Abstract
Macular degeneration (MD) affects the central portion of the retina, resulting in a scotoma. When the scotoma is binocular, it can obscure objects of interest. Furthermore, individuals with MD are often unaware of the scotoma location and of the information they are missing, causing further difficulties in tasks of daily living. As scotoma maps are typically monocular, we address the challenge of precisely mapping the binocular scotoma using an eye-tracker.
Nine individuals with MD (six with binocular scotomas) and 3 age-matched controls participated in our study. We measured the extent of the monocular scotoma in each eye using a Scanning Laser Ophthalmoscope/Optical Coherence Tomography (SLO/OCT). Previously, Ghahghaei and Walker (2016) proposed a way to estimate the binocular scotoma by aligning the individual monocular maps on the foveae. We determined whether this algorithm approximates the true scotoma measured under binocular viewing, while eye position was monitored with an eye-tracker. Participants fixated a cross and responded whenever they detected a briefly flashed dot. The dots were first presented on a coarse grid, and then at manually selected points to refine the shape and edges of the scotoma.
The monocular scotoma measured in the SLO and eye-tracker are identical, suggesting that individuals use the same preferred retinal locus under both imaging conditions. Moreover, all participants used clustered fixation loci corresponding to their preferred fixation locus. Critically, the binocular scotoma maps from the eye-tracker were highly similar to those obtained with the Ghahghaei-Walker algorithm, yielding an effective method to assess residual retinal function in binocular vision.
Determining the size and location of the binocular scotoma with respect to the fixation locus is key to effective training of oculomotor strategies in MD. Our eye-tracker method offers a reliable and sensitive tool for measuring both monocular and binocular scotomata, without the need of an SLO/OCT.