The effect of diabetes mellitus to retinal vascularity in patients without diabetic retinopathy.

Clinical relevance: Understanding early microvascular alterations in the retinal and choroidal structures of patients with diabetes mellitus is essential for the timely identification of high-risk individuals and the prevention of vision-threatening complications.

Background: This study evaluates the impact of diabetes mellitus (DM) on retinal and choroidal vascular structures using optical coherence tomography angiography (OCTA) in pre-retinopathic patients. It also explores the relationship between OCTA parameters and HbA1c levels, a marker of long-term glycaemic control.

Methods: Ninety-five right eyes of pre-retinopathic diabetic patients and 90 right eyes of healthy controls were included. OCTA was used to assess foveal avascular zone (FAZ) area, vascular densities, and retinal flow areas. Subfoveal choroidal thickness (SCT) was measured with enhanced depth imaging (EDI). FAZ shape irregularities, such as border disruptions and loss of circularity, were subjectively analysed. HbA1c levels were recorded, and participants were grouped based on the 8% threshold recommended by the American Diabetes Association.

Results: Vascular densities in both superficial and deep layers were significantly lower in diabetic patients (p < 0.05). The FAZ area was larger in diabetic patients (0.285 ± 0.147 mm² vs. 0.259 ± 0.105 mm², p = 0.029), with irregularities observed in 37% compared to 10% of controls (p = 0.000013). Patients with HbA1c > 8% had significantly larger FAZ areas (p < 0.05). Flow areas and SCT were reduced in diabetic patients (p < 0.05), though no relationship was found between HbA1c and vascular density. Spearman correlation analysis revealed that higher HbA1c levels were positively correlated with FAZ area (p < 0.05).

Conclusion: OCTA demonstrates its utility in detecting early microvascular changes in pre-retinopathic diabetic patients. FAZ enlargement and shape abnormalities, particularly in those with poor glycaemic control, highlight its potential role in identifying high-risk patients. These findings support the integration of OCTA into diabetic screening protocols to optimise patient management and prevent progression to retinopathy.