Background: Functional visual deficits can occur in patients with diabetes mellitus who show no visible morphological alterations in the retina. In this study we examined the colour vision of diabetic patients using metameric matches. Patients with and without retinopathy, as well as those who had been treated with laser photocoagulation, were examined to ascertain how the functional alterations in the diabetic eye alter with disease status.
Methods: Rayleigh (red-green) and Moreland (blue-green) metameric matches were determined in a total of 51 diabetic patients (24 patients with no retinopathy, 12 patients with background retinopathy and 15 patients who had undergone laser therapy). Their results are compared to those of a control group of 25 subjects with normal colour vision.
Results: A deficit in blue-green colour discrimination found in patients without retinopathy becomes worse with the appearance of vascular alterations in the retina. There is also a significant shift towards green in the Rayleigh match midpoint and towards blue in the Moreland match midpoint, which is at least in part explicable by alterations in lens opacity. Patients who have undergone laser therapy show, on average, better colour discrimination than those with retinopathy, but there is a large variation in their results.
Conclusion: The alterations in the colour vision of diabetics indicate that at least the early functional changes are occurring at an inner retinal location. Lens opacity changes also play a large role as the age of the patients increases.