Contribution of binocular visual function and its impairment by Bangerter foils to the performance of a precision reaching, grasping and placing task in healthy adults

Pilar Granados-Delgado¹Miriam Casares-López¹José J Castro-Torres¹Xiaoxin Chen²Ewa Niechwiej-Szwedo^2*

• ¹Universidad de Granada, Granada, Spain
• ²University of Waterloo, Waterloo, Canada

Upper limb movement execution is affected in patients with vision impairments resulting from ocular pathologies or binocular anomalies. Deficits in motor performance have been correlated with reduced contrast sensitivity, phoria, and stereoacuity. This study evaluated the effects of increased straylight induced by Bangerter foils on binocular visual function and examined the impact on eye-hand kinematics during a high precision reaching, grasping and placement task (i.e., bead threading). Twenty-one healthy participants, 21-41 years old, participated in the study. Visual function assessment included visual acuity (VA), contrast sensitivity (CS), stereoacuity (SA), phoria, and fusional vergences (FV). Vision was impaired experimentally using Bangerter foils 0.4. Participants performed a bead threading task under three randomized viewing conditions: binocular baseline (BB; normal vision), binocular viewing with a foil over the dominant eye (FDE), and foils over both eyes (FBE). Eye and hand movements were recorded using an eye tracker and a motion capture camera. Visual functions (VA, CS, and stereoacuity) were impaired when viewing with the Bangerter foils. Pairwise comparison between viewing conditions confirmed statistically significant differences between BB, FDE and FBE for mid to high spatial frequencies (6, 12 and 18 cycles per degree; p < 0.05). Break points for positive and negative fusional reserves were impaired when interocular differences increased (i.e., FDE condition). The impairment did not have any impact on phoria. Results from the kinematic analysis revealed threading duration was prolonged using Bangerter foils on both eyes (FBE condition). In contrast to the hypothesis, visual deficit due to foils did not affect any other kinematic measures. However, results from mixed model analyses revealed that individual differences in phoria and fusional vergence had the most significant influence on reaching performance. Specifically, a larger exophoria magnitude was associated with longer reach duration, lower peak velocity and prolonged total time to complete the task (p < 0.05). Inducing short-term deterioration through the alteration of contrast sensitivity at high spatial frequencies without a clinical deterioration in stereopsis does not have a significant impact on precision grasping and placing movements, in a repetitive manual task. Notably, this study demonstrated that phoria impacts the execution of reaching movements.