Nine studies examined the role of 19 polymorphisms of 6 dopaminergic genes in BED: DRD2 [15,24,25,26,27], ANKK1 27,28, OPRM1 [26], COMT [17,29], DAT1 [15,16], and DRD3 [15]. This evidence concerns the gene OPRM1 and X-linked cone dysfunction syndrome with myopia.