Hovering Hyalocytes: Tracking Pre-Retinal Hyalocyte Displacement in Unaffected Controls and Sickle Cell Disease (SCD) Patients Using Clinical OCT.

Abstract

Purpose : Hyalocytes are resident tissue macrophages within the vitreous involved in immune surveillance, media clarity, and response to metabolic disruptions. Once mobilized to areas of distress, they become activated, less mobile and transform. Here we demonstrate the ability to track cells over one hour using clinical OCT in normal subjects and patients with sickle cell disease, and to assess the influence of different SCD genotypes On their mobility.

Methods : Hyalocytes from 40 SCD patients (genotypes: 9 HbSC, 27 HbSS, & 4 HbS) and 24 race-matched unaffected controls were imaged at 2 sessions (baseline and 1 hour follow up) using a clinical SD-OCT device (Avanti RTVue-XR; Optovue). At each session, 10 3x3mm scans located at ∼9deg temporal to the fovea were acquired and averaged (PMID: 32574351). Hyalocytes were identified and tracked over 1 hour on a 1x1mm region of interest (Fig A1-2 & B1-2). Cell displacement was performed on an averaged 3µm OCT reflectance (OCTR) slab located above the inner limiting membrane at each session using the TrackMate plugin in ImageJ (PMID: 35654950). Cell displacements over 1 hour were then computed after the correction of OCTR scan dimension based on individual axial lengths.

Results : A total of 2041 hyalocytes were identified and tracked. Median ± interquartile range of hyalocyte displacement over 1 hour in Controls, HbSC, HbSS, and HbS were 13.58±17.86µm, 10.61±10.65 µm, 12.86±17.0 µm, and 9.87±13.25 µm, respectively. Statistical significant difference in hyalocyte displacement was found among groups (Kruskal-Wallis test, p < 0.0001). Pairwise comparisons showed no statistical significance between Controls and HbSS (p=0.586). However, HbSC and HbS showed significantly lower hyalocyte displacement, as compared to controls and HbSS (Controls vs HbSC, p<0.001; Controls vs HbS, p=0.001; HbSS vs HbSC, p=0.006 (Fig A3 & B3); HbSS vs HbS, p=0.031).

Conclusions : Hyalocyte displacement was significantly less in patients with HbSC genotype, in contrast to those from patients with HbSS. This appears consistent with the greater degree of clinical retinopathy seen in patients with HbSC compared to those with HbSS, and suggests a role for hyalocytes in sickle retinopathy. Monitoring hyalocyte mobility and distribution could be a promising strategy for evaluating level of disease activity or response to therapeutics

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.