Quantitative Analysis of Capillary Density in High Myopia Patients with Diabetic Retinopathy: A Retrospective Monocentric Study Using OCT-A

Objective - Diabetic retinopathy (DR) is a major microvascular complication of diabetes, characterized by retinal capillary alterations and progressive ischemia. Some epidemiological studies based on fundus examination have suggested a protective effect of high myopia (HM) against the development and progression of DR. This study aims to quantitatively analyse retinal capillary density and non-perfusion areas in highly myopic patients with DR, comparing them to emmetropic diabetics and highly myopic non-diabetics using Optical Coherence Tomography Angiography (OCT-A). Methods - In this retrospective, monocentric, observational study, we included patients with type 1 or type 2 diabetes and high myopia (HMDB). We also included matched emmetropic diabetic patients (DB), as well as matched non diabetic subjects with high myopia (HM). High myopia was defined as an axial length > 26 mm and/or refraction ≤ -6D. Superficial and deep capillary density, as well as the area of the foveal avascular zone, were assessed using a 3x3 mm OCT-A scan (Optovue®, AngioAnalytics software). Results – Twenty-six eyes of 15 patients were included in the HMDB group, 26 eyes of 15 patients in the DB group and 26 eyes of 16 patients in the HM group. Superficial capillary plexus (SCP) density was significantly lower in both HM and HMDB groups compared to DB. However, no significant differences were found between HM and HMDB. Deep capillary plexus (DCP) density was significantly lower in HM compared to DB, while HMDB showed higher DCP values than HM, suggesting a distinct vascular profile. No significant differences were observed in foveal avascular zone (FAZ) area across groups. Adjusted models showed SCP decreased with diabetic retinopathy (DR) severity, while DCP showed a non-significant decreasing trend. In the HMDB group, DCP appeared elevated at earlier stages but declined with increasing pathology. Discussion – Our findings suggest that diabetes and HM have distinct and potentially interacting effects on retinal microvasculature. The preservation of DCP in HMDB may reflect early compensatory vascular remodeling. This supports a model where DCP is relatively spared in early-stage DR among individuals with HM, followed by capillary dropout as disease progresses.