Repeatability of the C-100 colour vision test.
BACKGROUND: The C-100 colour vision test has been shown to have a high validity for diagnosing the type of red-green colour vision defect, however, there is little information on the repeatability of the test. This study examines the repeatability of the C-100 in classifying the colour vision defect as either protan or deutan. METHODS: The C-100 was administered on two occasions to 58 subjects with congenital red-green colour vision defects. The sessions were separated by a minimum period of 10 days. RESULTS: The repeatability of the C-100 was high with a kappa coefficient of agreement for diagnosis of 0.96. The few discrepancies were misclassifying protans as deutans. CONCLUSION: The C-100 is a highly repeatable test in terms of separating protans from deutans. However, if a discrepancy occurs, it is more likely to be a protan misclassified as a deutan rather than vice versa.