Effect of larger ablation zone and transition zone on corneal optical aberrations after photorefractive keratectomy.

OBJECTIVE: To evaluate the effects of photorefractive keratectomy on corneal optical aberrations using a 5.5-mm optical zone and a 7.0-mm transition zone. METHODS: Videokeratographs of 72 eyes from 47 patients treated for low to moderate (1-9 diopters) myopia were obtained at the preoperative and 1-, 3-, 6-, 12-, and 18-month postoperative examinations. The videokeratoscopy data files were used to calculate the wavefront variance of the corneas for small (3-mm) and large (7-mm) pupils using a previously described method. RESULTS: In general, all optical aberrations decreased postoperatively for 3-mm pupils and increased for 7-mm pupils compared with preoperative values. For 3-mm pupils, the 2 common optical aberrations (comalike [S(3)] and spherical-like [S(4)]) decreased postoperatively and never returned to preoperative values. For 7-mm pupils, however, comalike aberrations increased slightly and spherical-like aberrations increased by nearly an order of magnitude during the postoperative period. Similarly, for 3-mm pupils, the higher order S(5) and S(6) aberrations decreased throughout the postoperative period, with S(6) values showing an approximately 23-fold reduction at 12 and 18 months. For 7-mm pupils, S(5) and S(6) aberrations increased slightly, more so for S(5) (approximately 3-fold) than for S(6). Total wavefront aberrations decreased an average of 2.3 times postoperatively for 3-mm pupils, and increased significantly (P<.05) at all postoperative examinations for 7-mm pupils. Opening the pupil from 3 mm to 7 mm before surgery produced a 14-fold increase in total aberrations, whereas this same change produced an average 113-fold increase after photorefractive keratectomy. CONCLUSIONS: Corneal optical aberrations after photorefractive keratectomy with a larger ablation zone and a transition zone are less pronounced and more physiologic than those associated with first-generation (5-mm) ablations with no transition zone. CLINICAL RELEVANCE: Evaluating the postoperative corneal aberration structure will help us devise ways to minimize the wavefront aberrations of the eye through the creation of an ideal corneal first surface, thereby improving visual results for patients undergoing excimer laser ablations for refractive correction.

Laser in situ keratomileusis for myopia up to -11 diopters with up to -5 diopters of astigmatism with the summit autonomous LADARVision excimer laser system.

OBJECTIVE: To assess the safety and effectiveness of the Summit Autonomous LADARVision active tracking narrow beam excimer laser system for laser in situ keratomileusis (LASIK) correction of myopia and astigmatism. DESIGN: A multicenter, prospective noncomparative case series. PARTICIPANTS: This cohort consisted of 177 eyes corrected for spherical myopia up to -11 diopters (D) and 170 eyes corrected for myopia up to -11 D spherical equivalent with astigmatism up to -5 D. INTERVENTION: Treatments were performed at four sites in the United States using a 6-mm optic zone for spherical myopes and a 5.5-mm optic zone with a 1-mm blend for astigmats. MAIN OUTCOME MEASURES: Visual acuity, subjective refraction, vector analysis, subject satisfaction, intraocular pressure, complications, and adverse reactions. RESULTS: Six-month follow-up was available on 157 spherical eyes and 113 astigmatic eyes. For spherical myopes, uncorrected visual acuity (UCVA) was 20/20 or better in 60.5%, 20/25 or better in 80.3%, and 20/40 or better in 93.9%. The mean spherical equivalent was -0.29 +/- 0.45 D with 75.2% +/- 0.50 D and 94.9% +/- 1.00 D of intended. A loss of two lines of best spectacle-corrected visual acuity (BSCVA) occurred in 0.6%, and no eyes lost greater than two lines of BSCVA. For astigmatic myopes, UCVA was 20/20 or better in 52.0%, 20/25 or better in 74.5%, and 20/40 or better in 94.1%. The mean spherical equivalent was -0.23 +/- 0.49 D with 75.2% +/- 0.50 D and 95.6% +/- 1.00 D of intended. A loss of two lines of BSCVA occurred in 0.9%, and no eyes lost greater than two lines of BSCVA. Vector analysis showed that 99% of the intended cylinder was corrected on average with a mean angle of error of 4.2 degrees. Refractive stability was achieved between 1 and 3 months in 97.5% of spherical eyes and 99.4% of astigmatic eyes and confirmed between 3 and 6 months in 100% of both spherical and astigmatic eyes. CONCLUSIONS: Eyes treated for myopia up to -11 D of spherical equivalent with or without astigmatism up to -5 D show early refractive stability, good UCVA outcomes, no significant loss of BSCVA, accurate correction of astigmatism, and slight undercorrection without a change from the photorefractive keratectomy algorithm and with a single treatment.

