Non-invasive in vivo imaging assessment of retinal microglia-like cells in diabetic retinopathy by adaptive optics optical coherence tomography

Abstract

Diabetic retinopathy (DR) is a microvascular, neurodegenerative and inflammatory disorder characterised by retinal microglial activation. In this study, we used adaptive optics optical coherence tomography (AO-OCT) to assess microglia-like cell morphology and density at the inner limiting membrane (ILM) in vivo in eyes with DR and healthy controls. Eleven eyes from nine patients with DR and seven eyes from seven healthy controls were examined using a prototype AO-OCT system. Volumetric images were acquired over a 4°×4° field of view at five standardised retinal locations extending from the superior vascular arcade to the parafovea. For ultrastructural reference, a retinal sample from the foveal region of a 51-year-old donor was analysed using serial block-face scanning electron microscopy (SBFSEM). Retinal microglia-like cells were consistently visualised at the ILM in all participants using single-volume AO-OCT imaging. High-resolution imaging allowed identification of distinct morphological phenotypes consistent with histological findings and SBFSEM observations. The proportion of cells with a reactive morphology was higher in eyes with DR than in controls (median 51% vs. 16%). Overall cell density did not differ significantly between groups but showed considerable interindividual variability. In contrast, a greater proportion of cells were embedded within the ILM in DR eyes compared with controls (median 90% vs. 53%). SBFSEM provided detailed ultrastructural characterisation, revealing fine processes approximately 100–400 nm in diameter extending from the soma of microglia with a reactive morphology, a feature not previously reported. AO-OCT enables three-dimensional, quantitative assessment of microglia-like cell morphology and distribution in healthy eyes and eyes with DR. Eyes with DR showed an increased proportion of cells with a reactive morphology and a greater proportion of cells embedded within the ILM, suggesting increased retinal immune activation. These findings support AO-OCT as a tool for investigating retinal inflammatory changes in DR and other retinal disorders.