There are numerous causes of ONH, with most cases arising from genetic abnormalities in patients. Mutations in a variety of genes, including the following, result in hypoplasia of the optic nerve: NR2F1, OTX2, VAX1, ATOH7. In addition to genetic factors, other causative factors have been suggested, including exposure to various infections during pregnancy and endocrinological abnormalities during development. With respect to SOD, as previously eluded to earlier, the condition arises from abnormalities during embryological development. The exact cause of SOD is poorly understood; although it is likely genetic factors play an important role, with various patients exhibiting mutations in the genes HESX1, OTX2, and PAX6. In addition, exposure to certain medications is thought to play an important role in the development of SOD.