Sparing of coarse stereopsis in stereodeficient children with a history of amblyopia

Abstract

Stereoscopic depth perception may be obtained from small retinal disparities that can be fused for single vision (fine stereopsis), but reliable depth information is also obtained from larger disparities that produce double vision (coarse stereopsis). Here we assess the possibility that the early development of coarse stereopsis makes it resilient to the factors that cause amblyopia by comparing performance in children with a history of strabismic, anisometropic, or aniso-strabismic amblyopia and age-matched controls (5-12 years). The task was to indicate whether a cartoon character was nearer or farther away than a zero-disparity reference frame. Test disparities were grouped into fine and coarse ranges based on preliminary assessment of diplopia thresholds. In the fine range, accuracy increased with disparity for both groups, but children in the amblyopia group performed significantly worse than children in the control group, particularly when their amblyopia was associated with strabismus. In the coarse range, accuracy was constant across all disparities for both groups although performance appeared to be poorer in the aniso-strabismic group. These results suggest that, under some conditions, stereopsis for large disparities may be spared when stereopsis for small disparities is disrupted by early visual deprivation. This undetected residual binocular function has important clinical implications given recent efforts to improve amblyopia treatment outcomes by employing binocular treatment protocols.

Stereopsis and amblyopia: A mini-review

“…Some patients who are categorized as stereo-blind using standard clinical tests evidence a variety of residual stereoscopic functions, including preserved sensitivity to second-order disparity signals (McColl, Ziegler & Hess, 200; Harris et al, 2000), preserved sensitivity to motion in depth in peripheral vision (Sireteanu, Fronius, & Singer, 1981). Recent work suggests that coarse stereopsis may be selectively spared in stereo deficient children with a history of amblyopia (Giaschi et al, 2013). In the sections below we focus primarily on stereopsis measured with standard, static, clinical tests.…”

Recovering stereo vision by squashing virtual bugs in a virtual reality environment

“…Coarse stereopsis is considered to be important to extend the range of disparity sensitivity, as a guide to vergence eye movements, and as a 'back up' system for individuals with strabismus [30]. Indeed, there is recent evidence that coarse stereopsis develops much earlier than fine stereopsis [31], and that it may be relatively 'spared' in individuals with a history of amblyopia [32]. Whether the same mechanisms are capable of supporting stereoacuity better than one arc minute in strabismic patients or whether there are specialized mechanisms supporting anomalous correspondence is a matter for further research.…”

Stereo vision and strabismus

“…15,16,[54][55][56][57][58][59] Fu et al 55 suggest that the better performance on contour stereograms may be because these 'provide cues to fusion that allow some patients with strabismus to better control their deviations than random dot targets'. This motor explanation may well contribute, 58 but sensory mechanisms probably contribute as well.…”

“…This motor explanation may well contribute, 58 but sensory mechanisms probably contribute as well. Giaschi et al 56 have reported that amblyopic children with poor or no stereopsis on the Randot Preschool test nevertheless perform as well as controls when the stimulus was a monocularly visible cartoon character with a large disparity. They conclude that although the 'fine stereo' sensory system is impaired in these children, 'coarse stereo' is spared.…”