Stereopsis and Accommodation Following Photorefractive Keratectomy (PRK) for Myopia

Abstract

Objective: To study the effect of excimer laser photorefractive keratectomy (PRK) for myopia on accommodation and stereopsis. Study Design: Myopes treated with Summit Technology UV 200 excimer laser PRK were followed prospectively for a mean period of 13 months (range, 9–16 months). Setting: The Laser Unit of the Mater Private Hospital, Dublin, Republic of Ireland. Patients: Twenty-one patients with a mean age of 25.95 years (range, 20–33 years) and a mean refractive error of −3.80 D (range, −1.50–6.00 D) underwent excimer laser PRK for myopia. Mean prelaser amplitude of accommodation (AA) was 10.0 D (range, 8–13). Mean prelaser near stereopsis was 52 second of are (range, 40–140) and mean distant stereopsis was 143 second of arc (range, 30–240). Main Outcome Measures: AA, near and distant stereopsis, accommodative convergence/accommodation (AC/A) ratio and ocular alignment were assessed preoperatively and at 3 and 12 months postoperatively. Nine of the 21 patients underwent PRK in their 2nd eye and had these measurements carried out 3 months following the 2nd treatment. Subjective complaints of asthenopic or presbyopic symptoms were recorded. Results: No patients complained of asthenopic or presbyopic symptoms. Only 3 patients (14.28%) had asymptomatic persistent reduction of AA of ≥ 2 D (mean, 3 D). Near stereopsis was reduced by a mean of 88 seconds of arc in 11 patients (52.3%) at the 3 months visit (range, 10–360). Four of those affected (36.3%) regained their preoperative near stereopsis spontaneously by the end of the study follow-up period and 4 others (36.3%) 3 months following treatment of the 2nd eye. Distant stereopsis was reduced by a mean of 103 seconds of arc (range, 60–180) in 8 patients (38%). Only those who underwent PRK in the 2nd eye (3 patients) recovered their preoperative distant stereopsis. No change in AC/A ratio or ocular alignment was noted in any case. Significantly greater numbers of patients recovered distant stereopsis following treatment of the 2nd eye than recovered it spontaneously (P = 0.01, tailed value). There was no such significant difference for near stereopsis. Conclusions: Binocular function is disturbed in half those undergoing PRK for myopia for their 1st eye. Despite this, no patients complained of asthenopia or reduced binocular function. Treatment of the fellow eye restored near and distant stereopsis in all cases studied.