SPATIAL SUMMATION OF THE DIFFERENTIAL LIGHT THRESHOLD AS A FUNCTION OF VISUAL-FIELD LOCATION AND AGE

Static differential light thresholds were measured as a function of st imulus size (Goldmann sizes I-V) along four visual field meridia (75, 165, 255 and 345 degrees) with the Humphrey Field Analyzer 640. Data w ere obtained for both young (n = 10, age 23.6 +/- 2.9 years) and elder ly (n = 10, age 72.0 +/- 5.2 years) normal subjects. The resulting per ipheral spatial summation curves could be equated to the foveal data s imply by a change in size scale, which increased linearly with eccentr icity. E(2) values, expressing the eccentricity at which stimulus size must double for performance to remain comparable to the fovea, were i n the order of 3-9 degrees. Whilst the rate of scale change is approxi mately the same for both young and elderly observers, differences in p erformance can be explained by a combination of lower sensitivity and a bias in sensitivity towards larger stimulus sizes with increasing ag e.