Purpose. Age-related losses of rods and ganglion cells have been previously reported. We wanted to determine if subsequent to Ihese cell losses there \vas an enlargement of areas of complete spatial summation (Ricco's area)- Based on the literature, we assumed thai Ricco's area approximates the size of the center of ganglion cell receptive fields. The areal dimensions of these receptive field centers are thought to influence the spatial tuning of individual ganglion cells and are related to the size of light adaptation pools under scotopic conditions. Methods. Using a 2 AFC procedure, scotopic increment (hresholds were determined for 50 subjects (equal numbers of males and females) ranging in age from 19 to 87 years of age. The stimuli consisted of 10-ms, 520-nm, circular test lights of varying diameters that were superimposed and concentric with a 10°, -3.29 log scotopic troland, 640-nm, circular adapting field. The test lights were imaged on the nasal retina along the horizontal meridian 6° from the fovea. Results. On average, we found a statistically significant age-related enlargement in the area of complete spatial summation under scotopic conditions. The average angular subtenses (uncorrected for the ocular MTF) of Ricco's areas for our ten youngest (x̄ =26 yrs) and ten oldest (x̄=75 yrs) observers were approximafely 49′ and 69′ arc, respectively Conclusions. A simple model involving the convolution of our apertures and agerelaled changes in the modulation transfer function of the eye suggest that the observed enlargements in Ricco's area cannot be explained solely by optical changes of the ocular media. Therefore, neural changes must be invoked to explain, in part, the changes in the size of complete spatial summation.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - 1997|
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