Transscleral Optical Phase Imaging of healthy human Retinal Pigment Epithelium

Abstract

Purpose : The retinal camera using Transscleral Optical Phase Imaging (TOPI) provides in vivo images of retinal pigment epithelium (RPE) cells. We performed a clinical study to characterize healthy RPE cells and to assess the repeatability and the safety of the RPE imaging.

Methods : Healthy volunteers were recruited. After a standard eye examination, spectral domain optical coherence tomography, infrared, autofluorescence and color fundus imaging, they underwent TOPI examination. Six 5.04x5.04°, high resolution, in vivo images of RPE cells at different locations, associated with 30x30° infrared reflectance images, were acquired per eye. The ophthalmic examination was repeated 1 to 3 weeks after TOPI. RPE images were analyzed with a custom automated software to extract cell features. The coefficient of variation (CoV) of three parameters was established on 31 areas, imaged 3 to 7 times and realigned.

Results : Included were 52 eyes (axial length 24.1±0.96 mm) of 31 participants (age 36.5±13.2 years, range 21-70; 20 males, 11 females). Multimodal imaging showed no difference before and after TOPI. The cell features extracted from the RPE images covering an eccentricity of 1.9° to 16.9° from the fovea were: RPE density 3610±321 cells/µm², cell area 238±23 µm², intercellular distance 14.3±1.1 µm, circularity 0.88±0.019, elongation 0.63±0.025, border distance CoV 0.16±0.013, solidity 0.95±0.001. The number of neighboring cells was close to 5.7±0.1 whatever the age, eccentricity and axial length. Cell density remained constant with age and eccentricity, while it decreased with axial length (R²0.62). Morphological features slightly varied with age, with reduced circularity (R²0.22), increased elongation (R²0.21) and border distance CoV (R²0.22). The CoV calculated for density, area and intercellular distance were 3.9±1.7%, 4.4±1.9% and 2.7±3.1.

Conclusions : The present study demonstrates that in vivo human RPE imaging using TOPI is safe and repeatable. The quantitative analysis provides the first and significant database of in vivo RPE cell features, consistent with the previous in-vivo studies on RPE cells, that can be used as normative database for future diagnostics of retinal diseases at the single cell level.

This is a 2021 ARVO Annual Meeting abstract.

 

Representation of the 6 locations of the RPE images: four centered on the fovea at an eccentricity of 3.8° (1-4), one foveal (5) and one to the discretion of the investigator (6).