The Impact of Induced Optical Blur on Monocular and Binocular Depth-Related Visuomotor Task Performance

The purpose of this study was to determine the impact of induced optical blur on a 3D task that probes complex visuomotor performance capabilities of humans.

Fifteen visually normal, cyclopleged adults (mean ± 1 SD = 23 ± 2.6 years) guided a metal loop along a wire convoluted in depth without making contact, while being video recorded for analysis. The task was performed binocularly and monocularly, without blur, and with two magnitudes of induced spherical and astigmatic blur of equal strengths (2.25 diopters [D] and 6.25 D). Blur patterns were induced before both eyes (isometropia) or before only one eye (anisometropia). For isometropic astigmatism, blur was also induced with parallel and orthogonal axes in both eyes. The buzz-wire patterns, viewing condition, and induced blur were all randomized across participants.

Binocular error rate (number of loop-to-wire contacts per second) and error duration (percentage of time spent making errors) increased at high blur strength (P < 0.001), more so for astigmatism than spherical power (p < 0.001) and more so for isometropic than anisometropic viewing (P = 0.02). Low astigmatism with orthogonal axes bilaterally produced higher error rate and error duration than astigmatism with parallel axes bilaterally (P < 0.001). Only error duration increased with high blur for monocular viewing (P ≤ 0.004). Task speed remained invariant across test conditions. Multiple repetitions did not impact task performance.

The deterioration of depth-related visuomotor task performance with optical blur depends on its magnitude, radial symmetry and the similarity between the two eyes. Performance drop is largely from spending more time making/correcting errors, whereas the overall speed remained undiminished.