Coloboma

A coloboma is a condition in which there is a defect in the normal anatomy of the eye.

Structures that may be involved in this condition include the iris, ciliary body, retina, choroid and disc. The condition is caused by the incomplete closure of the embryonic tissue through which the vascular supply reaches the developing eye and the nerve fibres from the retina which leave it.

If the iris and ciliary body are involved the defect is usually positioned downwards and inwards. In this case the iris has a notch extending back into the ciliary body so that the pupil becomes oval or pear-shaped.

A coloboma of the retina and choroid is in the lower half of the eye and varies in size. In this circumstance the white sclera is visible where the overlying retina and choroid are absent. The defect is often continuous with the disc but may be isolated from it. Occasionally it may be confused with an old inactive choroiditis. However the pigmentary changes associated with the inflammatory lesion are often absent with the coloboma.

A coloboma may involve the disc.

Visual acuity is often affected if there are large defects in the fundus.