A coloboma is a congenital defect in the structure of either the eyelid or the eye [See figure 1].
Coloboma can be inherited or can occur spontaneously.
Coloboma of any eye structure can occur in isolation or it 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).
Coloboma may involve the iris, lens, retina, or optic nerve. The embryonic fissure normally closes around the 5th week of gestation (during pregnancy). Improper closure of the fissure causes a defect (coloboma) in one or more of the eye structures.
It is a defect which varies from a small notch to near total absence of the eyelid. It most commonly affects the upper 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. Another syndrome that may be associated with coloboma of the lower lid is Treacher Collins syndrome, which is characterized by depressed cheeks, slanted appearance of eye, and a small mandible.
The lid defect will leave part of the cornea uncovered, which can lead to excessive dryness due to evaporation of the tears.
The eye usually requires extra lubrication to prevent drying of the surface, and eventually may require surgery to close the defect.
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.
A small or large developmental defect may occur in the deeper structures of one or both eyes[See figure 3]. The defect can involve the retina (layer lining the back of the eye responsible for sight) and/or the optic nerve (which connects the eye to the brain). The eye is occasionally smaller than normal.
If the defect extends to the central part of the retina or optic nerve, vision can be impaired, sometimes severely.
The most common symptom is noticing a defect in the iris (iris coloboma), a small eye, or poor vision. A coloboma of the retina or the optic nerve can only be seen when the back of the eye is examined by an ophthalmoscope.
Detachment of the retina can occur any time in life. Regular follow up is important to detect detachment and treat it early.
Incomplete embryonic fissure closure produces a cyst outside the eye, attached to a very small eye.
An optic nerve pit may be related to coloboma and is a small defect near the margin of the optic nerve. Fluid can sometimes collect in the retina adjacent to the defect which may cause reduced vision
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