Contrast sensitivity evaluation after laser in situ keratomileusis.

OBJECTIVE: To determine the effects of laser in situ keratomileusis (LASIK) on best-corrected visual acuity (BCVA) and contrast sensitivity. DESIGN: Prospective, observational case series. PARTICIPANTS: One hundred twelve eyes, in 65 patients with myopia and myopia with astigmatism, who underwent LASIK. TESTING AND MAIN OUTCOME MEASURES: Best-corrected visual acuity using the Snellen visual acuity chart and contrast sensitivity using the CSV 1000 (Vector Vision, Dayton OH) was tested before surgery and 1 week, 1 month, and 3 months after surgery in patients who underwent LASIK. RESULTS: Contrast sensitivity was depressed for patient eyes with spherical equivalence (SE) between -1.25 diopters (D) and -13.75 D, at 12 cycles/degree for at least 3 months and at 18 cycles/degree for 1 week after LASIK. For patient eyes with SE between -1.25 D and -6.00 D, contrast sensitivity was depressed only at 12 cycles/degree for at least 3 months after LASIK. For patient eyes with SE between -6.00 D and -13.75 D, contrast sensitivity was depressed at 6, 12, and 18 cycles/degree 1 week after LASIK but returned toward preoperative levels by 1 month after surgery. Despite the slight decreases in contrast sensitivity, all scores were still within the range of normal values except for 12 cycles/degree for 3 months and 18 cycles/degree at 1 week after surgery in the high myopia group. Although highly myopic patients, compared with patients with low myopia, had slightly less BCVA before surgery, both groups maintained their preoperative BCVA at all postoperative visits. CONCLUSIONS: Based on this study, we conclude that LASIK has little effect on BCVA and contrast sensitivity for up to 3 months after surgery.

Efficacy of abciximab readministration in coronary intervention.

Abciximab, an Fab monoclonal antibody fragment that blocks the platelet glycoprotein IIb/IIIa receptor, is increasingly used as an adjunct to coronary intervention. Little is known, however, about the efficacy and safety of readministration of abciximab. This study examined and characterized outcomes of patients receiving abciximab for a second time. From April 1995 to June 1997, 164 consecutive patients were readministered abciximab at our 3 institutions. We retrospectively examined and analyzed in-hospital outcomes in this cohort. The median time to readministration was 95 days. The angiographic success rate of percutaneous intervention was 99.5%. Rates and 95% confidence intervals of in-hospital events were death 2% (0.7% to 6.1%), myocardial infarction 3% (1% to 7%), coronary bypass surgery 0% (0% to 2.2%), and intracranial hemorrhage 2% (0.4% to 5.3%). Severe thrombocytopenia was observed in 4% of patients (1.4% to 7.8%) after readministration. Allergic or anaphylactic reactions were not observed. Major bleeding was associated with excessive concomitant antithrombotic therapy. Patients undergoing readministration of abciximab within 2 weeks of first administration experienced a higher incidence of severe thrombocytopenia (12% vs. 2%, p = 0.046). Thus, abciximab remains clinically efficacious when readministered as an adjunct to percutaneous coronary intervention. However, concomitant heparin administration must be carefully monitored and warfarin therapy should be avoided. Vigilant surveillance for thrombocytopenia should be employed. Reduced dosing may be necessary when abciximab is readministered within days of the initial administration.

