The effect of degrading binocular single vision on fine visuomotor skill task performance.

PURPOSE To evaluate the impact of degrading binocular single vision (BSV) on performance of fine visuomotor skill tasks requiring speed/accuracy. METHODS Binocular functions (Frisby/Preschool Randot [PSR] stereoacuity, horizontal phasic prism fusion amplitudes) were measured in visually normal participants aged 18 to 40 years (n = 80). Participants performed 2-timed visuomotor tasks: water pouring (450 mL accurately into five measuring cylinders at 90 mL) and bead threading on upright needles (30 large, 22 small beads, creating two difficulty levels). Task and binocular function measures were repeated in a randomized order with monocular visual acuity (VA) reduced in three-line increments using convex spherical lenses. Analyses used were Kruskal-Wallis/Mann-Whitney U tests and linear mixed modeling. RESULTS Median Frisby stereoacuity levels were 20″ arc at baseline, 55″ arc when VA was degraded by 6 lines, 210″ arc by 9 lines, and unmeasurable by 12 lines (9 lines in some individuals). Task performance times deteriorated for the large bead task (7%-10% between lenses, total 37% from median baseline time of 51 seconds, P < 0.001), and small bead task (0.5%-15% between lenses, total 42% from median baseline time of 57 seconds, P < 0.001). Binocular function measures causing significant fixed effects were base-out fusional amplitudes in both bead tasks (large: P = 0.010, small: P = 0.011) and PSR stereoacuity in the small bead task (P = 0.047). Water-pouring task performance was not significantly affected by changes in any experimental parameter. CONCLUSIONS Degrading motor fusion as well as stereoacuity significantly affects performance in certain fine visuomotor tasks. This impact is differentially affected by task difficulty.