Coloboma, simply put, is a hole in one of the structures of the eye such as the iris, retina, choroid or optic disc. A coloboma can affect one or both eyes. If both eyes are involved, it can affect them the same way or differently. There are different types of coloboma, depending on the part of the eye affected:

• Eyelid coloboma: A piece of the upper or lower eyelid is missing.

• Lens coloboma: A piece of the lens is missing.

• Macular coloboma: The Macula fails to develop normally.

• Optic nerve coloboma: The optic nerve is hollowed out, reducing vision.

• Uveal coloboma: The uvea is the middle layer of the eye. This coloboma can affect the iris, the coloured part of the eye, giving it a distinct keyhole or cat-eye appearance.

• Chorio-retinal coloboma: In this coloboma, part of the retina is missing.

The effects a coloboma has on vision can be mild or more severe depending on the size and location of the gap. If, for example, only a small part of the iris is missing, vision may be normal, whereas if a large part of the retina or optic nerve is missing, vision may be poor and a large part of the visual field may be missing

Coloboma of the iris may be treated in a number of ways. A simple cosmetic solution is a specialized cosmetic contact lens with an artificial pupil aperture. Surgical repair of the iris defect is also possible. Surgeons can close the defect by stitching or by using artificial iris prosthetic devices. This device cannot be used if the natural lens is in place and is not suitable for children. Suture repair is a better option where the lens is still present.

Vision can be improved with glasses, contact lenses or even laser eye surgery but may be limited if the retina is affected or there is amblyopia.