Reflex maintenance of vergence eye alignment to small natural images is at risk for adults and young children

ABSTRACT Purpose Typical human adults make reflex eye movements and computations to support stable binocular vision in milliseconds. The current project was designed to determine the impact of visual field extent on reflex vergence performance of adults and six‐ to eight‐year‐old children for images of natural scenes. Methods Twenty‐two typical adults (23–55 years) and 12 typical six‐ to eight‐year‐old children were presented with dichoptic natural scenes in continuous tracking and step disparity formats while vergence realignment responses were recorded. The images had radii varying from 1° to 16° and either moved smoothly at random disparity velocities (≥30 s) or stepped in disparity to 0–6° in 1.5 s trials. Results Peak correlations and latencies between stimulus and vergence velocities were computed for continuous tracking trials, and response amplitudes after 1.25 s were computed for step trials. Continuous tracking responses of both adults and children were unaffected by reductions in image radii from 16° to 3°, but their vergence response amplitudes to step changes and the range of disparities over which a stimulus‐driven response was generated decreased with decrease in stimulus radius. The participants moved to their dissociated heterophoria position for disparity stimuli that exceeded their reflex vergence response range for these limited duration stimuli. Conclusions Patients with peripheral visual field loss needing to align their eyes to a new depth plane and patients provided with virtual binocular images in clinical therapy or assistive devices must use disparity over a limited field extent to realign their eyes. Performance to natural image content here suggests that reflex maintenance of eye alignment is at risk for moderate disparities when the stimulus radius falls below approximately eight degrees. This is of particular concern for patients with limited binocular function resulting from amblyopia or strabismus, for example.