PURPOSE

Binocular summation for contrast detection in the fovea is lower in older normal subjects. At present, no binocular summation data exist for contrast detection in older subjects in the peripheral field.

METHODS

Monocular and binocular contrast thresholds were measured for sine-wave gratings of 1 c/deg (F1) and 4 c/deg (F4) in the fovea in young and older visually normal subjects. Measurements were also obtained at 8 degrees in the superior field for gratings of 1 c/deg (P1) and 4 c/deg (P4).

RESULTS

Binocular summation ratios in young subjects at the fovea and periphery were not statistically different at either spatial frequency. In older subjects, analysis of the relevant conditions showed significantly lower summation ratios for: P4/F4 combination (p = 0.05), and P4/P1 combination (p = 0.03). No significant differences existed for F1/P1 and F1/F4 combinations (p > 0.05).

CONCLUSIONS

Lowest binocular summation ratio is shown with older subjects for gratings of 4 c/deg in the periphery (P4). Further analysis suggests the possibility that this is due to a larger relative loss in binocular sensitivity. Data are discussed in terms of selective loss of binocular neurons mediating peripheral sensitivity in the ageing eye.