6 months. ResultsAt 6 months, UCVA was 20/32 or better in all eyes and at least 20/20 in 14 eyes (73.7%). Two eyes (10.5%) lost 2 or more Snellen lines of BSCVA; postoperative BSCVA was at least 20/25 in 100% of eyes and 20/20 or better in 95.0%. Fifteen eyes (78.9%) were within ±0.5 D of attempted correction, and 19 (100%) were within ±1.0 D. Mean spherical equivalent refraction was –4.62 D preoperatively, +0.15 D at 1 month, –0.09 D at 3 months, and –0.37 D at 6 months. At 6 months, 4 eyes (21.0%) had no corneal haze and 14 (73.7%) had trace subepithelial haze. Fifteen eyes (78.9%) had no glare/halo effect at 6 months, and 4 (21.0%) had minimal glare/halo effect. ConclusionsClinical outcomes after excimer laser PRK for myopia using an increased repetition rate of 15 Hz were good and similar to those in studies conducted with a 10 Hz repetition rate.

The Relationship between Rabbit Corneal Opacity and Immunohistochemical Expression of Heat Shock Protein 72/73 and c-fos after Excimer Laser Photorefractive Keratectomy

To evaluate the etiology of corneal opacities, a study was done on the immunohistochemical staining for heat shock protein (HSP) 72/73 and c-fos after myopic excimer laser photorefractive keratectomy (PRK). New Zealand white rabbits (60 eyes) were divided into four groups: –6-, –9- and –15-dpt operation groups and a control group (only corneal epithelium removed). Using an excimer laser (VisX 20/20, Sunnyvale, Calif., USA), myopic PRK was performed on the rabbit’s cornea by a single or multizone technique followed by an immunohistochemical stain to detect the expression of HSP 72/73 and c-fos at 6, 24, 48 h, 1 week and 8 weeks. Corneal epithelia were healed within 3 days in all groups, and 8 weeks after the operation, the mean density of corneal opacity was 0.83 (–6-dpt operation group), 1 (–9-dpt operation group) and 1.67 (–15-dpt operation group). All groups exhibited HSP 73 in corneal epithelium and stroma. However, the maximal expression of c-fos and HSP 72 appeared in corneal epithelium at 24 and 48 h, respectively, after the operation in the –15-dpt group. These results suggest that the expressions of HSP 72 and c-fos in rabbit corneal epithelium are significant factors in relation to corneal opacity after excimer laser PRK.

Corneal hydration and central islands after excimer laser photorefractive keratectomy

Purpose: To determine whether uneven corneal surface hydration during excimer laser photorefractive keratectomy (PRK) is related to postoperative occurrence of central islands.Setting: LSU Eye Center, New Orleans, Louisiana, USA.Methods: A retrospective study reviewed intraoperative videotapes and postoperative videokeratography of 49 eyes of 49 patients who had excimer laser PRK for myopia. The uniformity of corneal hydration within the photoablation zone, particularly the frosty appearance of the ablated zone, was characterized. The presence or absence of a topographic central island (steepening of at least 3.0 diopters and 1.5 mm in diameter) was determined from the 1 month postoperative videokeratographs.Results: Twelve eyes (24,5%) developed central islands postoperatively. A statistically significant association was observed between the uneven surface hydration (central accumulation of fluid) within the ablation zone intraoperatively and the formation of central islands postoperatively (P < .001, Kruskal-Wallis test; Kendall ,r rank correlation = 0.534; P < .001).Conclusion: Nonuniform fluid distribution during photoablation was a risk factor for central island formation after PRK. Intraoperatively, the presence of excess fluid in the central cornea appeared as a shiny area. This mirror-like surface layer may reduce the rate of central ablation by reflecting and absorbing a significant amount of the incident excimer laser light.

Discussion by Peter J. McDonnell, MD

Drs. Rozsı́val and Feuermannová address the problem of patients undercorrected after excimer laser myopic photorefractive keratectomy. Their study addresses the issue of whether these patients can be reablated successfully with a satisfactory outcome in terms of efficacy and safety.

Epithelial debridement for secondary hyperopia following myopic excimer laser photorefractive keratectomy

Background: To evaluate epithelial debridement for the treatment of persistent hyperopia in eyes that had photorefractive keratectomy (PRK).Setting: Optimax Laser Eye Clinics, Manchester, London, Bristol, England.Methods: Epithelial debridement was performed on 46 eyes to reduce the hypermetropia following excimer laser PRK.Results: Mean age of the patients was 43 years ± 9.7 (SD). Mean refractive change was −0.51 diopter (D) ± 0.76 (range +0.75 to −2.50 D). Mean change in best corrected visual acuity (BCVA) was 0.00 Logmar units (range +0.40 to −0.20 units), although 33% of eyes lost one line or more of Logmar BCVA. Mean follow-up after debridement was 61.0 ± 26.9 weeks (range 26 to 140 weeks).Conclusions: Epithelial debridement is an unpredictable procedure to treat secondary hyperopia after PRK, producing a small mean change in spherical equivalent with a wide range of results. A significant number of eyes lost one line or more of Logmar BCVA. We therefore do not advocate epithelial debridement after PRK.

