Distribution of Choroidal Thickness and Choroidal Vessel Dilation in Healthy Japanese Individuals: The Nagahama Study.

Purpose: To report fundamental epidemiologic data for choroidal parameters such as choroidal thickness and index of choroidal vascularity in Japanese individuals and to evaluate their correlations with age, sex, systemic parameters, and other ocular parameters. Design: Population-based cohort study. Participants: A total of 9850 individuals participated in the first follow-up of the Nagahama Prospective Cohort for Comprehensive Human Bioscience (the Nagahama Study) conducted between 2013 and 2016. Methods: All participants underwent standardized ophthalmic examinations, including OCT with enhanced depth imaging (EDI; RS-3000 Advance; Nidek). We manually segmented the choroidoscleral interface to measure subfoveal choroidal thickness (SFCT) and calculated the normalized choroidal intensity obtained with EDI (NCIEDI) and choroidal vascularity index (CVI). These are indices of choroidal brightness in OCT and reportedly represent the dilation of choroidal vessels. After summarizing the age-sex stratified distributions of SFCT, NCIEDI, and CVI, their associations with age, sex, axial length (AL), and spherical equivalent (SE) were evaluated using linear regression analysis with adjustments for possible confounders. Main Outcome Measures: Distribution of SFCT, NCIEDI, and CVI in the healthy Japanese population and their characteristics. Results: Age-sex standardized SFCT, NCIEDI, and CVI were 291.2 µm, 0.653, and 66.88%, respectively. In both men and women, SFCT was associated negatively with age (P < 0.001) and NCIEDI was associated positively with age (P < 0.001). Although both SFCT and NCIEDI did not differ significantly between men and women overall (P = 0.87 and P = 0.21, respectively), among younger participants (35-50 years of age), men showed significantly greater SFCT than women (P < 0.001). Only in men was CVI associated positively with age (P < 0.001). In the multivariable analysis, SFCT was associated significantly with age, sex, AL, SE, and the interaction term of age and sex (P < 0.001). Independent of SFCT, NCIEDI and CVI were associated significantly with age (P < 0.001). Conclusions: We report normative Japanese SFCT, NCIEDI, and CVI data using a large general Japanese cohort. The association analysis of SFCT with NCIEDI and CVI suggested that younger individuals have a more lumen-rich choroid for their choroidal thickness than older individuals.