Reliability and validity of simple photographic plate tests of contrast sensitivity

Abstract

Sets of edge and square wave grating photographic plates of varying contrasts were used to measure the mid to low spatial frequency range of the contrast sensitivity function (CSF) of 20 subjects with evident ocular disease and 20 age-matched normal subjects. Both plate tests were shown to have good test-retest reliability and to correlate well with electronic cathode ray tube (CRT) measures of CSF. The edge test, when administered in 2-dB steps of ascending contrast, has optimum sensitivity of 0.70 and specificity of 0.84 for detecting the patient with ocular disease with a fail criterion of less than 38 dB. A measure of edge contrast sensitivity was also shown to be a good predictor of the peak of the CSF, which is shown to be largely independent of the visual acuity of the subject. The 2 c/deg and 4 c/deg plates did not provide more information about the visual difficulties of subjects than the edge test. We advocate the use of an edge test as a simple clinical measure of low spatial frequency contrast sensitivity that provides information about visual dysfunction not provided by a measure of visual acuity.