Depth-Related Visuomotor Performance in Keratoconus and Its Relationship to Stereopsis

The purposes of this study were to quantify the impact of degraded binocularity in keratoconus and its improvement with rigid contact lenses on a depth-related visuomotor task that emulates complex activities in daily living; and to determine whether visuomotor performance may be predicted from psychophysical estimates of stereo threshold.

Participants were instructed to pass a metal loop around a wire convoluted in depth. Error rate and speed were measured in 26 controls, 30 cases with keratoconus with best-corrected spectacles, a subset of 17 cases with rigid contact lenses, and 10 uncorrected myopes with acuity and stereo thresholds comparable to the keratoconic cohort. Stereo thresholds were determined using random-dot stimuli.

Binocular error rates were lower than monocular error rates for controls, uncorrected myopes, and the better-performing half of cases (p < 0.001, for each), but not for the worst-performing half (p = 0.07). Error rates in cases improved with contact lenses (p < 0.001). Within each cohort, the error rate was poorly correlated with the stereo threshold (r2 < 0.12, for each). Monocular speeds were significantly lower than binocular speeds for controls than for cases (p = 0.003) and for uncorrected myopes than cases (p = 0.001).

Degraded binocularity in keratoconus may limit the ability to perform depth-related visuomotor tasks. A portion of this loss may be overcome by using rigid contact lenses. The attributes of visuomotor task performance are, however, not predictable from the psychophysical estimates of stereo thresholds.