Variability in autorefraction for subjects with and without Down syndrome

Abstract

Purpose: Patients with Down syndrome (DS) have a high incidence of refractive error and corneal distortion, and a relationship between DS and keratoconus is reported in the literature. Objective measures of refractive error, such as autorefraction, provide a starting point for subjective refraction and may more heavily influence prescribing decisions for this group given the difficulty of performing subjective refraction. This study compares variability in repeated measures of autorefraction in patients with and without DS.

Methods: Grand Seiko autorefraction was performed binocularly on 140 DS subjects (age range: 8 to 55, mean: 25±9 yrs) and 138 control subjects (age range: 7 to 59, mean: 25±10 yrs). Subjects where at least 3 repeated measures were recorded in both eyes (DS: 112 and control: 136) were included in further analysis. Each refraction was converted to power vector notation (M J₀ J₄₅). The dioptric distance between each refraction pairing for each eye of each subject was calculated for the total (square root of the sum of the squares of ΔM, ΔJ₀ and ΔJ₄₅) and astigmatic (square root of the sum of the squares of ΔJ₀ and ΔJ₄₅) components of the refraction. The mean total and astigmatic variability in refraction for each eye was calculated as the mean dioptric distance between all 3 comparisons. Right and left eyes were pooled and the mean total and astigmatic variability was calculated within each group.

Results: DS eyes exhibited a significantly greater mean total dioptric distance in refraction (+0.66D ± 0.67D) than control eyes (+0.20D ± 0.17D)(t=10.07, p<.001) with 96.7% of control eyes ≤ 0.50D, compared to only 59.4% of DS eyes. No control eye had mean total dioptric distance over 1.50D, whereas 8.9% of DS eyes exceeded that benchmark. When only the astigmatic component is considered, DS eyes exhibited a significantly greater mean astigmatic dioptric distance in refraction (+0.41D ± 0.40D) than control eyes (+0.13D ± 0.13D)(t=9.97, p<.001), with 98.16% of control eyes ≤ 0.50D, compared to 77.7% of DS eyes. No control eye had mean astigmatic dioptric distance over 1.27D, whereas 6.25% of DS eyes exceeded that benchmark.

Conclusions: Refractive variability with autorefraction in DS was 3.3x (total) and 3.15x (astigmatic) the levels observed in controls, indicating greater potential uncertainty in the starting point for subjective refraction for this population.