Coloboma

What is Coloboma?

• The eyelid is the eye's first line of defence and when danger is sensed the lids automatically close.
• The iris forms a pigmented curtain dividing the cornea and the lens and gives colour to the eye as well as controlling the amount of light entering the eye, by varying the size of the pupil.
• The lens is the transparent intraocular tissue forming the natural lens of the eye, helping to bring rays of light to focus on the retina.
• The retina is located at the back of the eye and forms a light-sensitive screen made up of several cell layers. When light reaches the retina it is converted to nerve impulses which transmit the information to the brain.
• The choroid provides essential nourishment to the retina through its thin network of blood vessels.
• The optic disc is the exit site from the eye of retinal nerve fibres, which carry the impulses for sight from the retina via the optic nerve to the brain.

What causes Coloboma?
Although no specific pattern has been identified there appears to be a strong hereditary factor in the incidence of this condition, which is sometimes linked to chromosomal disorders.

During the first three months of pregnancy, the eyes of the foetus are developing quickly, starting as a small bud which then sprouts out so that all the intricate parts of the inside of the eye can be formed and nourished. To aid this nourishment a gap, known as the foetal cleft, opens on the underside of each bud.

When the intricate development of the eye is completed, the gap closes but in some cases the gap either does not close or closes only partially and such gaps will remain throughout life. This gap is Coloboma. This does not mean that there is a hole in the eye, just that certain structures within the eye do not fully form.

What are the effects of Coloboma?
The effects of the condition can be mild or severe and this will depend upon the extent and location of the gap (or incomplete closure). The gap is usually at the bottom of the eye. Coloboma may occur in one or all of the structures listed above

A lens coloboma, if large, may also include flaws in the iris and choroid and slightly increase risk of retinal tearing. In severe cases, the eye may be reduced in size. This condition is called Microphthalmia, a condition that may arise without coloboma.

Coloboma of the iris may sometimes gives a keyhole shape to the pupil. Central vision may be affected and may reflect the extent, location and shape of the gap. In some cases the problem may be accompanied by other problems in the body which may be neurological or chromosomal. A few rare syndromes also include coloboma among their potential problems.