Automated tritan discrimination sensitivity: a new clinical technique for the effective screening of severe diabetic retinopathy.

We have developed and extensively assessed an automated chromatic discrimination test which can be used to screen effectively a diabetic population for sight threatening diabetic eye disease. Equiluminant, sinusoidal, low spatial frequency, chromatic gratings are produced along a tritan confusion axis under computer software control on a high resolution CRT. The correct position of the tritan axis in colour space was calibrated using subjects whilst they were transiently tritanopic. The minimum amplitude about a neutral "grey point" along the tritan confusion axis at which a subject can just distinguish a grating is found using a double staircase reversal algorithm. This measure is taken as the Tritan Discrimination Sensitivity and it is this that we use to flag those diabetics with severe diabetic retinopathy. This computerised tritan discrimination test is quick, non-invasive, easy to operate, inexpensive and reliable. The test-retest reliability coefficient (rho) is 0.92. The tritan discrimination test effectively identifies those diabetics who have or are most at risk of developing severe diabetic retinopathy. The sensitivity of the test for the detection of maculopathy, ischaemic retinopathy (pre-proliferative), and proliferative retinopathy is 97%, 65%, and 93%, respectively. The corrected specificity of the test is 83%. We conclude that the tritan discrimination test has potential for use as a valuable screening tool for the early detection and treatment of severe diabetic retinopathy.