Diabetic retinopathy (DR) is more than a capillary disorder. Diabetes affects neurons, glial cells, vascular cells, and immune signals within the retinal neurovascular unit (NVU). Retinal neurovascular coupling (NVC) is a useful functional marker of NVU integrity because it reflects the rise in local blood flow that follows neural activity. Many human flicker-light studies report smaller vessel dilation or weaker flow responses in diabetes. This finding can appear even in patients without clear fundus lesions. When NVC is reduced, retinal tissue may receive less oxygen. Lower oxygen delivery can raise oxidative stress and promote inflammation. These changes can then worsen vascular injury. This review describes key NVC pathways and diabetes-related NVU changes in Müller glia, astrocytes, microglia, pericytes, and endothelial cells. The review highlights sympathetic activation as a common stress signal. Pain, anxiety, perioperative stress, and sleep loss can increase sympathetic activity and circulating catecholamines. In the diabetic retina, vascular reserve is often limited. Under these conditions, catecholamines can increase mural cell constriction, reduce nitric oxide (NO)-dependent relaxation, and increase endothelial activation and barrier strain. These effects can shift the baseline state of glial and immune cells and further weaken NVC. The review also summarizes translational tools that can test these links. These tools include heart rate variability, standardized NVC protocols with diameter and flow measures, and retinal organoid and organ-on-a-chip platforms with controlled adrenergic exposure. The review discusses perioperative care packages that reduce stress responses, protect sleep, and manage glucose as practical ways to support retinal microcirculation. More longitudinal human studies are still needed. Retina-specific perioperative endpoints are also needed to clarify causality and to guide intervention trials.
Tan et al. (Mon,) studied this question.