Purchase this article with an account.
L.A. Schmidt, P.M. Pearson, N. Ly, W.H. Swanson; Ganglion Cell Loss: Cortical Pooling Analysis of Aging Effects for Chromatic and Achromatic Stimuli . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3287.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose:To analyze effects of normal aging on visual sensitivity in terms of heterogeneous ganglion cell loss using our cortical pooling model of glaucomatous visual defects. Methods:Contrast sensitivity on an equal–energy white background was measured in normal subjects for modulations along the three cardinal axes in colour space: luminance, red–green and tritan. Thresholds for both small (0.6º) and large (3º) stimuli were evaluated in 19 younger (M=22.7± 3.4 years) and 15 older (M=70.2±7.8 years) viewers at 12º eccentricity in each quadrant of the visual field. Results:The cortical pooling model of glaucoma suggests that differential sensitivity to ganglion cell loss evidenced by perimetric tests is a consequence of the size of the spatial filters that pool the responses of the ganglion cells rather than a consequence of some property of the ganglion cells themselves. The model predicts that the effect of age should be greater for small than for large spots when the stimuli are mediated by small spatial filters but not when they are mediated by larger spatial filters. Consistent with larger spatial filters in the chromatic pathway than in the achromatic pathway, chromatic sensitivity was influenced by the size of the stimulus more than achromatic sensitivity (red–green: t(37)=8.23, p<.001; tritan: t(33)=11.01, p<.0001). For the chromatic stimuli, the size of the stimulus did not influence the loss in sensitivity with age (red–green, t(17)=0.48, p=.639; tritan, t(14)=0.82, p=.426). In contrast, the size of the stimulus did significantly influence the loss of achromatic sensitivity with age (t(18)=3.63, p=.002). Loss of sensitivity with age was greatest for the tritan stimuli (vs red–green: t(14)=3.65, p=.003; vs luminance: t(14)=2.68, p=0.018) while that for the red–green stimulus was not significantly different from that for luminance stimulus (t(18)=0.70, p>.05). The cortical pooling model also suggests that the variability of achromatic thresholds obtained using large stimuli should be smaller than the variability when small stimuli are used. Consistent with these predictions, decreasing stimulus size increased variability within the visual field for achromatic stimuli (t(37)=3.99, p<0.001). Conclusions:The results are consistent with predictions of the cortical pooling model for effects of heterogeneous ganglion cell damage.
This PDF is available to Subscribers Only