Brightness sensitivity and color perception as predictors of relative afferent pupillary defect

PURPOSE. To characterize the relationship between brightness sensitivity and color perception and relative afferent pupillary defect (RAPD) in patients with optic neuropathy. METHODS. The "swinging flashlight test" was used to diagnose RAPD, the degree of which was quantified by neutral density filters, in 325 consecutive patients in a case- control study. A separate examiner, masked to the pupillary findings, then assessed participants for Ishihara color plate reading, brightness sense, and red perception. The latter two were quantified by asking the patient to score (out of 100%) brightness (of a light source) or redness (of an object) of the two eyes relative to each other. Pearson correlation coefficients and receiver operating characteristic (ROC) curves were calculated. RESULTS. Brightness sense (r = -0.79; 95% confidence interval [CI], -0.84 to -0.73; P < 0.0001), red perception (r = -0.73; 95% CI, -0.79 to -0.65; P < 0.0001), and Ishihara color plate reading (r = -0.68; 95% CI, -0.79 to -0.66; P < 0.0001) were each strongly and highly significantly correlated with the diagnosis and degree of RAPD. Brightness sense and red perception were each able to discriminate almost all the area under ROC for the diagnosis of RAPD (area of 0.99; 95% CI, 0.98-1.00; P < 0.0001; area of 0.93; 95% CI, 0.90-0.96; P < 0.0001, respectively). Sensitivity and specificity of brightness sense in detection of RAPD were 99% (95% CI, 0.97-1.00) and 95% (95% CI, 0.91-0.98), respectively. The red perception test was only slightly less accurate. CONCLUSIONS. Rapid, simple assessments of brightness sense and color perception provide accurate methods to facilitate the diagnosis of optic neuropathy and may prove to be valuable in screening for optic neuropathy or alternatives to the swinging flashlight test.