CYP4V2 and Bietti crystalline dystrophy: The probable reasons for the inability to identify a variation in CYP4V2 are: (i) the variation might have occurred in the promoter region of CYP4V2; (ii) it could be a heterogeneous disease in which additional genes of lipid metabolism are involved; and (iii) the disease pattern we have seen in two patients with CNV in our cohort simulates a phenotype similar to BCD.