PURPOSE. Age-related macular degeneration (ARMD) induces a decrease in visual functions. This study assess binocular summation for static and drifting stimuli in older observers with and without ARMD. METHOD. Twenty older subjects with aged-related macular degeneration (62-77 yrs) and twelve older observers without ocular pathologies (61-74 yrs) were tested. Stimuli were presented on a computer monitor with a mean luminance of 9,5 cd/m2. Refraction was corrected for all observers for a viewing distance of 57 cm. A sine wave grating of 0,5 cpd was presented at fixation (central) in a hard-edged square patch subtending 10x10 degrees. Static (0 Hz) and dynamic (16 Hz) conditions were tested. Observers had to discriminate the orientation (vertical or horizontal) of the grating for the static condition. For the dynamic condition, subjects were instructed to discriminate the direction of motion (right or left) for a vertical grating. Each of the conditions were evaluated monocularly and binocularly. Contrast thresholds (75% correct) were measured with a two alternative forced choice procedure using the PEST method.
RESULTS. All observers in the group without ocular pathologies showed binocular summation for all conditions, but summation was less important in the dynamic condition. For the ARMD observers, one third showed binocular inhibition and the others presented either binocular summation or suppression for the static condition. Globally, for the dynamic condition, the ARMD group showed less binocular summation or inhibition.
CONCLUSIONS. Some ARMD subjects show a pattern of binocular summation similar to that of older observers without ocular pathologies, wheraes others show binocular inhibition. This suggests changes in the cortical integration of binocular information. ARMD inhibitors may thus be better using only one eye for some day-to-day activities involving low spatio-temporal frequency information.