CYP4V2 and Bietti crystalline dystrophy: In a 2021 cohort study in Taiwan, IRD cases were identified to be a genetic-related disease in 57.1% of the recruited population, with ATP-binding-cassette-subfamily-a-member-4 (ABCA4) variants being the most common at 15.2% and cytochrome-P450-family-4-subfamily-V-member-2 (CYP4V2) variants the most abundant cause of single phenotype (3.8% Bietti’s crystalline dystrophy).