Accuracy and reliability of artery-vein differentiation in small-field macular OCT angiography

Accurate artery-vein (AV) differentiation in small-field macular optical coherence tomography angiography (OCTA) remains challenging due to a lack of standardized guidelines. We propose and validate criteria for $3\times 3{\mathrm{mm}}^2$ ( $10\mathrm{deg}\times 10\mathrm{deg}$ on Spectralis; $\sim 2.9\times 2.9{\mathrm{mm}}^2$ ) macular scans.

Small field-of-view (FOV) OCTA scans were analyzed using established AV criteria for large-field ( $12\times 12{\mathrm{mm}}^2$ ) OCTA, as applied by two masked readers and validated against color fundus photographs (CFPs) and near-infrared reflectance (NIR) images. Accuracy and reliability (Cohen's $\kappa$ ) were assessed. Pixel-level AV masks were annotated with a standardized threshold. Vessel diameters and intensities were compared within our dataset and in the publicly available OCTA-500 dataset to assess whether intrinsic vessel features support AV differentiation.

A total of 465 vessels from 20 healthy eyes were evaluated across 3 pseudo-branching orders using the criteria for OCTA. Annotators achieved high accuracy (95.1%, 92.3%) and strong intra/inter-rater reliability ( $\kappa =0.84$ ) with similarly high AV classification accuracy within pseudo-third-order vessels (97.15%). No significant AV diameter differences were observed in either dataset ( $p=0.261$ and 0.442). The mean intensity was similar in our dataset ( $p=0.277$ ; $\left|\Delta \right|=3.28$ , 1.45% relative difference) but higher for veins in OCTA-500 ( $p<0.0001$ ; $\left|\Delta \right|=3.42$ , 1.63% relative difference).

Accurate and reproducible AV labeling is feasible in $3\times 3{\mathrm{mm}}^2$ scans, with strong inter- and intra-rater agreement. Vessel diameter and intensity add limited value. NIR-based alignment of OCTA with CFP provides reliable ground truth, supporting consistent manual labeling and OCTA segmentation.