# Effect of disease duration on foveal microvasculature assessed by OCTA in type 2 diabetes mellitus without clinical diabetic retinopathy

## TL;DR

This study shows that OCTA can detect early microvascular changes in the eyes of type 2 diabetes patients before visible retinopathy occurs.

## Contribution

The study demonstrates OCTA's potential for early detection of preclinical diabetic retinal changes in patients without clinical diabetic retinopathy.

## Key findings

- T2DM patients without DR had significantly reduced parafoveal vessel density in both SCP and DCP compared to non-diabetic controls.
- T2DM patients diagnosed over 10 years ago had lower vessel density than those diagnosed 5-10 years ago.
- OCTA detected enlarged FAZ in T2DM patients, suggesting preclinical microvascular abnormalities.

## Abstract

The objective of this study was to establish a comparison between the vessel density (VD) and foveal avascular zone (FAZ) of patients with type 2 diabetes mellitus (T2DM) who lacked clinical signs of diabetic retinopathy (DR) and non-diabetic patients using optical coherence tomography angiography (OCTA).

A cross-sectional comparative case-control study (unpaired) was carried out at two tertiary hospitals. All subjects underwent optical coherence tomography angiography (OCTA) examination (DRI OCT Triton Swept Source, Topcon, Japan). The average VD in the superficial capillary plexus (SCP) and the deep capillary plexus (DCP), the FAZ area (mm2) in SCP, and DCP were taken into analysis. The time since the diagnosis of T2DM was used to stratify patients with diabetes between 5 and 10 years and those with a diagnosis of more than 10 years.

Compared to non-diabetic controls, the parafoveal VD in both SCP and DCP was significantly reduced in the eyes of T2DM patients without clinical DR (p < 0.001). Additionally, the VD was also statistically reduced in T2DM diagnosed more than 10 years ago compared to T2DM cases diagnosed between 5 and 10 years ago (p < 0.001). The FAZ area in both plexuses was larger in T2DM eyes compared to controls (p < 0.001). The FAZ area was enlarged in DCP (p = 0.04), but there was no significance of FAZ area in SCP when comparing patients with T2DM diagnosed between 5 and 10 years ago to those diagnosed more than 10 years ago (p = 0.06).

In diabetic patients with long-term diagnosed disease, OCTA was shown to be capable of detecting preclinical microvascular foveal abnormalities prior to the development of clinically apparent retinopathy. According to our findings, OCTA has the potential to be a promising instrument for the early detection of vascular micro-abnormalities and the routine screening of diabetic eyes.