Imaging photoreceptor/RPE/choriocapillaris complex with adaptive optics optical coherence tomography

Abstract

Purpose : Histopathological studies have shown that age-and disease-related changes in the photoreceptor/retinal pigment epithelium/choriocapillaris (PR/RPE/CC) complex begin at the molecular and cellular levels. Thus, detection and monitoring at this scale provide the greatest promise for improved diagnosis and intervention. Here we demonstrate that cellular-level morphometry of this complex in normal eyes and eyes with drusen can be achieved using adaptive optics-optical coherence tomography (AO-OCT).

Methods : Two healthy subjects (24 and 50 years old), and a third (68 years old) with small (<63 µm) to medium drusen (>=63 µm to <125 µm) were imaged with the Indiana AO-OCT system. The system operated at a 500 KHz or 1 MHz A-line rate and acquired multiple AO-OCT volume videos of the same patch of retina at 7° temporal to the fovea. To enhance RPE cell contrast, AO-OCT volumes with an interval of more than 3 s were selected for post processing to allow organelle motility to decorrelate speckle between volumes. A custom OCT angiographic method was applied to enhance contrast of CC vessels. AO-OCT volumes were registered and averaged in all three dimensions using a GPU-accelerated, 3D-image-registration algorithm. This approach preserved the one-to-one mapping of cellular structure across the entire depth of the PR/RPE/CC complex. From the processed AO-OCT volumes, density measurements were extracted for cone photoreceptors, RPE cells, and CC capillaries, the latter defined as the ratio of lumen area to total area in the en face image of CC.

Results : Photoreceptors, RPE cells, and CC capillaries were successfully individuated in all subjects. Measured densities for the two healthy subjects without drusen were 10,654 and 7384 cells/mm² (cones); 5,036 and 3,964 cells/mm² (RPE cells); and 62% and 53% (CC). Measured densities at regions adjacent to a 50 µm drusen in the third subject were 8,550 cells/mm² (cones), 4,494 cells/mm² (RPE), and 44% (CC). Above the drusen, cone and RPE cells were visible, and cone density was 8,303 cells/mm². Interestingly of the six small drusen detected with AO-OCT in the imaged 1.5° x 1.5° retinal patch, only one was detected with Spectralis OCT.

Conclusions : AO-OCT combined with intensity and angiographic processing enables visualization and morphometric analysis of cellular structures that compose the PR/RPE/CC complex even around drusen.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.