Close regulation of PAX6 expression is required throughout embryogenesis to ensure normal development; underexpression results in the aniridia spectrum of iris, foveal and optic nerve hypoplasia with associated glaucoma, cataracts and keratopathy, whilst overexpression causes microphthalmia, microcornea and ciliary body maldevelopment [79,80,81]. Here, PAX6 is linked to microphthalmia.