In swept-source optical coherence tomography angiography (OCT-A) imaging of the choriocapillaris, the signal retrieved is dependent on the reflective properties of deeper tissue, and may be contaminated by projection and direct imaging of vessels immediately below the choriocapillaris, a report published in Retina shows.

The technology does provide especially robust images from default locations of 29 µm to 49 µm below the retinal pigment epithelium (RPE), suggesting that projection from the choriocapillaris is essential for image formation, according to the study results. 

The choriocapillaris is a single-layer dense capillary network located directly below the RPE and Bruch’s membrane complex. Although OCT-A has the potential to provide imaging to better understand the structure of the choriocapillaris, angiography segmentation slabs used are often much thicker than the choriocapillaris. This implies that OCT-A images of the choriocapillaris rely on direct imaging to obtain enough signal to image flow. 


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To confirm this, a team of investigators conducted a retrospective cohort study in which they evaluated normal eyes with swept-source OCT-A at a range of levels to better understand image formation. 

The researchers included 11 eyes from 11 participants (mean age, 28 years; 8 women), performing compensated and uncompensated imaging with projection removal function turned on and off at 5 different levels (21-41 µm, 29-49 µm, 37-57 µm, 45-65 µm, and 52-72 µm). The granular image associated with the choriocapillaris appeared from 21 µm to 41 µm, but it was clearer at the default location between 29 µm and 49 µm, and the appearance remained in all deeper slabs from each of the levels. All of the sections were below the actual levels sectioned due to their anatomical location. 

Appearance of the angiographic slabs was changed due to the projection removal function, as it diminished projection for overlying retinal vessel predominantly, on more superficial sections, and altered grayscale values. The appearance of low deficits was altered by the compensation technique, and the changes were more apparent on the images where projection removal function was turned on. 

Study limitations included the small sample size and the potential for the OCT instrument to have variability. 

“The use of a previously reported image compensating technique can have undesired effects on the image, and its use should be carefully considered,” investigators conclude. 

Disclosure: Multiple study authors declared affiliations with the biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.  

Reference 

Ledesma-Gil G, Fernández-Avellaneda P, Spaide RF. Swept-source optical coherence tomography angiography imaging of the choriocapillaris. Retina. 2021;41(7):1373-1378. doi:10.1097/IAE.0000000000003109