Comparison of ketorolac tromethamine, diclofenac sodium, and moist drops for ocular pain after radial keratotomy.

PURPOSE: To compare the 2 most popular commercially available topical nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of ocular pain following radial keratotomy (RK). SETTING: Multicenter clinical trial. METHODS: Ninety-seven RK patients were randomly assigned to 1 of 3 treatment groups: ketorolac tromethamine, diclofenac sodium, and moist drops as a control. The patients used 1 drop of the masked medication and 1 drop of ofloxacin 3 times a day for 3 days prior to surgery. They received 1 drop of the masked medication 1 hour before surgery, immediately after surgery, and 4 times a day thereafter. Patients were given a written questionnaire preoperatively and were also instructed to call a central computerized telephone system to answer prerecorded questions about ocular comfort. The calls were placed 30 minutes and 1, 2, 3, 4, 5, 6, 24, and 48 hours after surgery. RESULTS: Two hundred ten statistical values were calculated to compare symptoms in the unoperated eye at baseline with symptoms in the operated eyes at each of 9 postoperative time points. Only 7 of the 210 values (3.3%) were significantly different among patient groups (operated versus unoperated eyes) by psychometric testing. CONCLUSIONS: Both ketorolac tromethamine and diclofenac sodium were more effective in reducing post-RK discomfort than the control (moist artificial tears). Given the large number of tests and the small number that tested as significant, the significant differences (7 of 210 measurements) observed among the 3 treatment groups probably occurred by chance, although the improved foreign-body sensation, functionality, and compliance scores in the ketorolac group during the first 4 hours might be clinically important.

Photorefractive keratectomy for low-to-moderate myopia and astigmatism with a small-beam, tracker-directed excimer laser.

OBJECTIVE: To assess the safety and effectiveness of the Autonomous Technologies Corporation LADARVision excimer laser system for photorefractive keratectomy correction of myopia and astigmatism. DESIGN: A multicenter, prospective, noncomparative case series. PARTICIPANTS: The cohort consisted of 467 eyes corrected for spherical myopia and 211 eyes corrected for myopia with astigmatism. INTERVENTION: Treatments were performed at six sites in the United States using a 6-mm ablation zone for spherical myopes and a 5.5-mm zone with a 1.0-mm blend for astigmats. MAIN OUTCOME MEASURES: Visual acuity, subjective refraction, corneal haze, intraocular pressure, complications, adverse reactions, patient satisfaction, and corneal endothelial changes. RESULTS: Twelve-month follow-up was available on 414 spherical eyes and 175 astigmatic eyes. The results for spherical eyes with correction between -1 and -5.99 diopters (D) were: uncorrected visual acuity (UCVA) of 20/40 or better achieved by 98.1%, 20/20 or better by 72%, 1.8% lost 2 lines and 0.3% lost greater than 2 lines of best spectacle-corrected visual acuity (BSCVA); 76.4% were within 0.50 D of the target correction and 94.4% were within 1.00 D. The results for myopia with astigmatism with spherical equivalent correction between -1 and -5.99 D were: UCVA of 20/40 or better in 97.4%, 20/20 or better in 61.7%, 2.5% lost 2 lines and no eyes lost greater than 2 lines BSCVA; 73.9% were within 0.50 D of the target correction and 95% were within 1.00 D. For spherical myopes combined with myopic astigmats corrected for 6 to 10 D, results were: UCVA of 20/40 or better in 93.4%, 20/20 or better in 61.2%, 2.3% lost 2 lines and no eyes lost greater than 2 lines of BSCVA; 67.2% were within 0.50 D of the desired correction and 87.8% were within 1.00 D. Refractive stability was achieved between 3 and 6 months for the spherical and astigmatic groups. No eyes had corneal haze graded as moderate or greater, and there was no significant decrease in endothelial cell density. CONCLUSIONS: Patients treated for 1 to 10 D of spherical equivalent myopia, with or without astigmatism, showed early refractive stability, excellent UCVA, no significant loss of BSCVA, no loss of endothelial cell density, and very low levels of corneal haze to 12 months after surgery.

Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study.

PURPOSE: To correlate clinically observed fluctuations in manifest refraction, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patients 10 years after radial keratotomy (RK). SETTING: Four clinical centers in the United States that participated in the Prospective Evaluation of Radial Keratotomy (PERK) study. METHODS: Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 years (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning-to-evening changes in the means of the various clinical and videokeratographic values were assessed using pairwise methods. RESULTS: The mean increase in myopia was 0.36 diopters (D) +/- 0.58 (SD) from morning to evening (P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepening of 0.52 +/- 0.45 D (P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction (R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity (R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings correlated with the change in the manifest spherical equivalent refraction (R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 for average SimK), although the standard clinical keratometric data did not (P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 +/- 1.59, which also correlated with the change in the manifest spherical equivalent refraction (R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean change of -0.97 +/- 3.29 mm Hg), but the difference was not significant. Variations in IOP in individual patients, however, were correlated with changes in the manifest spherical equivalent refraction (R = 0.37, P = .04). CONCLUSIONS: Diurnal fluctuations in corneal topographic indexes can be used to evaluate the diurnal fluctuations in refraction and visual acuity after RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK.

Corneal topography of small-beam tracking excimer laser photorefractive keratectomy.

PURPOSE: To evaluate the topographic characteristic of photorefractive keratectomy (PRK) for low myopia performed with a small-beam (0.9 mm) tracking excimer laser. SETTING: Department of Ophthalmology, LSU Eye Center, Louisiana State University Medical Center School of Medicine in New Orleans, and the Refractive Surgery Center of the South at the Eye, Ear, Nose, & Throat Hospital, New Orleans, Louisiana, USA. METHODS: Sixty-seven eyes of 47 patients had PRK with a small-beam tracking laser. Of these, 49 eyes had data permitting evaluation of ablation centration; usable data for topographic analysis were available for 59 eyes preoperatively, 54 eyes at 1 month, 42 eyes at 3 months, and 25 eyes at 6 months, permitting measurement of various topographic parameters, including the cylinder (CYL), average corneal power (ACP), surface regularity index (SRI), surface asymmetry index (SAI), corneal eccentricity index (CEI), and coefficient of variation of corneal power (CVP). RESULTS: Preoperatively, all eyes were topographically normal. Postoperatively, no eye exhibited a "central island" by even the least-restrictive definition, and all eyes had best spectacle-corrected visual acuities (BSCVAs) of 20/20 or better at all follow-ups. Mean decentration of the ablations from the pupil centers was 0.42 mm +/- 0.28 (SD) (n = 49). There was no correlation between measured decentration and BSCVA (P = .46). The central cornea was flattened (decreased ACP; P < .001) and made oblate (decreased CEI; P < .001) as expected. There was no increase in SRI or SAI (irregular astigmatism) at 6 months compared with preoperative values (P = .91); however, CYL and CVP (varifocality) increased slightly (P = .04 and .02, respectively). CONCLUSION: The absence of significant regular or irregular astigmatism 6 months after PRK with the small-beam laser is an improvement over published results achieved with wide-beam lasers and is consistent with the excellent visual acuity results in this cohort.

Photorefractive keratectomy with a small spot laser and tracker.

BACKGROUND: The Autonomous Technologies LADARVision excimer laser system utilizes an eye tracking mechanism and a small spot for photorefractive keratectomy. METHODS: One hundred and two eyes of 102 patients were treated for -1.50 to -6.25 D of spherical myopia at the spectacle plane using a 6-mm diameter ablation zone. One year follow-up was available for 93 eyes (91%). RESULTS: Uncorrected visual acuity for eyes treated for distance vision was 20/40 or better in 99% (n = 90), and 20/20 or better in 70% (n = 64) of eyes at 12 months. Spectacle-corrected visual acuity was 20/25 or better in all 92 eyes reported; no eye lost more than 2 lines of spectacle-corrected visual acuity, and only 1 eye (1.0%) experienced a loss of 2 lines (20/12.5 to 20/20) at 1 year. The refractive result was within +/- 0.50 D of the desired correction in 75% (n = 70), and within +/- 1.00 D in 93% (n = 86) of eyes at 12 months. Refractive stability was achieved between 3 and 6 months. Corneal haze was graded as trace or less in 100% of the 93 eyes. No significant reductions were noted in contrast sensitivity or endothelial cell density. CONCLUSIONS: Patients treated with the Autonomous Technologies LADARVision excimer laser system for -1.50 to -6.25 D of spherical myopia with 1 year follow-up had uncorrected visual acuity of 20/20 or better in 70%, no significant loss of spectacle-corrected visual acuity, no reduction of endothelial cell density or contrast sensitivity, and low levels of corneal haze.

