Abstract
Parafoveal or peripheral vision is known to be important for various everyday activities such as reading, visual search, or navigation. This is particularly relevant to individuals with visual-field defects. As visual-field loss appears in varying patterns and locations, it is important to assess the spatial extent of a person’s remaining vision relevant to everyday function. Using a novel method to quantify the spatial extent of functional field of view (FFV), here we assessed the effects of crowding, aging, and glaucoma on FFV. Unlike visual acuity measured by single-letter recognition or visual-perimetry measured by light sensitivity, our FFV test requires recognition of crowded letters under divided attention. FFV was measured with letter triplets presented at a given location across the visual field, spanning 36° horizontally and vertically. A subject’s task was to recognize the middle-letter in letter triplets and report whether the middle-letter was the same as the letter displayed at the central fixation region concurrently. The threshold distance (eccentricity) between the fixation and target location was adjusted via an adaptive procedure, yielding 80% recognition accuracy. Over the trials, a plot of threshold distance versus target location was constructed, resulting in a visual-field map tracing out the visible boundary. FFV was quantified as the area under the visible boundary. The results obtained from three subject groups: young (n=19) and old (n=27) normal vision, glaucoma (n=30) showed significant differences in FFV between crowded and uncrowded conditions (p < 0.001), young and old normal vision (p=0.014) and glaucoma and old normal vision (p<0.001). These results suggest a significant shrinkage of FFV due to crowding, normal aging, or ocular pathologies. We also observed a significantly smaller FFV than expected from standard visual-perimetry across all subjects (p<0.001). Our findings highlight the importance of assessing functionally relevant visual-field to better understand a person’s everyday visual function.