Binocular versus monocular viewing in patients with age-related macular degeneration

Abstract

This paper compares monocular versus binocular viewing in AMD patients during fixation and the potential of binocular function. Twenty-seven patients with bilateral AMD were recruited. A scanning laser ophthalmoscope was used to identify PRLs and map retinal scotomas monocularly. An infrared eye tracker was used to evaluate gaze position changes (and indirectly retinal locus changes) between monocular and binocular fixation. Through their combined use the retinal loci used for fixation under binocular viewing conditions were identified. Binocular function was tested with Bagolini striated glasses and fusion at the PRLs was tested with a computer-driven display. It was found that only five patients used the same PRL to fixate under monocular and binocular conditions for both eyes. 44.4% of the patients with symmetrical scotomas but only one patient with asymmetrical scotomas showed no shift in gaze position. However, there was no difference between them (chi-square, p=0.03). Binocular PRLs fell on retinal areas that could be fused in 85.1% of the patients. Still, in 25.9% of the patients binocular PRLs fell within the scotoma in the worse eye. All patients exhibited fusion when tested with the Bagolini glasses, but only 33% showed evidence of fusion near the PRL. These results demonstrate that AMD patients could use a different PRL when viewing binocularly versus monocularly. Although retinal correspondence of binocularly used fixation locus is retained, fusion near the PRL seems impaired in the majority of the cases. These results provide an insight into how people with bilateral scotomas operate in the real world.