Change in intraocular pressure in myopic eyes measured with contact and non-contact tonometers after laser in situ keratomileusis.

PURPOSE: To study the change in the intraocular pressure (IOP) after laser in situ keratomileusis (LASIK) for correction of myopia. METHODS: One hundred twenty consecutive myopic eyes (60 patients) were included in a prospective study. All eyes received LASIK with the Nidek EC-5000 excimer laser and the Chiron Automated Corneal Shaper. Baseline refraction, keratometry, pachymetry, ablation depth, and IOP measured by Goldmann applanation tonometry and non-contact air puff tonometry were correlated with the IOP change after surgery. Sixty healthy eyes of 30 subjects served as controls. RESULTS: At 6 months, 108 eyes (90%) were examined. Compared to preoperative values, IOP decreased in 103 eyes (95.4%) when measured with applanation tonometry; it decreased in all eyes when measured with air puff tonometry. Mean change in IOP was -4.3 +/- 2.1 mmHg (range, -10.0 to +1.0 mmHg) with the applanation and -6.1 +/- 2.3 mmHg (range, -12.0 to -1.0 mmHg) with air puff tonometry. The IOP change measured with either instrument correlated significantly with the baseline IOP (P < .001) and the ablation depth (air puff, P < .001, applanation; P = .006). CONCLUSION: Intraocular pressure decreased significantly after LASIK when measured with either Goldmann (mean 4.3 mmHg) or air puff (mean 6.1 mmHg) tonometers. This decrease may delay the diagnosis or affect the management of future glaucoma that may develop in a myopic eye that received LASIK.

Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis.

PURPOSE: To compare changes in the corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. METHODS: In a prospective randomized study, 22 patients with bilateral myopia received photorefractive keratectomy on one eye and laser in situ keratomileusis on the other eye. The procedure assigned to each eye and the sequence of surgery for each patient were randomized. Corneal topography measurements were performed preoperatively, 2 and 6 weeks, 3, 6, and 12 months after surgery. The data were used to calculate the wavefront aberrations of the cornea for both small (3-mm) and large (7-mm) pupils. RESULTS: Both photorefractive keratectomy and laser in situ keratomileusis significantly increased the total wavefront aberrations for 3- and 7-mm pupils, and values did not return to the preoperative level throughout the 12-month follow-up period. For a 3-mm pupil, there was no statistically significant difference between photorefractive keratectomy and laser in situ keratomileusis at any postoperative point. For a 7-mm pupil, the post-laser in situ keratomileusis eyes exhibited significantly larger total aberrations than the post-photorefractive keratectomy eyes, where a significant intergroup difference was observed for spherical-like aberration, but not for coma-like aberration. This discrepancy seemed to be attributable to the smaller transition zone of the laser ablation in the laser in situ keratomileusis procedure. Before surgery, simulated pupillary dilation from 3 to 7 mm caused a five- to six-fold increase in the total aberrations. After surgery, the same dilation resulted in a 25- to 32-fold increase in the photorefractive keratectomy group and a 28- to 46-fold increase in the laser in situ keratomileusis group. For a 3-mm pupil, the proportion of coma-like aberration increased after both photorefractive keratectomy and laser in situ keratomileusis. For a 7-mm pupil, coma-like aberration was dominant before surgery, but spherical-like aberration became dominant postoperatively. CONCLUSIONS: Both photorefractive keratectomy and laser in situ keratomileusis increase the wavefront aberrations of the cornea and change the relative contribution of coma- and spherical-like aberrations. For a large pupil, laser in situ keratomileusis induces more spherical aberrations than photorefractive keratectomy. This finding could be attributable to the smaller transition zone of the laser ablation in the laser in situ keratomileusis procedure.

Comparison of photorefractive keratectomy with excimer laser in situ keratomileusis in correcting low myopia (from -2.00 to -5.50 diopters). A randomized study.

OBJECTIVE: To compare laser in situ keratomileusis (LASIK) with photorefractive keratectomy (PRK) in the correction of myopia from -2.00 to -5.50 diopters. DESIGN: Prospective, randomized, paired clinical trial. PARTICIPANTS: Fifty-two eyes of 26 myopic patients were enrolled in the study. INTERVENTION: Each patient received PRK on one eye (PRK eye) and LASIK on the other (LASIK eye); the procedure assigned to each eye, and the sequence of surgeries for each patient was randomized. MAIN OUTCOME MEASURES: Slit-lamp microscopy, manifest refraction, uncorrected and spectacle-corrected visual acuity, and videokeratography were done before operation, and 2 weeks, 6 weeks, 3 months, 6 months, and 12 months after operation. Patient satisfaction and preference were assessed by a subjective questionnaire. RESULTS: All LASIK eyes had fast, painless recovery. At 1 year, 24 patients (92.3%) were examined, the mean spherical equivalent refraction was -0.08 +/- 0.38 diopter in the PRK eyes and -0.14 +/- 0.31 diopter in the LASIK eyes, and the uncorrected visual acuity was 20/20 or better in 15 PRK eyes (62.5%) and 19 LASIK eyes (79.2%); no eye lost 2 or more Snellen lines of spectacle-corrected visual acuity. Both procedures were stable throughout the first year. One PRK eye developed dense subepithelial corneal haze. The strongest correlate to spectacle-corrected visual acuity after the two procedures was the coefficient of variation of corneal power over the pupil. Nineteen patients (79.2%) preferred the LASIK procedure because of the fast, painless recovery. CONCLUSIONS: In the current study, PRK and LASIK were found to be similarly effective, predictable, stable, and reasonably safe for the correction of myopia between -2.00 and -5.50 diopters. Laser in situ keratomileusis has the advantage of fast, painless recovery. Patients prefer LASIK.

