PURPOSE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.