Choriocapillaris Thinning in Myopic Macular Degeneration Revealed by Swept-Source Optical Coherence Tomography C-Scan Imaging

Background: The choriocapillaris (CC), which supplies the outer retina, may be involved in myopic macular degeneration (MMD); however, quantitative in vivo assessment remains challenging. This study aimed to quantify CC thickness (CCT) with swept-source optical coherence tomography (SS-OCT) C-scan imaging and to characterize its changes in MMD. Methods: This study grouped participants into control (CN), simple high myopia (SHM), and pathological myopia (PM) groups. Each group included 30 eyes. Swept-source optical coherence tomography was used to obtain 3 × 3 mm volumetric scans. The choriocapillaris was segmented from the en-face (C-scan) images to determine its thickness and its coefficient of variation. The choroidal thickness (CT), luminal volume, stromal volume, and choroidal vascularity index were quantified from the volumetric data. Results: Reproducibility was excellent (intra- and inter-grader ICCs 0.987 and 0.970). CCT was lower in PM than in CN and SHM (mean differences 9.94 µm and 7.95 µm; both p < 0.001) and slightly lower in SHM than in CN (1.99 µm; p = 0.005), together with increased coefficient of variation in PM. CT and axial length were independently associated with CCT (p = 0.002 and 0.020, respectively). Mediation analysis indicated that choroidal thickness accounted for approximately 52.5% of the association between axial length and choriocapillaris thickness (p < 0.05). CCT distinguished PM from SHM with excellent performance (AUC = 0.996; cutoff 8.9 µm). Conclusions: Choriocapillaris thickness was significantly reduced, with increased relative spatially heterogeneous in MMD. It was associated with axial length and choroidal thickness and showed excellent discriminatory performance.