New clinical color threshold test for eye disease

Selective loss of sensitivity to blue light, when it is detected by the short wavelength-sensitive cones (B cones), is a common early sign of many retinal and visual pathway disorders. A reliable clinical test is needed to allow detection of this defect. We describe a new, simple forced-choice clinical test of B cone function which is brief, reliable, and free of patient criteria for seeing. Test results are relatively unaltered by up to 2 D of uncorrected refractive error and the usual small fixation changes the patient makes during the test. A comparison of three different test results, all obtained within 5 min, allows measurement of R and/or G cone function free of age and individual differences caused by yellowing of the ocular media in the B cone test result. The test has been used to demonstrate B cone sensitivity losses related to the severity of retinopathy in 60 diabetics, as well as selective B cone loss in glaucoma and ocular hypertension.