OTX2 and Anophthalmia: Homozygous mouse knockouts of homeobox gene Otx2 lack eyes, while heterozygous knockout mouse models also show a highly variable phenotype, from acephaly, micrognathia, anophthalmia, microphthalmia to normal development, depending on the genetic background [8,25,63,80,215,216,217,218,219].