Photorefractive keratectomy for low myopia at 5 mm treatment diameter. A comparison of two excimer lasers

The aim of the study was to evaluate the algorithm and surgical performance of two excimer lasers, the Summit Excimed 200 LA and the VISX 20/20, by assessing visual outcome parameters such as visual acuity and contrast sensitivity, and subjectively estimating dark vision performance. Furthermore, refractive results and centration of the surgically ablated area were assessed. Twenty patients were included in each group. The indications were myopia between -2 to -5 diopters allowing up to -0.75 diopters astigmatism. The treatment diameter was 5 mm. The postoperative treatment was topical dexamethasone for 3 months. The follow-up time was 12 months. The results showed a median refraction +/- 0.0 D in the Summit group and -0.5 D in the VISX group 12 months postoperatively. The uncorrected visual acuity was 0.5 (20/40) or better for 100% of the Summit treated eyes, whereas 85% of the VISX treated eyes achieved 0.5 (20/40) or better. The other visual qualities as contrast sensitivity, dark vision and centration of the ablation zone were the same in both groups. The slightly more myopic outcome of the VISX laser explains the poorer average uncorrected visual acuity in this group. We have, as a result of the refractive results, changed our algorithm in the VISX machine to achieve emmetropia. It is our experience that one should try to reach emmetropia in this young population.