Comparison of the effectiveness of 4 anti-inflammatory drops in relieving photophobia after pupil dilation.

PURPOSE: To compare the relative effectiveness of diclofenac, flurbiprofen, ketorolac, and prednisolone acetate in relieving photophobia after pupil dilation for fundus examination. SETTING: Eye, Ear, Nose, and Throat Hospital, New Orleans, Louisiana, USA. METHODS: This prospective, blind, placebo-controlled study comprised 105 patients randomly assigned to 1 of 10 treatment groups. Five minutes after instillation of dilating drops, each patient received drops of different test medications in the right and left eyes. Light sensitivity and pupil measurement tests were performed over 2 hours after the pharmacological mydriasis. After photostimulation, patients were asked to rate their photosensitivity on numerical and analog scales and to indicate a filter value required to alleviate right-induced discomfort. Test results were analyzed to detect differences among the pain levels associated with each treatment. RESULTS: There were no significant differences between the placebo and any active treatment drug at any time during the study. CONCLUSION: These findings suggest that mediators other than prostaglandins may have a role in photosensitivity or that increased postmydriatic photosensitivity is a result of higher light levels entering the eye through the dilated pupil.

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 tau 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.

Normal human corneal cell populations evaluated by in vivo scanning slit confocal microscopy.

PURPOSE: To analyze cellular populations in healthy human corneas. METHODS: The study group consisted of 58 eyes of 45 patients with normal corneas. The age distribution was 45 +/- 17 years (mean +/- SD; range, 20-84). Scanning slit confocal microscopy of the central corneas was performed. The images were analyzed visually for cell morphology, and the densities and areas of cells were measured. RESULTS: No statistically significant differences were measured in cell densities or cell areas of any corneal layer between female and male patients (p = 0.22-0.50) nor between right and left eyes (p = 0.16-0.45). The area of superficial epithelial cells was 913 +/- 326 microm2 (mean +/- SD; range, 518-2,112), and the superficial epithelial cell density was 1,213 +/- 370 cells/mm2 (mean +/- SD; range, 473-1,929). The area of basal epithelial cells was 177 +/- 19 microm2 (mean +/- SD; range, 138-242), and the basal epithelial cell density was 5,699 +/- 604 cells/mm2 (mean +/- SD; range, 4,135-7,267). The average apparent keratocyte density was 1,058 +/- 217 cells/mm2 (mean +/- SD; range, 604-1,599) in the anterior stroma, and 771 +/- 135 cells/mm2 (mean +/- SD; range, 493-1,145) in the posterior stroma. The difference in apparent keratocyte densities between the anterior and posterior stroma was statistically significant (p < 0.001). The average endothelial cell area was 334 +/- 51 microm2 (range, 273-553), and the cell density was 3,055 +/- 386 cells/mm2 (mean +/- SD; range, 1,809-3,668). The endothelial cell density had a negative, statistically significant correlation with age (r = -0.68, p < 0.001). The densities of the other corneal cell layers did not have a statistically significant correlation with age. CONCLUSION: In vivo scanning slit confocal microscopy is a useful tool for studying corneal cell populations. Central corneal cell densities were found to decrease significantly with age only in the endothelium. For the first time in human corneas using in vivo confocal microscopy, this study statistically confirms a higher apparent number of keratocytes in the anterior stroma than in the posterior stroma.

In vivo confocal microscopy of Fuchs' endothelial dystrophy.

