Impact of Optical Coherence Tomography Scan Pattern and Chorio-Scleral Interface Delineation on Choroidal Vascularity Index Measurements

Purpose: To compare radial and horizontal raster acquisition patterns using spectral-domain optical coherence tomography (OCT) for assessing choroidal vascularity index (CVI) in healthy eyes and to evaluate how variability in chorio-scleral interface (CSI) delineation influences CVI measurements. Methods: OCT images of 25 eyes from 25 healthy adults were acquired using 12-line radial and 31-line horizontal raster scans with enhanced depth imaging. CVI was measured manually using three different posterior boundaries—defined as the upper (vascular), middle (vascular–stromal) and lower (stromal) CSI boundaries. Agreement between CSI boundaries and scan patterns was assessed using Bland-Altman analysis. Topographical CVI variations across 6-mm Early Treatment of Diabetic Retinopathy Study (ETDRS) subfields, quadrants and rings were evaluated using two-way repeated-measures ANOVA. Results: Participants were aged 21–31 years (72% female; mean spherical equivalent −2.97 ± 2.02 D). Mean CVI differences ranged from 1.43 to 2.38% between the upper and middle CSI boundaries and from 1.23 to 2.04% between the middle and lower CSI boundaries. Comparisons between the upper and lower CSI boundaries resulted in larger CVI differences, ranging from 2.90 to 4.42%. The coefficient of variation for CVI was low (<2%) between radial and raster scan patterns, and Bland-Altman analysis showed overall good agreement. The 31-line raster scan measured 0.51% higher CVI in the central foveal region, whereas the 12-line radial scan yielded 0.64–1.10% higher CVI in the perifoveal region. Significant mean differences were observed only in the outer temporal subfield (−1.10%, p = 0.005) and outer ring (−0.77%, p = 0.02). No significant scan-pattern effect was found, but CVI varied significantly across the ETDRS grid, with the lowest values in the outer nasal subfield, nasal quadrant and outer ring. Conclusions: Radial scans provide CVI measurements comparable to raster scans, with faster acquisition, supporting practical use in children. Standardising CSI delineation is crucial for consistent CVI comparisons across studies.