Systemic inflammatory markers and neurovascular changes in the retina and choroid of diabetic patients without retinopathy: insights from wide-field SS-OCTA

Purpose The purpose of this study was to investigate the association between systemic inflammation markers and early neuronal and microvascular changes in the retinal and choroidal regions of patients with type 2 diabetes mellitus (T2DM) without clinical signs of diabetic retinopathy (DR), utilizing wide-field swept-source optical coherence tomography angiography (SS-OCTA). Methods This retrospective, observational cohort study included 61 patients (119 eyes) with T2DM without clinical DR (NDR group) and 44 healthy individuals (82 eyes) as controls. All participants underwent a comprehensive ophthalmic evaluation and blood sampling for hematologic indices. Inflammatory markers, including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI), were calculated. The mean thickness of the retina, choroid, and individual inner retinal layers, as well as the vessel density measurements of the superficial and deep retinal layers, and the choriocapillaris perfusion area, were recorded and analyzed from the OCTA images. Additionally, the choroidal vascularity index (CVI) was determined. Results The NDR group demonstrated significantly higher levels of NLR, SII, and SIRI compared to the control group ( p < 0.05). The diabetic cohort showed reduced vessel density in the deep capillary plexus (DCP) across all measured regions ( p < 0.05). Significant but weak negative correlations were observed between inflammation markers, particularly NLR, and OCTA parameters, with a marked impact on the DCP ( r = −0.21 to −0.32, p < 0.05) and CVI ( r = −0.23 to −0.28, p < 0.05). Conclusion The study provides new insights into the role of systemic inflammation in early structural and blood flow changes in the retina and choroid, occurring prior to the onset of DR. The findings highlight the importance of inflammation in the pathogenesis of DR, even in the absence of clinical signs, suggesting that systemic inflammatory markers may serve not only as early biomarkers of ocular changes in T2DM but also as potential early therapeutic targets to prevent or delay diabetic retinopathy.