Abstract
Individuals with macular degeneration typically lose vision in the central region of one or both eyes. A binocular scotoma occurs when vision loss occurs at overlapping locations in both eyes, but stereopsis is impacted when the visual field in either eye is affected. Here we map the periphery with local disparity stimuli to determine how locations with functional stereopsis relate to the scotomata in the two eyes. Participants included those with monocular (N=4) or binocular (N=6) scotomata and age-matched controls (N=5) with healthy vision. We used a novel stereo-perimetry protocol to measure local stereopsis across the visual field (up to 25° eccentricity). Targets (with or without depth information) were presented on a random dot background. Depth targets had true binocular disparity of 20’ (crossed), whereas non-depth targets were defined by monocular cues such as contrast and dot density. The target was a 1° square region at the fovea and was m-scaled with eccentricity. Participants viewed the display binocularly and were asked to maintain fixation during target presentation. During the response interval, participants (i) reported the location of the target, and (ii) indicated whether it was in depth or flat. Depth sensitivity (d’) estimates from each location were then combined to generate a stereopsis map. This stereopsis map was compared to monocular microperimetry measured in a scanning laser ophthalmoscope that mapped out the functional extent of the scotoma in each eye. Across all observers, the parts of the visual field outside the union of the two eyes’ scotoma predicted regions with stereopsis, whereas the intersection (overlap) of the scotomata predicted the functional binocular vision field. This explains why individuals with non-overlapping scotomata in the two eyes may have intact binocular visual fields, but be severely compromised in tasks of daily living that benefit from stereopsis, such as eye-hand coordination and navigation.