Effect of myopic excimer laser photorefractive keratectomy on the electrophysiologic function of the retina and optic nerve

Purpose: To assess by electrophysiologic testing the effect of photorefractive keratectomy (PRK) on the retina and optic nerve.Setting: Eye Clinic, S. Salvatore Hospital, L'Aquila University, Italy.Methods: Standard pattern electroretinograms (P-ERGs) and standard pattern visual evoked potentials (P-VEPs) were done in 25 eyes of 25 patients who had myopic PRK for an attempted correction between 5.00 and 15.00 diopters (D) (mean 8.00 D). Testing was done preoperatively and 3, 6, 12, and 18 months postoperatively. The contralateral eyes served as controls. During the follow-up, 3 patients (12%) developed steroid-induced elevated intraocular pressure (IOP) that resolved after corticosteroid therapy was discontinued.Results: No statistically significant differences were seen between treated and control eyes nor between treated eyes preoperatively and postoperatively.Conclusion: Myopic excimer laser PRK did not seem to affect the posterior segment. The transient steroid-induced IOP rise did not seem to cause functional impairment.

Efficacy and safety of topical diclofenac in reducing ocular pain after excimer photorefractive keratectomy

Purpose: To evaluate the efficacy and safety of diclofenac sodium 0.1% ophthalmic solution in patients having myopic photorefractive keratectomy (PRK).Setting: Corneal Laser Centre, Clatterbridge Hospital, Wirral, United Kingdom.Methods: We performed a prospective, randomized, double-masked, parallel-group, placebo-controlled study of 50 patients (diclofenac 25, placebo 25) of both sexes who had myopic excimer laser PRK. Results were evaluated by several types of questionnaires and comprehensive clinical examination on the day of the procedure and 1 and 3 to 14 days postoperatively.Results: Diclofenac-treated patients experienced significantly less photophobia, burning/stinging, and ocular pain and took significantly fewer oral narcotic analgesics over the first 24 hours postoperatively than placebo-treated patients.Conclusion: Topical diclofenac significantly reduced the ocular pain and discomfort immediately after excimer PRK without any clinically significant complications or adverse effects.

Corneal asphericity and its implications for photorefractive keratectomy: a mathematical model.

Several clinical trials investigating myopic excimer laser photorefractive keratectomy (PRK) report an initial change in refraction from myopia to hyperopia, followed by a gradual regression toward emmetropia and occasionally to recurrent myopia. We examined the effect of corneal shape on refraction following PRK for myopia using a mathematical model. We calculated the volume of corneal tissue removed by PRK for -3.00-diopter (D) and -6.00-D corrections with ablation diameters of 5 mm and 6 mm. For all the operating algorithms, the central region of the cornea was considered spherical. Mathematical models were developed based on calculations of the apical radius of the ablated cornea and the final refraction for a range of corneal asphericities. Baker's equation was used to model corneal asphericity. The smaller both the ablation size and desired correction, the smaller the effect of corneal asphericity on the refractive outcome. While corneal asphericity can influence the immediate refraction after PRK, the maximum effect is unlikely to be greater than +0.75 D. Corneal asphericity marginally affects the initial outcome of PRK. The effect will probably be offset by the healing response of the cornea.

Scheimpflug anterior segment photography assessment of wound healing after myopic excimer laser photorefractive keratectomy

Purpose: To describe a method for analyzing Scheimpflug anterior segment images for a new measure of the cornea's response to excimer laser photoablation.Setting: Mericos Eye Institute, Scripps Memorial Hospital, La Jolla, California.Methods: Digitized Scheimpflug anterior segment photographs of operated and unoperated eyes were obtained in 17 patients 1 to 15 months after photorefractive keratectomy (PRK). The images were analyzed to determine their dimensions. Each imaged opacity was compared with corneal haze observed by slitlamp biomicroscopy, intended ablation depth, postoperative corneal thickness, and refractive error change.Results: All postoperative corneas displayed a nonhomogeneous, meniscus-shaped pattern in the ablated area that ranged from 17 to 40% of corneal thickness. This pattern correlated poorly with intended laser ablation depth.Conclusion: This technique provides a new assessment of corneal response to PRK. Improvements in software analysis may facilitate quantitative assessment.

The human corneal endothelium after myopic excimer laser photorefractive keratectomy immediate to one-month follow-up.

