Several developmental eye disorders have a known genetic basis, including microphthalmia and anophthalmia. Anophthalmia is the complete absence of the globe, or bulb, of the eye and hence the most severe structural eye malformation. A milder form is microphthalmia, where the total axial length of the eye globe is at least two standard deviations below the mean for age. Simple microphthalmos refers to a structurally normal eye with short total axial length. In each of these conditions, the eyelids, conjunctiva and lacrimal apparatus are normal. In complex microphthalmia, additional abnormalities are present and may include anterior segment dysgenesis, cataract, persistent hyperplastic primary vitreous, chorioretinal coloboma and/or retinal dysplasia. Anophthalmia/microphthalmia has been observed in association with various genetic syndromes and approximately 25% of individuals with anophthalmia/microphthalmia have identifiable chromosomal abnormalities (Forrester 2006). Mutations in the SOX2, OTX2, SIX6 and VSX2 genes leading to haploinsufficiency may be associated with anophthalmia and microphthalmia. SOX2 mutations are also known to be associated with hearing loss, developmental delay, esophageal atresia, genitourinary abnormalities, myopathy, and spastic diplegia. OTX2 mutations have been reported in patients with anophthalmia/microphthalmia associated with brain malformations and pituitary insufficiency. VSX2 mutations are usually associated with isolated ocular finding without other systemic malformations. Heterozygous deletions of the entire SIX6 gene have been seen in some cases of bilateral anophthalmia due to interstitial chromosome deletions. PAX6 mutations have also been associated with anophthalmia (analysis of PAX6 is available, for further information see http://www.genedx.com).