Comparison of Unaided and Aided Visual Acuity in Adults With Down Syndrome.

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Individuals with Down syndrome (DS) have reduced visual acuity (VA), even when wearing refractive correction. The relationship between refractive error and VA in adults with DS is explored. Thirty adults with DS (age = 29 ± 10 years) were enrolled in a trial comparing clinical and objectively determined refractions. Monocular VA was recorded unaided and aided with best refraction. Vectors M, J0, and J45 were calculated from unaided wavefront aberration measures at the habitual pupil size. The square root of the sum of the squared vectors was calculated providing a single positive vector length representing unaided refractive error. Residual refractive error was determined after applying the best performing refraction. Linear regression determined correlation between refractive error and VAs. Unaided and aided VAs ranged from 0.22 to 1.42 logMAR and 0.06 to 0.82 logMAR, respectively. Unaided and residual refractive error represented as vector length ranged from 0.68 diopters (D) to 13.76D and 0.05D to 1.87D, respectively. Unaided refractive error and VA were significantly positively correlated (r2 = 0.776, P < 0.001), but not residual refractive error and VA (r2 = 0.005, P = 0.721). There was a positive correlation between unaided VA and refractive error magnitude in adults with DS; however, unaided VA was better than expected given the high levels of refractive error. Aided VA and residual refractive error were not correlated, despite overall low levels of remaining residual refractive error, suggesting that factors in addition to optical quality may be limiting VA in this population. Understanding the relationship between refractive error and VA in individuals with DS may provide clinicians clearer expectations for the acuity end points before and after correction for this patient population.