The effect of age on the area of complete spatial summation for chromatic and achromatic stimuli

Previously, an association between the area of complete spatial summation (Ricco's area) and age under scotopic conditions had been found. The authors sought to determine whether Ricco's area is similarly associated with age under photopic achromatic and selective S-cone conditions in peripheral vision and whether any association relates to a loss of ganglion cell density as determined by measurements of peripheral grating resolution acuity.

Achromatic spatial summation functions were plotted for 68 healthy subjects (aged 20-77 years) in four oblique meridians on a gray background field of 10 cd/m(2). Similar functions were generated for the S-cone pathway (isolated using Stiles' two-color threshold method) for the same locations. Ricco's area was determined using two-phase regression analysis. Achromatic peripheral grating resolution acuity was measured at the same locations using high-contrast Gabor stimuli, as an estimate of localized functional ganglion cell density.

There was a notable decrease in overall contrast sensitivity with age for all stimulus sizes. However, there was no evidence of age-related change in Ricco's area for either achromatic (superior field, r(2) = 0.05; inferior field, r(2) = 0.0007; all P > 0.05) or chromatic (superior field, r(2) = 0.01; inferior field, r(2) = 0.006; all P > 0.05) stimuli, despite a significant decrease in peripheral grating resolution acuity with age (superior field, r(2) = 0.15; inferior field, r(2) = 0.17; both P < 0.05).

An age-related decline in functional ganglion cell density is not accompanied by a significant change in Ricco's area for achromatic or chromatic stimuli.