To assess whether excimer laser photorefractive keratectomy for myopia (PRK) induced any changes in the human corneal endothelium in the immediate postoperative period and up to one month after surgery. No-contact wide-field specular biomicroscopy of the central corneal endothelium was performed on 56 eyes of 56 patients (age 20-54 years, mean 31.3) who underwent photorefractive keratectomy for the correction of myopia ranging between 1.25 and 12.50 D (5.71 +/- 2.96 D, mean +/- SD). Images of the endothelium were obtained using the NonCon Robo endothelial biomicroscope (Konan, Hyogo, Japan), and processed to calculate the mean cell density (MCD), the coefficient of variation of cell area (CV), and the percentage of hexagonal cells (Hex%). Eyes were evaluated immediately before (preop) and after surgery (day 0), on the first two postoperative days (days 1 and 2), and after one month. MCD was 2645 +/- 344 cells/mm2 at preop, 2609 +/- 293 cells/mm2 on day 0, 2681 +/- 320 cells/mm2 on day 1, 2629 +/- 305 cells/mm2 on day 2, and 2709 +/- 308 cells/mm2 at one month; a significant difference was found only comparing preoperative to one month data (p = 0.009). CV was 31.6 +/- 4.7 at preop, 39 +/- 7.1 on day 0 (p = 0.000001), 37.1 +/- 7.8 on day 1 (p = 0.00005), 43.4 +/- 13.1 on day 2 (p = 0.000001), and 34.7 +/- 5.8 on one month (p = 0.0006). Hex% was 61.9 +/- 7.1 at preop, 58 +/- 7.3 on day 0 (p = 0.002), 58.5 +/- 8.5 on day 1 (p = 0.015), 57.1 +/- 8.5 on day 2 (p = 0.00004), and 59.3 +/- 7.5 at one month (p = 0.002). No correlations were found between ablation depth and endothelial changes. Endothelial cell density was not reduced by PRK in the immediate postoperative period. Changes in morphological indices like CV and Hex% indicate that the photoablation causes some kind of damage to the endothelial cells.

Stereopsis and Accommodation Following Photorefractive Keratectomy (PRK) for Myopia

Objective: To study the effect of excimer laser photorefractive keratectomy (PRK) for myopia on accommodation and stereopsis. Study Design: Myopes treated with Summit Technology UV 200 excimer laser PRK were followed prospectively for a mean period of 13 months (range, 9–16 months). Setting: The Laser Unit of the Mater Private Hospital, Dublin, Republic of Ireland. Patients: Twenty-one patients with a mean age of 25.95 years (range, 20–33 years) and a mean refractive error of −3.80 D (range, −1.50–6.00 D) underwent excimer laser PRK for myopia. Mean prelaser amplitude of accommodation (AA) was 10.0 D (range, 8–13). Mean prelaser near stereopsis was 52 second of are (range, 40–140) and mean distant stereopsis was 143 second of arc (range, 30–240). Main Outcome Measures: AA, near and distant stereopsis, accommodative convergence/accommodation (AC/A) ratio and ocular alignment were assessed preoperatively and at 3 and 12 months postoperatively. Nine of the 21 patients underwent PRK in their 2nd eye and had these measurements carried out 3 months following the 2nd treatment. Subjective complaints of asthenopic or presbyopic symptoms were recorded. Results: No patients complained of asthenopic or presbyopic symptoms. Only 3 patients (14.28%) had asymptomatic persistent reduction of AA of ≥ 2 D (mean, 3 D). Near stereopsis was reduced by a mean of 88 seconds of arc in 11 patients (52.3%) at the 3 months visit (range, 10–360). Four of those affected (36.3%) regained their preoperative near stereopsis spontaneously by the end of the study follow-up period and 4 others (36.3%) 3 months following treatment of the 2nd eye. Distant stereopsis was reduced by a mean of 103 seconds of arc (range, 60–180) in 8 patients (38%). Only those who underwent PRK in the 2nd eye (3 patients) recovered their preoperative distant stereopsis. No change in AC/A ratio or ocular alignment was noted in any case. Significantly greater numbers of patients recovered distant stereopsis following treatment of the 2nd eye than recovered it spontaneously ( P = 0.01, tailed value). There was no such significant difference for near stereopsis. Conclusions: Binocular function is disturbed in half those undergoing PRK for myopia for their 1st eye. Despite this, no patients complained of asthenopia or reduced binocular function. Treatment of the fellow eye restored near and distant stereopsis in all cases studied.

Corneal Endothelium After Myopic Excimer Laser Photorefractive Keratectomy

We congratulate Carones et al 1 on their work published in the July 1994 issue of theArchivestitled Corneal Endothelium After Myopic Excimer Laser Photorefractive Keratectomy. Their article confirms our findings reported at the Congress of the European Society of Cataract and Refractive Surgery in September 1993. 2 Excimer laser photorefractive keratectomy has been established as a predictable, safe, and effective method to treat myopia up to 6.0 diopters (D). Reports of the effect on the corneal endothelium vary in the experimental setting. 3,4 To establish whether routine photorefractive keratectomy, in clinical practice, has any detectable adverse effect on the corneal endothelium, we prospectively examined the endothelial cell counts and morphology of 26 eyes of 26 myopes (ages ranging from 21 to 52 years; mean, 29.8 years) using a noncontact specular microscopy camera (Topcon, Tokyo, Japan). The endothelial photographs from the first and last visits, occurring 6 to