CYP4V2 and Bietti crystalline dystrophy: Comparing the distribution of disease-causing genes in our cohort to those of data from similar studies in China and the US13,20, we found that all three cohorts shared some common disease-causing genes such as EYS, USH2A, ABCA4, RPGR, PRPF31, and CEP290. Some genes, such as PROM1 associated with RP, CRD, and Stargardt disease, as well as CYP4V2 associated with Bietti crystalline dystrophy, were frequently found in our cohort and the cohort from China but were less frequent in the US cohort.