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Mixed Contrast Reading Card Shows Aspect of Contrast Processing That Is Independent of Detail Processing

Smith–Kettlewell Eye Res Inst, Novato, CA

Commercial Relationships: A. Colenbrander, None.

Support: None.

Abstract

Background: The Mixed Contrast reading card with alternate lines of high and low (10%) contrast, provides a simple screening test for routine clinical use to detect contrast sensitivity (CS) deficits. The black lines (HC) replace traditional reading tests. The gray lines (LC) add a measure of contrast sensitivity. It was shown (ARVO 2004/4352) that the LC threshold is correlated to the Pelli–Robson score and that the HC–LC difference is independent of ETDRS acuity.

Purpose: To further evaluate MC–card findings in general clinics and Low Vision services.

Methods:After pooling, subjects were split into four groups: 1. Subjects with > 20/40 letter chart acuity, presumably with minimal pathology: (1A): age 12–65, (1B): age 66–99. 2. Subjects with < 20/40 letter chart acuity, presumably with some pathology: (2A): retinal disorders, (2B): other disorders (opacities, glaucoma, optic nerve disease).

Results: To date, over 300 test results were analyzed. Analysis by source showed that in one busy clinic reading acuities (vs. letter chart acuity) were consistently lower than in the other settings, presumably since no special reading refraction was performed. Yet the pattern of results was the same as elsewhere.

The HC–LC differences were plotted against letter chart acuity. In all groups the HC–LC values were independent of letter chart acuity (range 20/1600 to 20/16). The results for (1A) (n=111) and (1B) (n=118) were identical, i.e. no age effect; the median difference was 1 line (range: 0–5 lines). For (2A) (n=64) the median was 4 lines (main range 2–6 lines with outliers to 13 lines). For (2B) (n=35) the median was 3 lines (main range 1–5 lines with outliers to 13 lines).

Conclusions: The MC–card readily demonstrates the presence of contrast sensitivity (CS) deficits. Unlike LC visual acuity, which shows a correlation with HC visual acuity, the HC–LC difference appears to describe a contrast parameter which is independent of letter chart acuity and, in healthy eyes, does not change with age. The common finding that CS measures tend to decline with age may, in part, reflect their correlation with visual acuity and the fact that pathology is more common in older groups.

Like visual acuity, CS deficits are not disease specific. Yet, routine detection of CS deficits is important (a) to follow progression or regression of diseases, (b) to counsel subjects about its consequences, e.g. in night driving and in various ADLs and (c) to gain familiarity with its clinical interpretation. Since the test is based on reading, it tests a larger peri–foveal (or peri–PRL) area than letter–based tests and can be used to replace conventional reading tests.

Keywords: contrast sensitivity • reading • visual acuity

© 2005, The Association for Research in Vision and Ophthalmology, Inc., all rights reserved. For permission to reproduce any part of this abstract, contact the ARVO Office at arvo{at}arvo.org.