SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IMAGING OF THE CHORIOCAPILLARIS

Purpose: To analyze swept-source optical coherence angiography images acquired at different depths above and below the default location of the Zeiss PLEX Elite 9000. Methods: Normal eyes of subjects in their 20s and 30s were evaluated. Angiographic slab images were taken at the default location of 29 mu m to 49 mu m below the retinal pigment epithelium and 21 mu m to 41 mu m through 52 mu m to 72 mu m below in steps. The images were processed using the projection removal function from the device's software. Raw images were evaluated, as were images that underwent a published compensation technique that adjusts for light penetration to the sampled layer. Results: Eleven eyes of 11 subjects were evaluated for the uncompensated and the compensated sets with the projection removal function turned off and on. The default location, 29 mu m to 49 mu m below the retinal pigment epithelium, showed a granular choriocapillaris appearance. This appearance remained in all slabs from each group, differing slightly throughout depth. The projection removal function modified the grayscale values and diminished projection from overlaying retinal vessels. The compensation technique altered the appearance of flow deficits, and the changes induced by it were more evident on the images were the projection removal function was turned on. Conclusion: Flow images in swept-source optical coherence angiography of the choriocapillaris from varying levels are similar in appearance, suggesting projection from the choriocapillaris is important in image formation, although layers of vessels in the inner choroid may contribute by various amounts. A model explaining the prominent projection artifacts observed in the choroid with swept-source optical coherence angiography imaging is presented.