Peripapillary circulatory dysfunction precedes structural loss in treatment-naive diabetic retinopathy.

Purpose: The aim of this study was to compare the timing of peripapillary vascular damage between functional and structural parameters and examine their involvement with neurovascular coupling at different stages of diabetic retinopathy (DR).

Methods: One hundred ninety eyes of 143 patients with type 2 diabetes mellitus (DM) and 88 healthy control eyes were enrolled. Eyes of DM patients were divided into 3 stages with no diabetic retinopathy (NDR), non-proliferative diabetic retinopathy (NPDR), and proliferative diabetic retinopathy (PDR). NPDR and PDR eyes were treatment-naive. OCT angiography was used to calculate radial peripapillary capillary (RPC)-flux index (FI) and RPC-perfusion density (PD). Spectral domain OCT was used to measure retinal nerve fiber layer (RNFL) thickness within the corresponding RPC areas.

Results: RPC-FI significantly decreased in NDR eyes compared to control eyes and thereafter remained unchanged among DM (NDR, NPDR, and PDR) eyes. In contrast, RPC-PD stayed unaltered between control and NDR eyes and significantly decreased in NPDR followed by PDR eyes at similar levels. From control to NPDR eyes, RNFL thickness showed positive correlations with both RPC-FI and RPC-PD, indicative of functional and structural neurovascular coupling. These vascular parameters were also correlated with each other in control and NPDR eyes but not NDR eyes, consistent with the difference in the timing of vascular damage between functional and structural parameters.

Conclusions: Circulatory dysfunction preceded structural loss while maintaining peripapillary neurovascular coupling during progression of DR stages. RPC-FI would likely be more sensitive than RPC-PD in detecting early vascular damage in DR.