Early visual changes in diabetic patients with no retinopathy measured by color discrimination and electroretinography

Early visual changes caused by diabetes include color vision losses and an abnormal full-field electroretinogram. The purpose of this study was to evaluate color vision in type 2 diabetic patients with no clinically detectable retinopathy using an objective psychophysical color vision test, evaluate retinal function assessed by full-field electroretinography (ffERG), and verify the agreement among the changes detected by each of these tests. Color vision was tested and ffERG was performed in 34 diabetic patients (20 males; ages 56 ± 9 years). Results were compared with those obtained from age-matched control groups. Color discrimination losses occurred in all three color-confusion axes with a higher incidence on the protan axis. The fullfield electroretinographic data indicated that inner retinal components (i.e., ffERG oscillatory potentials) were more affected than outer retinal components, indicating impairment of secondand third-order retinal neurons early in the disease. Previous studies reported tritan losses as a classic color vision defect in diabetes, but our results showed that all three color-confusion axes (i.e., protan, deutan, and tritan) are compromised, at least during the very early stages of the disease, reflecting a diffuse pattern of color vision loss. The full-field electroretinographic results that showed abnormalities of the inner retina support the color vision findings.