Proximal target binocular stimulation produces a loss of spatial accuracy beyond the fovea, according to research published in Investigative Ophthalmology & Visual Science. These findings confirm the existence of impairments in an eccentricity-dependent mechanism and a separation-dependent mechanism in patients with strabismus.

Researchers enrolled individuals with strabismic amblyopia (n=10) and normal- sighted control participants (n=7) in the analysis to assess stimulus separation and eccentricity on positional deficit in patients with amblyopia. The team administered a visual perception test in which participants located a stimulus on the periphery of their vision while fixating centrally. Investigators evaluated spread (the inverse of precision) and visual perception bias during the exercise.

Among patients with strabismic amblyopia, researchers noted vision was more biased and less precise in all conditions. The group difference averaged over separation was largest at 1° indicating a disproportionate central visual field loss. Spread and bias were higher at small separations at all eccentricities, and performance showed a quadratic trend against separation, according to the report.


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Among controls, researchers observed that the linear slopes of log spread were positive at all eccentricities except 7°. The linear slopes did not differ from 0 except at 7° with an overall negative trend in patients with strabismic amblyopia.

Among a subset of study participants, monocular performance was poorer in strabismic eyes compared with normal eyes at all eccentricities and separations, with the greatest difference at 1°.

“Two positional encoding mechanisms are impaired in strabismus,” according to the researchers. “The first is an eccentricity-dependent mechanism that underlies the larger foveal disruption of positional judgments. The second, a separation-dependent mechanism associated with greater disruption at small stimulus separations, shows that binocular interference from incompatible visual input extends beyond the foveal region.”

Study limitations include a small sample size. 

Reference

Hussain Z, McGraw PV. Disruption of Positional Encoding at Small Separations in the Amblyopic Periphery.Invest Ophthalmol Vis Sci. 2022;63(4):15. doi:10.1167/iovs.63.4.15