The impact of optical factors on resolution acuity in children with Down syndrome

Down syndrome (DS) is associated with reduced visual acuity that cannot be explained by motivational or attentional factors. To isolate the contribution of optical factors to visual performance in DS, two types of resolution acuity were measured: grating resolution acuity, which is limited by optical quality, and interferometric acuity, which effectively bypasses the optics of the eye.

Twenty-nine children with DS (age range, 9-16 years) were tested. Sixty-eight age-matched, developmentally healthy children acted as controls. All wore best refractive correction, and none had clinically significant ocular disease. Grating resolution and interferometric acuity were measured according to a two-alternative, forced-choice procedure.

There was no change in grating resolution acuity or interferometric acuity with age in either group. Mean grating resolution acuities were -0.12 log of the minimum angle of resolution (logMAR; SD +/- 0.07) for the control group and +0.48 logMAR (SD +/- 0.09) for the DS group. Mean interferometric acuities were -0.11 logMAR (SD +/- 0.08) for the control group and +0.004 (SD +/- 0.06) for the DS group. In the DS group, the mean interferometric acuity was reduced by a factor of 1.3, whereas mean grating resolution acuity was substantially reduced, by a factor of 4.1, compared with controls.

Grating resolution and interferometric thresholds are reduced in children with DS. However the discrepancy between developmentally healthy children and those with DS is greater for grating resolution acuity, suggesting that degradation in optical quality is a major contributor to poor visual performance in children with DS.