Coloboma

A congenital gap or defect in an eye structure, usually caused by incomplete closure of the embryonic optic fissure. Its effects depend on which structures are involved and how extensive the defect is.

Optic fissure: A temporary opening along the developing optic cup that allows blood vessels to enter the embryonic eye. Incomplete closure of this opening is the usual developmental cause of coloboma.
Choroidal coloboma: A congenital defect in the choroid, the vascular layer between the retina and sclera. It names coloboma when the choroid is involved.
Visual field: The full area visible to an eye while it remains fixed on a point. A retinal or optic nerve coloboma can create field defects corresponding to missing tissue.
PAX2: A developmental gene that encodes a transcription factor involved in kidney and optic nerve formation. Pathogenic variants can cause optic nerve coloboma as part of renal-coloboma syndrome.
Aniridia: A congenital or acquired condition involving partial or near-total absence of the iris. Both can alter the pupil's appearance, but aniridia usually reflects a broader iris-development defect.
Optic cup: The double-walled embryonic structure that develops into the retina and retinal pigment epithelium. The optic fissure forms in its lower region during early eye development.
Retinal coloboma: A congenital absence or malformation of retinal tissue, commonly associated with optic fissure closure failure. Retinal involvement can affect vision even when the iris looks normal.
Amblyopia: Reduced vision in an eye that did not develop normal visual function during childhood. Unequal vision or associated refractive errors can lead to amblyopia in affected children.
CHD7: A gene encoding a chromatin-remodeling protein; pathogenic variants cause most cases of CHARGE syndrome. CHD7-related CHARGE syndrome commonly includes coloboma.
Iris hypoplasia: Underdevelopment of the iris that leaves it thin or structurally incomplete. It can resemble iris coloboma without forming the characteristic localized gap.

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