A randomized controlled trial to determine the effectiveness of prism spectacles for patients with age-related macular degeneration.

OBJECTIVE: To determine the effectiveness of prism spectacles in people with age-related macular degeneration by relocating the retinal image. METHODS: We implemented a randomized, placebo-controlled, double-masked trial. Participants with age-related macular degeneration received a standard low-vision assessment and the prescription of conventional low-vision aids 6 weeks before the study intervention. Participants were randomized to receive 1 of the following, including the optimal refractive correction: (1) custom, incorporating bilateral prisms to match participants' preferred power and base direction; (2) standard, incorporating standard bilateral prisms (6 prism diopters [Delta] base up for logMAR [logarithm of the minimum angle of resolution] visual acuity (VA) of 0.48-1.00 and 10Delta base up for logMAR VA of 1.02-1.68); or (3) placebo, consisting of spectacles matched in weight and thickness to prism spectacles but without prism. MAIN OUTCOME MEASURES: Outcomes measured binocularly at baseline and 3-month follow-up included distance logMAR VA, reading speed, critical print size, visual functioning questionnaires, and observed visual task performance. Scores on the 25-item National Eye Institute Visual Functioning Questionnaire and the Melbourne Low-Vision ADL (Activities of Daily Living) Index were converted to linear estimates using Rasch analysis. The Manchester Low Vision Questionnaire was used to collect descriptive data. RESULTS: A total of 225 participants completed the trial (median age, 81 years). We found no significant effect of treatment group on any of the outcome measures, including VA, the primary outcome (adjusted for baseline) (P = .63). Participants' responses to the Manchester Low Vision Questionnaire suggested that the prism spectacles added to their problems. CONCLUSIONS: Prism spectacles are no more effective than conventional spectacles for people with age-related macular degeneration.