A coloboma describes conditions where normal tissue in or around the eye is missing from birth.
Coloboma comes from the Greek word that means “curtailed.” The eye develops quickly during a fetus’ first three months of growth. A gap, known as the choroidal fissure, appears at the bottom of the stalks that eventually form the eye. This fissure generally closes by the seventh week of gestation. If it does not close, a coloboma or space forms.
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, the part of the eye that focuses light onto the retina, is missing.
- Macular coloboma. The macula is the central part of the retina responsible for daylight, fine and color vision. In this coloboma, the macula fails to develop normally.
- Optic nerve coloboma. In this coloboma, the optic nerve, the bundle of fibers that relay light signals to the brain, is hollowed out, reducing vision.
- Uveal coloboma. The uvea is the middle layer of the eye. This coloboma can affect the iris, the colored part of the eye, giving it a distinct keyhole or cat-eye appearance.
- Chorio-retinal coloboma. In this coloboma, part of the retina (the light-sensitive tissue lining the back of the eye) is missing.
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