The condition is likely to occur because the delicate sequence of early developmental steps to form the eye is disrupted in some way. This could be because of changes in genes or through external factors acting on the developmental processes during pregnancy or a combination of the two. Anophthalmia and microphthalmia have been related to some illnesses during pregnancy such as rubella and chicken pox. They have also been linked to some drugs taken during pregnancy, including recreational drugs and thalidomide.
Over the last few years, several genes have been described as important in anophthalmia and microphthalmia. These eye development genes include SOX2, OTX2, BMP4, RX, SHH (sonic hedgehog), CHX10 (also called VSX2), BCOR, BMP7, RAB3GAP, FOXE3, PITX2, FOXC1, MITF, HCCS, CHD7, CRYBA4, GDF6, LRP6, STRA6 and PAX6. Whilst many of these genes have only been described so far in association with a few families worldwide, SOX2 seems to be important in around 10-15 per cent of children with anophthalmia.