PURPOSE: The purpose of this study is to analyze in vivo confocal microscopic findings of corneas with Fuchs' endothelial dystrophy. METHODS: Central corneas of 17 eyes of 11 patients aged 41-86 years were examined using in vivo scanning slit confocal microscopy after being diagnosed with Fuchs' endothelial dystrophy. The cellular structure of the corneas was analyzed morphologically and quantitatively and compared to control results from 22 healthy corneas. RESULTS: Bullae were detected in the basal epithelial layer of one eye. Eight of 17 eyes (47%) exhibited an abnormal Bowman's layer: diffuse bright reflection and absence of nerves. Eleven eyes (65%) exhibited abnormal anterior stroma: lacunae and diffuse increased light reflection due to edema. In 12 eyes (71%), lacunae or dark bands 5-20 microm wide against increased background reflection were noted in the posterior stroma. Descemet's membrane was thickened in all eyes. Dark bands were detected in six eyes (35%). Guttae (137-1,231/mm2) 20-40 microm in diameter were found in every endothelial cell layer. The mean endothelial cell count was 1,202 +/- 850 (cells/mm2 +/- SD; range, 0-2,735). There was a positive correlation between endothelial cell counts obtained by specular microscopy and those obtained by confocal microscopy (r = 0.95). CONCLUSION: In vivo confocal microscopic findings of Fuchs' endothelial dystrophy are described for the first time in a series of cases. Pathological changes in Fuchs' dystrophy were detected in all corneal layers, more frequently in the posterior layers. Endothelial cell counts obtained with confocal microscopy were statistically similar to those obtained with standard specular microscopy.

Topographic assessment of irregular astigmatism after photorefractive keratectomy.

OBJECTIVE: To correlate new quantitative topographic indexes of corneal irregular astigmatism to best spectacle-corrected visual acuity (BSCVA) following excimer laser photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, LSU Eye Center, and Refractive Surgery Center of the South, Ear, Nose & Throat Hospital, New Orleans, Louisiana; Manhattan Eye, Ear and Throat Hospital, New York, New York, USA. METHODS: Videokeratography data (TMS-1) were obtained preoperatively and 1, 3, 6, 12, 18, and 24 months postoperatively from 100 eyes having PRK for low to mild myopia. Algorithms measured fine local irregularity with the surface regularity index (SRIp), varifocality with the coefficient of variation of corneal power (CVPp), and central islands with the elevation/depression magnitude (EDM). RESULTS: The SRIp and CVPp increased after surgery and remained significantly higher than the preoperative levels throughout the 24 month follow-up (P < .05). The increase in EDM was significant from 1 to 6 months (P < .05) but not thereafter. Multiple regression analysis revealed that variables having a statistically significant relationship with postoperative BSCVA were CVPp and EDM at 1 month, CVPp at 3 months, and CVPp, haze, and age at 6 months. No statistically significant correlation between any measures of irregular astigmatism and BSCVA was found after 1 year of follow-up. CONCLUSION: The quantitative measures used in this study are sensitive methods by which irregular astigmatism after keratorefractive procedures can be classified, evaluated, and compared.

Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy.

