Definition
One speaks of a coloboma in the general sense of the word when there is a cleft in the eye. The iris (iris) is most frequently affected. When looking closely into the eye, a “keyhole-shaped” pupil can be seen in affected individuals.
This is the round pupil and a dark slit through which one also looks into the eye. At this point the iris has not closed completely. More rarely, other structures of the eye can also be affected. This can lead to a coloboma of the eyelid and the lens. Also the posterior segment of the eye (fundus and papilla = place where the optic nerve enters the eye) can be affected.
What are the causes of coloboma?
A coloboma on the eye is congenital in most cases. In the embryonic phase, a defect in the development of the eye occurs. Mutations in various genes often play a role in this.
More rarely, environmental factors are involved. They are of particular importance in the 4th to 15th week of pregnancy, as it is during this period that the structure of the eye develops. If there are strong external influences during this phase, this can disturb the development of the eye.
In principle, a coloboma can be present in only one or both eyes. It is not possible to separate exactly which causes play a role in the bilateral and which in the unilateral development of the coloboma. Furthermore, the development of a coloboma in the eye is associated with other malformations and diseases.
Frequently, syndromes lead to malformations of the face and skull, and the eye may also be affected. Hereditary diseases that can trigger a coloboma in the eye are, for example, trisomies, in which a chromosome (structure on which part of the human genetic material is stored) is present in triplicate (instead of in duplicate as is normally the case). The best known trisomy is trisomy 21 (also called Down syndrome).
However, other genetic diseases such as the CHARGE association or the DiGeorge syndrome can also lead to colobomas of the eye, among other malformations. In principle, a coloboma of the eye can also only develop in the course of life. Typically, this can occur after injuries to the eye or operations that do not heal completely. Such a coloboma is usually only present on one side.
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