Prospective bilateral study of night glare after laser in situ keratomileusis with single zone and transition zone ablation.

PURPOSE: Evaluation of night glare after excimer laser in situ keratomileusis (LASIK) using two different ablation zone diameters. METHODS: One hundred and twenty eyes of 60 consecutive myopic patients received LASIK with the Nidek EC-5000 excimer laser. Eyes were randomized so that every patient had a single ablation zone of 5.5 mm on one eye and an ablation zone of 5.5 mm with a transition zone of 1.0 mm diameter larger on the other eye. Night glare was measured by two methods; a spot light test and a subjective questionnaire. RESULTS: At 6 months, 54 patients (90%) were examined; results of the spot light test showed that 40 patients (74.1%) perceived more glare with the eye with the single ablation zone; the subjective questionnaire indicated that 22 patients (40.7%) had more night glare with the eye with a single ablation zone compared to the other eye. The use of the transition zone increased the required total ablation depth by 20%. CONCLUSION: The use of a peripheral transition 1.0 mm diameter larger than the ablation zone significantly decreased night glare after LASIK with slight increase in the required central ablation depth.

Excimer laser in situ keratomileusis to correct compound myopic astigmatism.

PURPOSE: We studied the efficacy, predictability, stability, and safety of excimer laser in situ keratomileusis (LASIK) to correct myopia and astigmatism. METHODS: We prospectively studied 87 consecutive eyes of 56 patients who received LASIK, divided into two groups: the myopic group included eyes with myopia more than -2.00 diopters (D) and astigmatism less than 0.50 D and the astigmatism group included eyes with myopia of more than -2.00 D and astigmatism of 0.50 D or more. The Chiron automated corneal shaper and the Nidek EC-5000 excimer laser were used in all eyes. A modified personal nomogram was used in all eyes. The changes in refractive sphere and cylinder, and complications were studied at 2 and 6 weeks, 3, 6, and 12 months after surgery. Preoperatively, the mean spherical equivalent refraction was -4.41 D (range, -2.25 to -7.25; SD, 1.74) in the myopia group and -5.79 D (range, -2.25 to -15.50 D; SD, 2.45) in the astigmatism group. The mean spherical component of the refraction was -4.39 D (range, -2.25 to -7.25; SD, 1.74) in the myopia group and -5.19 D (range, -2.00 to -14.00; SD, 2.32) in the astigmatism group. The mean refractive cylinder was 1.19 D (range, 0.5 to 3.00 D; SD, 0.62) in the astigmatism group. RESULTS: At 12 months, 81 eyes (93.6%) of 51 patients were examined; the mean spherical equivalent refraction was -0.43 D (range, +0.50 to -1.25 D; SD, 0.35) in the myopia group and -0.33 D (range, +1.25 to -2.13 D; SD, 0.52) in the astigmatism group. The mean spherical component of the refraction at 12 months was -0.33 D (range, +0.50 to -1.25 D; SD, 0.33) in the myopia group and -0.17 D (range, +1.50 to -1.50; SD, 0.48) in the astigmatism group. The mean refractive cylinder was 0.19 D (range, 0 to 0.75 D; SD, 0.25) in the myopia group and 0.32 D (range, 0 to 1.25 D; SD, 0.30) in the astigmatism group. The mean change in spherical equivalent refraction between 6 weeks and 12 months after surgery was -0.08 D toward myopia (range, -0.50 to -0.75 D; SD, 0.23) in both groups. No eyes lost two or more lines of spectacle-corrected visual acuity. Patient satisfaction was high in both groups. Complications included undercorrection that necessitated reoperation (three eyes), overcorrection (two eyes), and small disc diameter (one eye). No vision threatening complications were observed. CONCLUSION: LASIK with the Nidek EC5000 laser is effective, reasonably predictable, stable, and safe for correction of compound myopic astigmatism with a spherical component between -2.00 and -14.00 D, and a cylindrical component between 0.50 and 3.00 D using the techniques in this study. Astigmatism is undercorrected with the current algorithm. Correction of higher amounts of astigmatism requires further study.