Assessing vitreous cortex hyalocyte morphology and dynamics in the living human eye

Abstract

Purpose : Hyalocytes are the resident macrophages of the vitreous. They have been implicated in the maintainence of vitreous transparency, response to injury, and involvement in extra-retinal proliferations (PMIDs: 14160361; 32574351; 33168747). Little, however, is known about the behavior of these transparent cells within their native environment, due to the lack of adequate methods of visualization. In this study, we employed a novel imaging system and image processing technique to reliably observe and characterize these cells in living human eyes over time.

Methods : Five healthy subjects were imaged using a non-confocal quadrant-detection adaptive optics scanning light ophthalmoscope (AOSLO) (PMID: 33680539). A 1x1° region of interest (ROI) at the temporal retina was imaged every 5 minutes over 1 hour for a total of 13 time points. To study hyalocyte morphology and movement over time, image registration and cell tracking were performed on all acquired images using ImageJ. Cell velocities were calculated from distances traveled divided by the time elapsed between time points. Hyalocyte morphology and movements over a longer timespan were also evaluated by imaging the same ROI 4 months after the first visit in 2 subjects.

Results : A total of 50 hyalocytes were imaged. Cells demonstrated variability in morphology and movement over time (Fig). Five categories of morphology, described in microglia, were observed, specifically: ramified (74%), hyper-ramified (6%), rod (4%), activated (14%), and amoeboid (2%). Mean±stdev velocities of ramified, hyper-ramified, rod, activated, and amoeboid cells were 0.43±0.22, 0.59±0.30, 1.29±0.40, 1.35±1.21, and 0.26 (one cell only) μm/min, respectively. In the 2 subjects imaged over 4 months, similar numbers of cells were visualized within the same ROI. However, cell tracking between visits could not be confirmed due to substantial variation in cell morphology and location, as well as absence of definitive cell labels.

Conclusions : We have demonstrated the ability to visualize hyalocytes in the living human eye without exogenous labeling using a quadrant-detection adaptive optics scanning light ophthalmoscope. The non-invasive characterization of hyalocyte morphology and movement dynamics may provide better understanding of the roles these cells play in disease progression and response to pharmacologic treatment.

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