Investigating Gaze Orientation and Spatial Localization in Strabismus

Purpose: Disruption of binocular vision during the critical period of development results in strabismus in 3-5% of the population. The visual system adapts to this decorrelation with the help of suppressive mechanisms that influence eye choice behavior. The overall goal of this research was to identify visual and non-visual factors that may impact gaze orientation and localization behavior in strabismus. These studies shed light on the mechanisms underlying binocular vision and spatial localization and provide insights into the temporal dynamics of visual suppression and its impact on eye-choice behavior.

Methods: In Aim 1, development of horizontal and vertical ocular alignment was assessed in six prism-reared infant monkeys using Hirschberg photographic methods. In Aim 2, ten human subjects with normal ocular alignment localized briefly presented targets, presented to same or alternate eyes under dichoptic conditions, in an unreferenced environment. In Aim 3, eye movements were recorded in two adult exotropic monkeys while performing memory saccade tasks with variable delays to assess influence on persistence of visual information on fixation-preference.

Results: Aim 1: Monkeys reared with prisms during infancy developed strabismus as early as 3 weeks of age (~3 months in humans) suggesting influence of both visual and non-visual mechanisms in development of normal alignment. Aim 2: Under conditions of binocular competition (dichoptic viewing), human subjects were unable to compensate for their inherent phoria and made greater errors as compared to same-eye viewing condition. Aim 3: Fixation preference behavior was observed in adult prism-reared monkeys during memory-guided saccades, similar to patterns observed during visually-guided saccades. Memory delays up to 800msec did not alter fixation preference behavior.

Conclusion: Prism-reared monkeys mimic strabismus in humans and are a useful model to study its behavioral and neurophysiological implications including influence of oculomotor proprioception. Binocular dissociation in absence of visual cues, leads to inaccurate localization even in normal ocular alignment, indicating that extra-retinal eye position feedback in the form of oculomotor proprioception may be imprecise or derived from the wrong eye. Visual suppression in strabismus leads to long-lasting adaptations that influence eye choice behavior beyond the stimulus presentation time (800ms), as indicated by fixation patterns of localization.