Supra–Threshold Contrast Matching With Aging and in Age–Related Maculopathy

Abstract

Abstract: : Purpose: This study has two goals. One goal is to study supra–threshold contrast perception in a wider group of subjects than has been previously studied and with respect to age. The other goal is to examine supra–threshold contrast perception in age–related maculopathy (ARM) and age–related macular degeneration (AMD). Methods: Two control groups (twenty subjects) with normal vision aged 20–49 and 50–80 and a third group (four subjects) with ARM aged >50 participated. In the ARM group, one subject had early atrophic ARM, 2 subjects had geographic AMD and one had exudative AMD. Contrast sensitivity (CS) up to 8 cycles per degree and supra–threshold contrast matching were measured. In the case of subjects with ARM, CS was measured to the highest spatial frequency that they could detect. CS was measured with a temporal 2AFC staircase procedure. A method of limits was used for contrast matching. A 0.5 cycle per degree sine–wave grating was the standard grating, the subject being asked to match the contrast of a test grating of a different spatial frequency. Results: In the groups with normal vision, contrast sensitivity and supra–threshold contrast matching up to 8 cycles per degree did not vary with age (repeated measures ANOVA, p>0.05 for both). There was a significant difference in CS between the older normal group and the ARM group, even for subject HN who still had good visual acuity, despite early ARM. All subjects with ARM, including those with more advanced acuity and CS loss, showed the presence of contrast constancy, as evidenced by flattening of the contrast matching curves with increasing contrast. For example, for matches between 0.5 and 1 cpd at 60% contrast, the ratio of contrast matches for all four subjects with ARM was within the 95% of normal range, even when the ratio of contrast sensitivity was outside the 95% range. Conclusions: The visual system incorporates a "gain" so that contrasts above threshold are perceived more accurately than near threshold. Our data supports the work of Georgeson and Sullivan (1975), but extends their data to show that contrast constancy exists in a larger group of naïve subjects of different ages. In ARM, there appears to be modification of the gain, to compensate for considerable contrast sensitivity losses.

Keywords: low vision • contrast sensitivity • aging: visual performance