Treatment of unilateral amblyopia: factors influencing visual outcome.

PURPOSE To identify factors that influence the outcome of treatment for unilateral amblyopia, as a part of the Monitored Occlusion Treatment of Amblyopia Study (MOTAS). METHODS This was an intervention study consisting of three nonoverlapping phases: "Baseline", "refractive adaptation" (18 weeks of full-time spectacle wear), and "occlusion" (6 hours of patching per day, objectively monitored). Condition factors: type of amblyopia, age of participant, initial severity of amblyopia, fixation, and binocular vision status; treatment factors: refractive adaptation and occlusion (total dose [hours] and dose rate [hours per day]) were assessed for their influence on visual outcome. Visual outcome was expressed in three ways: logMAR (logarithm of the minimum angle of resolution) change, residual amblyopia, and proportion of the deficit corrected. RESULTS The study included 85 participants (mean age, 5.1 +/- 1.4 years) with amblyopia associated with strabismus (n = 32) or anisometropia (n = 20) or associated with both anisometropia and strabismus (n = 33). Treatment factors: cumulative occlusion dose exceeding 50 hours, and dose rates > or =1 hour per day resulted in (P < or = 0.01) lower residual amblyopia and a greater proportion of the deficit corrected. Condition factors associated with poor outcome (high residual amblyopia) were presence of eccentric fixation, severe initial amblyopia, and no binocular vision. CONCLUSIONS Factors influencing outcome with treatment for amblyopia are occlusion dose (the rate of delivery and cumulative dose worn), the initial severity of the amblyopia, binocular vision status, fixation of the amblyopic eye, and the age of the subject at the start of treatment.