BACKGROUND: Changes in retinal vessel caliber are crucial for detecting early retinopathy, a significant cause of blindness in individuals with Diabetes Mellitus type 2 (T2DM). This study aims to evaluate the changes in retinal vessel caliber and identify factors associated with these changes in recently diagnosed T2DM patients. METHODS: The study included newly diagnosed T2DM patients (within 6 months of diagnosis) who were free of antidiabetic treatment (except metformin) and matched individuals based on age and blood pressure (BP). Data collected included somatometric measurements, BP (office and 24-h), hematological data, albuminuria (via 24-h urine collections), ten-year atherosclerotic cardiovascular disease risk (ASCVD score), endothelial dysfunction (measured by Asymmetric Dimethylarginine, ADMA), retinal microvascular changes, assessed as central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE), and arteriovenous ratio (AVR) using specialized software on nonmydriatic fundus photographs. RESULTS: The study involved 87 T2DM patients and 90 controls, aged 57±11 years. Key findings include no significant differences in CRAE, CRVE, and AVR between T2DM patients and controls. Age (P=0.019) and nighttime systolic BP (SBP) (P=0.002) were independent predictors of AVR. CRAE was independently associated with nighttime SBP (P=0.048). CRVE was independently associated with age (P=0.016), dipping (P=0.002), and smoking (P=0.018). In normotensive subjects, AVR was significantly lower in T2DM patients (P=0.035). CONCLUSIONS: The study concludes that increased nighttime SBP is a more critical factor than hyperglycemia in affecting retinal vascular caliber changes in newly diagnosed T2DM patients. This highlights the importance of managing nocturnal hypertension to prevent retinal damage in this patient population.