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Marianne E. Piano, Anna R. O'Connor, Anita J. Simmers; The Impact Of Degrading Binocular Single Vision Upon Fine Motor Skill Tasks. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1777.
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Diagnosis/treatment of binocular single vision (BSV) defects is part of orthoptic practice. Findings of studies attempting to quantify the contribution BSV makes to aspects of visuomotor function conflict, possibly due to individual differences in task performance and long-term adaptation to reduced/absent BSV. This study aims to address these issues via repeated measures design using participants with normal BSV. It will evaluate, within subjects, the impact of degrading BSV on performance of certain fine motor skill tasks requiring speed/accuracy.
Binocular functions (Frisby/Preschool Randot (PSR) stereoacuity, horizontal phasic prism fusion amplitudes) were measured in participants aged 18-40 years (n = 54), with Frisby stereoacuity <300"arc and logMAR visual acuity (VA) ≤0.300. Participants performed 3 timed motor tasks: water-pouring (450mLs accurately into 5 measuring cylinders at 90mL) and bead-threading on upright needles (30 large, 22 small beads). Task and binocular function measures were then repeated in randomised order while wearing convex spherical lenses of increasing power over one eye, reducing uniocular VA in 3-line increments up to 12 lines degradation, followed by a convex spherical lens of sufficient power to induce uniocular suppression. Comparisons were made with Kruskal-Wallis tests.
Median Frisby stereoacuity levels were 20" arc at baseline, reducing to 30" arc when VA was degraded by 3 lines, 55" arc by 6 lines, 215"arc by 9 lines, and was unmeasurable in most by 12 lines. Some maintained fusion/stereopsis at 12 lines degradation and required an additional lens to induce uniocular suppression, while in others it was unmeasurable at 6 or 9 lines degradation. Task performance times deteriorated for the large bead task (0-20% performance deterioration between lenses, total 43% deterioration from median baseline time of 50.38s, p = 0.029), and small bead task (0-23% performance deterioration between lenses, total 41% deterioration from median baseline time of 56.82s, p <0.001). During the water-pouring task, degrading BSV was significantly associated with altered accuracy (p = 0.025), and performance times (p < 0.001), but alterations were small (0.20-0.33s, 0.5mL) and not linearly associated with level of BSV.
Based on this sample, degrading BSV significantly affects performance in certain fine motor skill tasks, more so when suppression occurs. Findings agree with other studies showing impairment on bead-threading tasks when stereoacuity/motor fusion is impaired. The task battery is limited and further research is required to establish the contribution BSV makes to other fine motor tasks.
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