Clinical assessment of contrast sensitivity

Abstract

Visual system transfers information at both high and low contrastlevels. It has been customary to assess visual function by measuring visual acuity although it has been well documented for over ten years' time that measurement of contrast sensitivity may reveal loss of visual function that is not detected by measurement of visual acuity.There are several commercially available clinical tests that are used in Scandinavian countries for assessment of visual transfer function in low contrast domain. We have chosen six of them for comparison: Cambridge Low Contrast Gratings, Vistech's contrast sensitivity tests for distance and near, PelliåRobson's low contrast letter chart, Vistest's LH‐5 contrast visual acuity test, and Mentor's computer based device for measurement of both contrast sensitivity and low contrast visual acuity.Each of the commercial tests measures low contrast vision in slightly different way. In order to have an overview of the function of these tests we have assessed vision of visually impaired patients and normally sighted subjects using all tests during one visit. In general the grating tests result inslightly higher contrast sensitivity values than the optotype tests. Contrast sensitivity values measured with grating tests are difficult to assess because the size of the stimulus affects the values.Based on our results, we recommend assessment of low contrast visual transfer using an optotype test as the basic test and a grating test in order to assess vision for orientation and mobility. The grating test should be used at two different distances resulting in approximately two and ten degree stimuli.