Diabetic retinopathy (DR) is the leading cause of irreversible blindness in working-age adults. However, DR can only be diagnosed once changes to the retinal vasculature are visible using non-invasive imaging, and available treatments can only slow eventual blindness. Previous studies suggest that neurodegeneration may precede damage to the retinal vasculature, specifically damage to retinal ganglion cells (RGCs). ON and OFF-sustained alphas, two types of RGCs, were examined because they are known to be affected by other retinal diseases and place a high metabolic load on the retina. Mice were injected with streptozotocin to induce a model of type 1 diabetes. The responses of ON and OFF sustained alpha RGCs to a spot stimulus were recorded using cell-attached electrophysiology experiments, and select cells were morphologically analyzed using Sholl analysis. Both diabetic ON and OFF sustained alpha RGCs exhibited abnormal firing rates, and diabetic ON alphas displayed dendritic shrinkage. These results constitute the earliest neurodegenerative effects of DR recorded in mice. The identification of subtle DR symptoms that precede obvious visual deficits is an important step in developing diagnostic tools and pharmacological treatments to prevent long-term vision loss.