Abstract
PURPOSE: Parafoveal or peripheral vision is important for various everyday activities. This is particularly relevant to those who suffer from visual field defects. Here we quantified the effect of visual crowding, normal aging, and glaucoma on the spatial extent of the functional field of view (FFV) under divided attention. METHODS: Unlike visual acuity measured by single-letter recognition or visual perimetry measured by light spot detection, we measured the FFV using a target letter presented either alone or in letter triplets appearing across the visual field. A subject's task was to report whether the target letter was the same as the letter displayed concurrently at the central fixation region (i.e., divided attention task). Over the trials, a plot of the proportion correct for letter recognition versus target location was constructed, resulting in a visual field map. RESULTS: The results obtained from three subject groups-normal young adults, normal older adults, and patients with glaucoma-showed that on average the central 20° visual field was relatively robust to uncrowded target recognition under divided attention. However, the FFV shrunk down to the central 10° visual field when the target appeared in clutter, suggesting a strong crowding effect on FFV. An additional shrinkage of the FFV occurred in the presence of aging and glaucoma. CONCLUSIONS: Using a quantitative method, we demonstrate that crowding, aging, and glaucoma independently decrease the spatial extent of FFV under divided attention and that crowding seems to be the major contributor limiting FFV. TRANSLATIONAL RELEVANCE: Our FFV test may complement standard clinical measurements by providing functionally relevant visual field information.