Human retinal pigment epithelium cells can be imaged in vivo with a novel adaptive optics camera using transscleral illumination

Abstract

Purpose : Histopathology studies described morphological changes of the retinal pigment epithelium (RPE) specific to the onset and progression of retinal diseases in human eyes. However to date, no valuable imaging tool is used in the clinic to image RPE cells. Transscleral Optical Imaging (TOI) uses an oblique illumination of the fundus combined with adaptive optics to provide cell-resolution images of the retinal layers up to the RPE, in vivo. A prospective study was carried out to assess safety and repeatability of TOI technology and characterize healthy RPE cells.

Methods : Eyes of subjects above 18 years presenting normal fundus check were examined with Cellularis^®, a novel retinal camera prototype for TOI. For each eye, 6 images of the RPE cells were acquired at different locations of the macula (Fig. 1), one of them being imaged 5 times to evaluate the repeatability of the method. Baseline and follow-up ophthalmic exams were performed before and 1-3 weeks after TOI to assess safety. RPE cell features were extracted with a custom software. Spearman test was used for statistical analyses.

Results : 49 eyes (mean axial length (AL): 24±0.9 mm; mean refractive error: -1±1.7) of 29 subjects (mean age: 37±13.3 years; 19 males) were included. No safety issue was reported during the study. RPE cells were characterized by density of 3663±274 cells/mm², cell area of 233±17.1µm², intercellular distance of 16±0.6µm and number of neighbor cells around 6, in average. Longer AL significantly correlated with decreased cell density (Spearman’s correlation coefficient (R)=-0.757; p<0.001), increased cell area (R=0.667; p<0.001) and increased intercellular distance (R=0.763; p<0.001). Similarly, aging significantly correlated with decreased cell density (R=-0.385; p<0.05), increased cell area (R=0.460; p<0.05) and increased intercellular distance (R=0.391; p<0.05). Interestingly, age also correlated with cell morphological features, showing decreasing circularity (R=-0.611; p<0.001) and increasing elongation (R=0.587; p<0.001) with increasing age. Mean coefficient of variation for repeated images was below 4% for each of the features.

Conclusions : TOI allows safe and repeatable in vivo imaging of human RPE cells, consistent with the literature, paving the way for establishing a full RPE normative database.

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

 

Overview of the 6 macular locations and corresponding RPE images for 2 of them