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Coloboma

What is a coloboma?

A coloboma is a congenital defect in the structure of either the eyelid or the eye [See figure 1].

Is coloboma heritable?

Coloboma can be inherited or occur spontaneously. Some family members have severe loss of vision while others see well.

What medical problems are associated with coloboma?

Coloboma can occur in isolation. It also can occur with chromosomal abnormalities that involve other body structures. Coloboma can occur in conjunction with heart defects, choanal atresia, nervous system abnormalities, genital or urinary tract anomalies or ear malformations (CHARGE syndrome).

Fig. 1 Coloboma is a congenital defect in the structure of either the eyelid or the eye.

What is a coloboma of the eyelid?

It is a defect (more commonly the upper eyelid) which varies from a small notch to near total absence of the eyelid.

What other abnormalities occur with a coloboma of the eyelid?

Eyelid coloboma can be associated with Goldenhar syndrome, which is characterized by a growth on the eye (limbal dermoid), abnormal eye movement (Duane syndrome), ear abnormalities, or vertebral abnormalities.

How is a coloboma of the eyelid treated?

The eye usually requires extra lubrication to prevent drying of the surface, and eventually surgery may be required to close the defect.

What types of colobomas occur in the eye?

The embryonic fissure normally closes around the 5th week of gestation (during pregnancy). Improper closure of the fissure causes a defect (coloboma) in the structure of the iris, lens, retina, or optic nerve.

Fig. 2 Iris coloboma.

What is an iris coloboma?

Iris coloboma is a defect in the lower aspect of the colored part of the eye. The pupil is round above and elongated below making an old-fashoined "keyhole" shape [See figure 2]. All children with iris coloboma should have a complete eye exam by an ophthalmologist to look for structural defects inside the eye.

Does iris coloboma affect vision?

If no other abnormalities are present, vision may be normal. Some increase in light sensitivity may occur because of a larger pupil. Contact lenses that change eye color can be used to cover the iris coloboma.

Fig. 3 Fundus or optic nerve coloboma.

What is a fundus or optic nerve coloboma?

A small or large developmental defect may occur in the deeper structures of the eye or eyes. The defect can involve the retina (layer of nerves responsible for sight) and/or optic nerve (connects the eye to the brain). Coloboma of the central retina or optic nerve can reduce vision, sometimes severely. The eye is occasionally smaller than normal [See figure 3].

Does a coloboma inside the eye affect vision?

If the coloboma involves the optic nerve or large areas of the retina, vision may be reduced. Depending on the extent of involvement, this varies from mild to severe reduction in vision.

What are the signs of coloboma?

The most common signs are a defect in the iris (iris coloboma), a small eye, or poor vision.

What is a colobomatous cyst?

Incomplete embryonic fissure closure produces a cyst outside the eye, attached to a very small eye.

What is an optic nerve pit?

An optic nerve pit may be related to coloboma and is a small defect near the margin of the optic nerve. Vision may be reduced if fluid collects in the retina adjacent to the defect.