Imaging retinal microglial cell dynamics in healthy and diseased eyes in vivo with adaptive optics

Abstract

Purpose : We recently showed that a refined sequential detection pattern for multi-offset adaptive optics scanning light ophthalmoscopy (AOSLO) can increase the contrast of weakly scattering inner retinal structures, including presumed microglial cells. However, sequential detection was still time-consuming, preventing dynamics from being monitored over short intervals (< 3 mins). Here we show that fiber-bundle (FB) detection AOSLO overcomes this limitation to reveal microglia and immune cell dynamics in healthy and diseased retinas.

Methods : We designed and implemented a custom 7-fiber optical FB in AOSLO that allows for simultaneous confocal and multi-offset detection. We imaged the nerve fiber layer at several locations at multiple timepoints (from minutes to weeks) in 5 healthy participants and in 3 patients with ocular syphilis or uveitis. Microglia and immune cells were manually segmented for quantification.

Results : Fiber-bundle detection reduced single acquisition time to 10-20 sec, permitting improved imaging over larger areas and monitoring of dynamics over short intervals. Microglia in healthy retinas ranged in size from 7 to 19 μm (mean:13 μm) and appeared in two distinct morphologies including rounded cells and elongated cells with visible processes. Microglia moved slowly in healthy eyes (0.05 μm/sec on average), but their motility was increased in patients with active infections or inflammation up to 0.34 μm/sec. Macrophage-like cells containing granular internal structures were seen in an eye with acute syphilitic posterior placoid chorioretinitis. Images were acquired at multiple time points during treatment, decreases in the quantity and motility of microglia were correlated with improvements of vision and other biomarkers. Microglia activity was apparent in an eye affected by acute retinal vasculitis but absent in another patient’s eye affected by a chronic course of retinal vasculitis that was quiescent at the time of imaging.

Conclusions : FB-AOSLO has revealed the fine-scale structure and dynamics of microglia in the retina during active infection and inflammation in the living eye for the first time. FB-AOSLO offers promise as a powerful tool for detecting and monitoring retinal inflammation and infection in the living eye over short timescales. FB-AOSLO may be useful for distinguishing cases of active infection/inflammation and for evaluating response to treatment.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.