Visual outcome of excimer laser photorefractive keratectomy for myopia. A comparison of three laser delivery systems in Australia.

PURPOSE

To compare the performance of the three excimer laser delivery systems in correcting myopia.

METHODS

The first generation excimer laser systems produced by Summit, VISX and LEI were examined. The first 40 consecutive eyes with six-month refractive results were selected from the LEI centre. Forty consecutive eyes, matched for age and attempted corrections, were then selected from each of the Summit and VISX centres. The postoperative visual results were examined retrospectively and compared among the three groups.

RESULTS

At six-month follow-up, the mean and standard deviation of the spherical equivalent refraction 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 group (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 achieved corrections within 1 dioptre of intended corrections (P = 0.131, chi 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 more than 1 dioptre at six-month follow-up. Unaided visual acuity (Snellen 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 eyes (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 Summit 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 visual acuity six months after myopic photorefractive keratectomy. No statistical differences were found between the groups in terms of significant overcorrection or loss of best corrected acuity. The group treated using the Summit system demonstrated significantly greater regression than the other groups, necessitating larger initial hyperopic shifts.