Transscleral Optical Phase Imaging of the Human Retina - TOPI

The in vivo observation of the human retina at the cellular level is crucial to detect lesions before irreversible visual loss occurs, to follow the time course of retinal diseases and to evaluate and monitor the early effects of treatments. Despite the phenomenal advances in optical coherence tomography (OCT) and adaptive optics systems, in vivo imaging of several retinal cells is still elusive. Here we propose a radically different method compared to OCT, called transscleral optical phase imaging (TOPI), which allows to image retinal cells with high contrast, high resolution, and within an acquisition time suitable for clinical use. TOPI relies on high-angle oblique illumination of the retina, combined with adaptive optics, to enhance the phase contrast of transparent cells. We first present in-vivo images of retinal cells, from the retinal pigment epithelium (RPE) to the nerve and vascular layers of the retina, in eleven healthy volunteers without pupil dilation. The morphology of the cells in vivo is then compared to that of images obtained with the same technique applied on ex vivo human RPE and pig retinas. Finally, we demonstrate the ability of high resolution phase microscopy to image pericytes and microglia around rat retinal capillaries. Our results show the ability of TOPI to image and quantify retinal cells up to the RPE depth within a maximum time of 9 seconds over a field of view of 4.4 x 4.4{\deg}, opening new avenue in the in vivo exploration of the deepest layer of the retina in healthy and diseased eyes.