Quantitative measurement of Iris melanin concentration by polarization-sensitive anterior segment optical coherence tomography

Purpose: This study aimed to evaluate iris melanin concentration using polarization-sensitive anterior segment optical coherence tomography (PS-AS-OCT) and to explore its correlation with iris color in individuals with brown irides. Methods: Iris cross-sectional images were acquired using PS-AS-OCT. Substructural layers were automatically segmented using a deep learning model. The melanin concentration ratio (MCR) was derived from entropy-based PSAS-OCT images to quantify melanin within the iris layers. Iris surface color was analyzed using CIE L*a*b* values from high-resolution photographs. Correlation analyses were performed between MCR and L*a*b* values. Additionally, a three-grade iris color classification was used, and K-nearest neighbors (KNN) modeling assessed the predictive value of MCR. Results: Eighty-eight participants (mean age: 39 years) were included. MCR of the iris stroma showed a strong negative correlation with iris color: L* (r = 0.72), a* (r = –0.56), and b* (r = –0.68), all P < 0.001. Stromal MCR significantly differed among color grades (P < 0.001), and the KNN model achieved 85% classification accuracy. Conclusions: PS-AS-OCT–derived stromal MCR is strongly associated with iris color and offers a noninvasive approach for evaluating iris melanin. This technique may provide new insights into ocular pigmentation.