Abstract
Aim: It has been shown that, in the central field, binocular performance for contrast detection tasks decreases in visually normal older subjects compared to young subjects. Although binocular summation in the peripheral field of older subjects has been investigated with respect to a light detection task, no data exist on contrast thresholds to sinusoidal gratings. Methods: Contrast thresholds in young and older visually normal subjects were measured to sine-wave gratings of 1 and 4 c/deg in the fovea and at 10 degrees in the superior field. Monocular and binocular contrast thresholds were obtained with the subjects optimally corrected for both distance and retinal viewing position. Results: Although contrast thresholds were lower in the periphery than in the fovea, binocular summation ratios in the young subjects showed no significant differences (p>0.05) in the fovea and at 10 degrees in the superior field, at either spatial frequencies. The older subjects showed higher binocular summation ratios to spatial frequency of 4 c/deg compared to 1 c/deg both in the fovea and in the periphery (p<0.05). Conclusions: A decrease in binocular summation is shown with the middle spatial frequency compared to the lower spatial frequency at both the central and peripheral retinal fields in older subjects. Possible reasons for this and the clinical implications are discussed.