Glycemic Control and Retinal Microvascular Changes in Type 2 Diabetes Mellitus Patients without Clinical Retinopathy

Background: To investigate the association of glycemic control and retinal microvascular changes in patients with type 2 diabetes mellitus (T2DM) without diabetic retinopathy (DR). Methods: This retrospective, observational, cohort study included patients with T2DM without DR. The patients were categorized into intensive control (IC; mean glycosylated hemoglobin [HbA1c] <= 7.0%) and moderate control (MC; mean HbA1c >7.0%) groups. Optical coherence tomography (OCT) and swept-source OCT angiography (OCTA) image parameters were compared between three groups, including healthy controls. Results: In total, 259 eyes of 259 participants (88 IC, 81 MC, and 90 controls) were included. The foveal avascular zone area was significantly larger in the MC group than IC and control groups (all P<0.05). The IC group had lower vessel density in the superficial retinal layer and deep retinal layer than the controls (all P<0.05). The choriocapillaris (CC) flow deficit (FD) was significantly greater in the MC group than in the IC and control groups (18.2%, 16.7%, and 14.2%, respectively; all P<0.01). In multivariate regression analysis, CC-FD was associated with the mean HbA1c level (P=0.008). There were no significant differences in OCT parameters among the groups. Conclusion: OCTA revealed that early CC impairment is associated with HbA1c levels; the CC changes precede clinically apparent DR. The OCTA parameters differed among the groups according to the degree of glycemic control. Our results suggest that microvascular changes precede DR and are closely related to glycemic control.