Binocular summation in the fovea and peripheral field of anisometropic amblyopes

Purpose. Binocular performance in the central and peripheral visual fields was compared for normal and anisometropic amblyopes. Methods. Binocular and monocular thresholds to a light detection task were measured along the four principal meridia in 10 young normal subjects and 10 anisometropic amblyopes using the Humphrey's Visual Field Analyser. Thresholds were obtained at the fovea and at retinal eccentricities of 5 degrees, 10 degrees, 15 degrees, 25 degrees, 40 degrees and 55 degrees on the horizontal, vertical and oblique meridia of 45 degrees and 135 degrees. Results. Binocular summation ratios (binocular sensitivity/'best' monocular sensitivity) were calculated for all the eccentricities. In the normal group, the mean binocular summation ratio for the fovea and the peripheral field was not significantly different. In the amblyopic group, subjects showed no or minimal binocular summation in the foveal region but reached normal ratios in the periphery. Discussion. Results are discussed in terms of tolerance to interocular sensitivity differences in the periphery and selective losses in cortical cells.