VISUAL OUTCOME OF EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA - A COMPARISON OF 3 LASER DELIVERY SYSTEMS IN AUSTRALIA

Purpose: To compare the performance of the three excimer laser deliver y systems in correcting myopia. Methods: The first generation excimer laser systems produced by Summit, VISX and LEI were examined. The firs t 40 consecutive eyes with six-month refractive results were selected from the LEI centre. Forty consecutive eyes, matched for age and attem pted corrections, were then selected from each of the Summit and VISX centres. The postoperative visual results were examined retrospectivel y and compared among the three groups. Results: At six-month follow-up , the mean and standard deviation of the spherical equivalent retracti on were +0.27 (SD, 0.65) dioptre in the Summit group, -0.33 (SD, 0.83) dioptre in the VISX group and -0.62 (SD, 0.89) dioptre in the LEI gro up (P = 0.0001, ANOVA). Thirty-five eyes (88%) in the Summit group, 33 eyes (83%) in the VISX group and 28 eyes (70%) in the LEI group achie ved corrections within 1 dioptre of intended corrections (P = 0.131, c hi(2) test). Four eyes (10%) in the Summit group, two eyes (5%) in the VISX group and one eye (3%) in the LEI group were overcorrected by mo re than 1 dioptre at six-month follow-up. Unaided visual acuity (Snell en equivalent) was 6/12 or better in 37 eyes (93%) in the Summit group , 34 eyes (85%) in the VISX group and 34 eyes (87%) in the LEI group ( data missing in one eye). Loss of one or more lines of best corrected visual acuity (Snellen equivalent) was found in 6 of 39 eyes (15%) in the Summit group, 10 of 40 eyes (25%) in the VISX group and 4 of 36 ey es (11%) in the LEI group (P = 0.258, chi(2) test). Regression between one and six month follow-up differed significantly (P = 0.001, ANOVA) among the groups, with the mean of -1.25 (SD, 0.94) dioptres in the S ummit group, -0.59 (SD, 1.01) dioptre in the VISX group and -0.40 (SD, 0.99) dioptre in the LEI group. Conclusions: Statistically comparable results were found in the three groups in terms of refraction and vis ual acuity six months after myopic photorefractive keratectomy. No sta tistical differences were found between the groups in terms of signifi cant overcorrection or loss of best corrected acuity. The group treate d using the Summit system demonstrated significantly greater regressio n than the other groups, necessitating larger initial hyperopic shifts .