Abstract
Purpose :
To characterize structural metrics in the healthy human macular choriocapillaris (CC) layer using adaptive optics – optical coherence tomography angiography (AO-OCTA).
Methods :
The AO-OCT channel of the FDA Fourier domain mode-locked multimodal system operating at 3.4 MHz and 13.0 volumes/s was used in angiography mode to image 21 human volunteers (aged 43.1±13.0 years) without any ocular pathology. For each participant, a single 28° (~8.4 mm) strip centered at the fovea was imaged in 11 discrete locations (3°×3° scan field and 2.5° separation) from the rim of the optic nerve head (ONH) to the temporal retina. The slow scanner was set to eight repeat B-scans for each slow scan position, where speckle variance was calculated across the repeat scans to produce the final angiography B-scan. AO-OCTA volumes were flattened to photoreceptor-retinal pigment epithelium (PR-RPE) complex and CC images were extracted (5 axial pixels) and montaged. 1°×1° regions of interest with 1° region separation were further examined across the imaging region to extract vascular metrics including capillary density, capillary diameter, void diameter, void area, and tortuosity.
Results :
We observed a continuous CC capillary network without any large (>100 µm diameter) regions of flow dropout for all healthy participants. The mean values for the healthy cohort for all metrics except tortuosity exhibited variation across the macula. The mean CC density was lowest at the ONH rim (43-45%) and increased slightly from 48% to 53% from nasal to temporal macula. Conversely, the vessel diameter was highest at the ONH rim (13.8 µm) and decreases from 12.9 µm to 12.1 µm. The void diameter and area both decreased from nasal to temporal, where the void diameter measured 15-18 µm at the ONH rim and decreased from 13.3 µm to 11.4 µm. The void area exhibited significant variability near the ONH rim and decreased from approximately 3000 µm2 to 1000 µm2. Tortuosity maintaining a constant value of ~1.16-1.17 across the macula.
Conclusions :
The CC vascular layer, which supplies the PR/RPE complex, is an essential component in retinal metabolic health. However, visualizing CC in the living human eye is challenging due to its tightly interconnected vascular organization and weak reflectance. CC metric characterization in healthy human eyes is a first step in imaging biomarker validation for use in disease diagnosis and treatment strategy formulation.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.