Zoom Brown Bag: Modeling the impairment of smooth pursuit eye movements in macular degeneration

Abstract:
Age-related macular degeneration (AMD) is the most prevalent cause of central visual field loss. Since the fovea (oculomotor locus) is often impaired, individuals with AMD typically have difficulties with saccadic and smooth pursuit eye movements (Verghese, Vullings, & Shanidze, 2021). We propose that smooth pursuit eye movements are impaired in macular degeneration due to two factors: 1) the transient disappearance of the target into the scotoma and 2) noise that depends on the eccentricity of the oculomotor locus from the target. To assess this claim, we measured performance in a perceptual baseball task where observers had to determine whether a target would cross or miss a rectangular region (plate) after being extinguished (Kim, Badler, & Heinen, 2005), when instructed to either fixate a marker or smoothly track the target. We recorded eye movements of 4 AMD eyes and 6 control eyes with simulated scotomata (matching those of individual AMD participants) during the task. We found that controls with simulated scotomata could better discriminate strikes from balls compared to AMD participants, particularly in the smooth pursuit condition. We also developed a model that predicted performance on the task using visible portions of the target trajectory given the scotoma and position uncertainty given the eccentricity of the eye from the target. The model showed a similar trend to participant results, with better discrimination for simulations using control eye position data (foveal oculomotor locus) than for MD data (peripheral oculomotor loci). However, the model's discrimination performance was largely better than actual participant performance. These findings suggest that while the disappearance of the target due to the scotoma and noise due to the eccentricity of the peripheral oculomotor locus from the target in AMD affect perceptual discrimination, these factors account only partially for the impairments. https://www.ski.org/users/jason-rubinstein

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