Evidence against age-related enlargements of ganglion cell receptive field centers under scotopic conditions.

Age-related changes in the neural organization of spatial information are required to account for much of the senescent loss in human scotopic spatial vision, specifically declines in the high spatial frequency cut-off of the contrast sensitivity function and enlargements of the area over which there is complete spatial summation (Ricco's area). These results are consistent with hypothesized enlargements of ganglion cell receptive field centers during adulthood. This hypothesis was tested with 50 subjects (19-88 years) by measuring contrast thresholds for two low spatial frequency gratings (0.3 and 1.2 cycles per degree) at a series of scotopic mean illuminance levels. Contrast sensitivity increased with retinal illuminance and then reached a plateau, corresponding to the onset of Weber-like behavior. No age-related change in the light level associated with the onset of Weber-like behavior was found at either spatial frequency. This result is inconsistent with proposed age-related enlargements of ganglion cell receptive field centers under scotopic conditions.