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T. Redmond, M. B. Zlatkova, D. F. Garway-Heath, R. S. Anderson; The Effect of Age on the Area of Complete Spatial Summation for Chromatic and Achromatic Stimuli. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5846.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have reported an age-related increase in the area of complete spatial summation (Ricco’s Area) under scotopic conditions (Schefrin et al, 1998; based on a sample of 50 healthy observers), interpreted as increased convergence from photoreceptors in compensation for an age-related loss of retinal neurons. We wished to investigate if the same holds true under photopic conditions for both achromatic stimuli and chromatic stimuli targeting the S-cone pathway. In addition we wanted to determine how any change might relate to ganglion cell loss as determined by measures of peripheral grating resolution.
Spatial summation curves were measured at 10 deg eccentricity for 57 subjects between the ages 20-69 years using both white-on-white increment stimuli and blue stimuli superimposed on an intense yellow adapting background (Stiles two-color threshold method). Ricco’s area was determined using piecewise regression analysis. Achromatic resolution acuity (grating orientation discrimination) was also measured at the same peripheral locations as an indicator of retinal ganglion cell sampling density loss with age in the same subjects.
Results indicate that, while there is a notable increase in threshold for both achromatic and S-cone stimuli with age, there is no significant change in Ricco’s area for either stimulus type (one way ANOVA: p>0.3 (achromatic), p>0.5 (chromatic)). The average size of Ricco’s area for achromatic stimuli in the youngest and oldest age decades was 0.079deg2 and 0.071deg2 respectively and for chromatic stimuli, the mean size of Ricco’s area was 0.39deg2 for the youngest decade and 0.49deg2 for the oldest decade. A significant decrease in resolution acuity, and hence ganglion cell sampling density, was found as a function of age (one-way ANOVA: p<0.01). Resolution acuity remained constant until approximately 40 years of age and declined at an average rate of -0.6dB per decade thereafter.
While retinal ganglion cell density declines with age, this is not accompanied by a change in the area of complete spatial summation for either achromatic or s-cone stimuli. These results do not support the hypothesis of a change in the area of complete spatial summation as a compensation mechanism for the loss of retinal ganglion cells under photopic conditions.
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