Improving the Reliability of the Pelli-Robson Contrast Sensitivity Test

Abstract

The clinical applications of contrast sensitivity testing have been discussed in numerous reports, and a number of printed contrast sensitivity tests are commercially available. Some of these tests use letters as targets rather than sine or square wave gratings (Regan and Neima, 1983; Pelli et al., 1988). Letter contrast sensitivity charts have the advantage of being quick to administer and the nature of the task is familiar to both the patient and the practitioner. The letter identification task has the advantage of being a multiple-alternative forced-choice procedure that limits patient criterion effects (Vaegen and Halliday, 1983). The Pelli-Robson chart (Pelli et al., 1988) consists of sixteen triplets of letters, with each letter subtending 3 degrees at the recommended viewing distance of 1 meter. Within each triplet the letters have the same contrast and the contrast in each successive triplet decreases by a factor of 0.15 log units (√2). Pelli et al. recommend scoring contrast sensitivity as the lowest contrast level at which at least two of the triplet are identified correctly.