Monocular versus binocular visual acuity as measures of vision impairment and predictors of visual disability

PURPOSE. TO examine the relationship between monocular and binocular visual acuities as predictors of visual disability in a population-based sample o f individuals 65 years of age and older. METHODS. TWO thousand five hundred twenty community-dwelling residents of S alisbury, Maryland, between the ages of 65 and 84 years of age were recruit ed for the study. Corrected visual acuity was measured monocularly and bino cularly using ETDRS charts. Reading speed, face discrimination, and self-re ported difficulty with visual tasks were also determined. RESULTS. Binocular acuity is predicted with reasonable accuracy by acuity i n the better eye along but not by the widely used American Medical Associat ion (AMA) weighted-average algorithm. The AMA algorithm significantly under estimates binocular acuity when the interocular acuity difference exceeds o ne line. Monocular acuity and binocular acuity were significantly better pr edictors of reading speed than the AMA weighted score or a recently propose d Functional Vision Score (FVS). Monocular acuity in the better eye, binocu lar acuity, and the AMA and FVS algorithms were equally good predictors of self-reported vision disability. None of the acuity measures were good pred ictors of face recognition ability. CONCLUSIONS. The binocular acuities of older individuals can be inferred fr om measures of monocular acuity. There is little evidence for binocular inh ibition when the monocular acuities in the two eyes are unequal, as opposed to the widely used AMA algorithm for computing binocular visual impairment . For tasks that are strongly associated with visual acuity, such as readin g, this association can be captured from measures of monocular acuity and d oes not require separate assessment of binocular acuity.