To analyze swept-source optical coherence angiography slab images acquired at the default level for the choriocapillaris from the Zeiss PLEX Elite 9000 before and after using a previously described imaging compensation technique.
Eyes of normal subjects, in their 20 seconds and 30 seconds, were evaluated. Angiographic slab images, 20 µm in thickness, were taken at the default location of 29 to 49 µm below the retinal pigment epithelium. These images were evaluated, as were images that underwent a published compensation technique that adjusts for light penetration to the sampled layer. Each set of images was threshold at 1 SD below the mean. Visual comparison of the swept-source optical coherence angiography images along with a quantitative analysis using a novel parameter known as multiscale structural similarity index, a measure of image similarity, was performed.
Eleven eyes of 11 subjects were evaluated. The default location, 29 µm to 49 µm below the retinal pigment epithelium, showed the granular choriocapillaris appearance. Visual comparison showed that the compensation technique altered the appearance of the thresholded images, creating the appearance of new deficits while causing others to disappear. The mean multiscale structural similarity index for the original versus thresholded images and original versus thresholded compensated was 0.49 and 0.34, respectively, representing a statistically significant difference.
The findings of this study show that the use of a commonly used imaging compensation technique can have undesired effects on the image, and its use should be carefully considered. A model explaining the cause of such changes in the choriocapillaris swept-source optical coherence angiography images is presented.