Analysis of choroidal structure and vascularity indices with image binarization of swept source optical coherence tomography images: A prospective study of 460 eyes

PURPOSE: To evaluate choroidal vascularity index (CVI) among normal subjects using image binarization of swept source optical coherence tomography (SS-OCT). MATERIALS AND METHODS: Four hundred and sixty eyes of 230 normal participants were included. Total circumscribed choroidal area, luminal area, stromal area (SA), and CVI were derived from SS-OCT scans using open-source software (ImageJ) with the modified Niblack method. Both CVI and subfoveal choroidal thickness (SFCT) were correlated with age, refractive error, intraocular pressure, and mean ocular perfusion pressure (MOPP) using mixed linear model analysis. Pearson's correlation coefficient was used to determine the relationship between age and each dependent factor. Analyses were performed using the SPSS software version 20.0 (IBM Corp., Armonk USA) and statistical significance was tested at 5%. RESULTS: The mean age was 42.1 (±17.6) years. Mean SFCT was 307 ± 79 μm. Mean CVI was 66.80 (±3.8)%. There was statistically significant positive correlation between CVI and increasing age (r = 0.259, P < 0.0001) and statistically significant negative correlation between SFCT and age (r = −0.361, P < 0.0001). There was positive linear correlation between refractive error and CVI (r = 0.220, P < 0.0001) and negative correlation between SFCT and refractive error. There was no significant effect of MOPP on both CVI (P = 0.07) and SFCT (P = 0.7). CONCLUSION: CVI and SFCT are significantly correlated with age and refractive error in normal Indian eyes.