Spatial iris chromaticity disparities as phenotypic correlates of harm avoidance temperament in a Korean sample

Introduction The human iris has a complex developmental origin, with neural crest-derived cells contributing to the formation of the iris stroma and its melanocyte population. Although ocular visual features have been linked to personality traits in Western cohorts, whether quantitative spatial chromaticity disparities in the iris are associated with temperament dimensions in Korean individuals remains understudied. Methods Digital iris images from 100 Korean adults included in the final analytic sample were normalized using Daugman’s rubber-sheet model and partitioned into an eight-subregion polar coordinate grid. Commission Internationale de l’Éclairage L * a * b * chromaticity metrics and spatial disparity indices—directional (superior–inferior, ΔSI; nasal–temporal, ΔNT) and radial (inner–outer, ΔIO)—were extracted along the corresponding color axes. Personality temperaments were assessed using the Korean Temperament and Character Inventory-Revised Short version (K-TCI-RS). Hierarchical regression analysis and 5,000-iteration nonparametric bootstrapping were performed. A Benjamini–Hochberg false discovery rate (FDR) correction was additionally applied across the 12 temperament–chromaticity models as a sensitivity analysis for multiplicity. Results Global mean iris chromaticity parameters were not significantly associated with the examined temperament dimensions. Among the 12 temperament–chromaticity models examined, only the Harm Avoidance (HA)– b * model showed a significant incremental contribution of the spatial disparity block, which was associated with an additional 14.7% of the variance in HA scores (Δ R 2 = 0.147, p = 0.001) and remained statistically significant after FDR correction (FDR-adjusted p = 0.012). Specifically, nasal–temporal disparity (Δ b * NT ; β = −0.210, p = 0.039) was negatively associated with HA, whereas the inner–outer radial gradient (Δ b * IO ; β = 0.291, p = 0.006) showed a positive association. Discussion Among the models examined, spatial iris chromaticity disparities along the yellow–blue ( b *) axis showed an incremental association with HA beyond global mean chromaticity in this Korean sample. These exploratory findings support further investigation of spatial iris colorimetry in relation to temperament and require replication in independent populations.