BACKGROUND: Complaints of glare, halos, and disturbances of night vision after photorefractive keratectomy (PRK) probably result from changes in the corneal aberration structure induced by the laser ablation procedure. The purpose of this article is to characterize changes in the corneal aberration structure after PRK and to demonstrate the effect of pupil dilation on these changes. METHODS: Videokeratographs obtained preoperatively (n = 112) and at 1 (n = 94), 3 (n = 103), 6 (n = 91), 12 (n = 60), 18 (n = 53), and 24 (n = 44) months postoperatively from 112 eyes of 89 patients who had undergone PRK for myopia were analyzed. The data were used to calculate the wavefront variance of the cornea for both small (3-mm) and large (7-mm) pupils. RESULTS: For both the 3- and 7-mm pupil, coma-like aberrations increased significantly from preoperative values to 1-month postoperative values (P < .05 and P < .001, respectively); for 7-mm pupils, the postoperative values never returned to preoperative values (P < .001, 24 months). For the 3-mm pupil, spherical-like aberrations decreased significantly 1 month after surgery (P < .001), and never returned to preoperative values. For the 7-mm pupil, spherical-like aberrations increased significantly 1 month after surgery (P < .001) and did not return to preoperative values. Opening the pupil from 3 to 7 mm increased spherical-like aberrations only 7-fold before PRK. After PRK, however, pupillary dilation caused a 300-fold increase in this type of aberration. For both pupil sizes at all times after PRK, the magnitude of the surgically induced aberration correlated with the amount of the attempted correction (P < .001, r2 = 0.6 at 1 month for a 7-mm pupil). CONCLUSIONS: Photorefractive keratectomy increases the wavefront variance of the cornea; PRK changes the relative contribution of coma-like and spherical-like aberrations; after PRK, the diameter of the entrance pupil greatly affects the amount and character of the aberrations; and the magnitude of the aberration increases with the attempted correction. CLINICAL RELEVANCE: Quantitative characterization of irregular astigmatism with the measurement of aberration structures following corneal surgery and the correlation of these data with visual performance in clinical trials provide the basis for understanding patient complaints and for improving surgical approaches. Our analysis shows that, whereas induced aberrations are minimal for simulated day-time vision (3-mm pupil), the increase in aberrations measured for simulated night vision (7-mm pupil) supports the use of large treatment zones to reduce visual disturbances such as glare and halos.

Disparity between keratometry-style readings and corneal power within the pupil after refractive surgery for myopia.

PURPOSE: Because keratometry readings may no accurately reflect the refractive changes after keratorefractive surgery for myopia, better methods for the assessment of corneal curvature in the postsurgical cornea are needed. METHODS: We developed a procedure to calculate the average central power (ACP) of the cornea within the entrance pupil from videokeratography. Videokeratograph-derived keratometry-style readings (average K; K) and calculated ACPs, as well as the differences between the two values, were compared in four groups: normal corneas (n = 30), corneas with regular astigmatism (n = 30); post-radial keratotomy corneas (RK, n = 85), and post-excimer laser photorefractive keratectomy corneas (PRK, n = 63). Intraocular lens (IOL) powers calculated by using K or ACP in the Sanders-Retzlaff-Kraff formula were compared. RESULTS: In the groups with normal corneas or regular astigmatism, none of the eyes showed a difference between K and ACP > 0.25 D. However, six (7%) of the RK eyes and 16 (25%) of the PRK eyes had differences > 0.55 D; in these eyes, the disparity between IOL powers calculated by using K and IOL powers calculated by using ACP was > 0.5 D. CONCLUSION: These results suggest that basing the calculation of IOL powers on keratometry readings in patients who have undergone RK. PRK, or possibly other refractive procedures may result in a residual refractive error in some eyes. In particular, patients undergoing surgery involving a small optical zone or large attempted correction or both, as well as those with low postoperative keratometry readings, may be at risk for this problem if IOL placement becomes necessary in later years.

Near vision contrast sensitivity after photorefractive keratectomy.

BACKGROUND: To evaluate near vision contrast sensitivity as a measure of visual performance after photorefractive keratectomy (PRK). SETTING: LSU Eye Center, New Orleans, Louisiana. METHODS: Using Holladay Contrast Acuity Test cards, near (reading) vision for five levels of contrast sensitivity was evaluated in a cross section of 53 eyes of 31 patients 25 to 732 days after PRK. Twenty-four normal eyes of 22 myopic patients served as controls. RESULTS: Near contrast sensitivity decreased at all tested contrast levels for approximately 7 months after PRK and then returned to baseline. This phenomenon paralleled the fluctuation in best corrected distance Snellen acuity. CONCLUSIONS: These preliminary results indicate that Snellen visual acuity and near contrast sensitivity returned to baseline within 1 year after PRK.

Diclofenac sodium attenuates neural activity after photorefractive keratectomy in rabbits.

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 5-mm diameter, circular PRK ablations with a central depth of 85 microns. 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.