Type 2 Diabetes is a leading cause of blindness in working-aged Americans. Vision loss comes from diabetic eye disease which includes diabetic retinopathy and edema. Diabetic eye disease can appear at any retinal location and damages both the inner and outer retina. There are no treatments outside of glycemic control for early diabetic eye disease. Methods for early diagnosis and detection, especially if location-specific, are important as they can help doctors and patients to be proactive in delaying retinopathy and vision loss. Current clinical tests such as multifocal electroretinograms (mfERG), ocular coherence tomography (OCT), and color vision assessment have been widely shown to be altered in early diabetes. However, there has been little work to characterize localized color vision deficiencies across the diabetic retina, and it remains unclear exactly which cells are implicated in color vision losses. To address these gaps, the proposed research will test patients using a custom chromatic microperimeter to precisely quantify color discrimination across the visual field. In Aim 1, color thresholds from patients with diabetes and prediabetes will be shown to differ from normally sighted control subjects, with the degree of impairment and variation in testing correlated with HbA1c levels. In addition to expected reductions in the blue-yellow pathway, it is hypothesized that the red-green pathway will show a deficiency as well, addressing the controversy concerning whether S-cone loss alone underlies the color vision deficits in diabetes. In Aim 2, additional co-registered structural and functional measures from mfERG, OCT, and fundus photography will reveal that spatially localized losses are associated with regions of damage, laying the foundation for future longitudinal studies aimed at the early detection of affected regions in diabetes and prediabetes. The ability to predict which areas are most affected could constitute a significant advance in diagnosis and management of this disease and potentially create new end points for future studies and trials. Diabetes has reached epidemic proportions in the US and worldwide and better understanding the effects of the disease could lead to improvements in the lives of these patients.