Optic Nerve Coloboma

Excerpt

The term coloboma derives from the Greek word koloboma, originally used to indicate a part that was removed by mutilation, missing or cut short. Colobomas are congenital ocular defects that can affect the iris, the lens, the choroid, the retina, and the optic nerve.

Eyelid colobomas result in a full-thickness defect of the eyelid: although the coloboma may occur anywhere on the eyelids, the most common site is at the junction of the medial and middle third of the upper eyelid. Eyelid colobomas are classified as traumatic (accidents, surgery) or congenital. Congenital colobomas may be isolated or may occur in the presence of other facial deformities and syndromes. In eyelid colobomas, corneal protection is paramount. Topical lubricating drops and ointment are applied and moisturizing chambers may be used. Patching is sometimes necessary. Surgical repair to improve corneal coverage is undertaken as necessary. The size and location of the defect will determine the exact surgical procedure used. Direct closure may be performed in defects up to 25% of the eyelid. In defects larger than 25% and up to as much as 60%, lateral mobilization with canthotomy, cantholysis and multiple “Z” plasties allows direct closure of the coloboma. When the defect is larger, lid-sharing procedures like the Hughes procedure for lower lid reconstruction and the Cutler-Beard procedure for upper eyelid closure may be necessary, together with the use of skin grafts.

Iris colobomas affect the infero-nasal quadrant and are caused by failure of the embryologic optic fissure to close during the fifth gestational week. This results in a typical keyhole-shaped pupil. On occasion, a bridge of iris may be present in the coloboma, giving rise to type of coloboma called a "bridge coloboma". Iris colobomas are frequently bilateral and associated with a pyriform corneal shape. When the corneal shape is normal, one must look for a surgical cause of a coloboma.

Iris colobomas may be associated with colobomas of the ciliary body, choroid, retina or optic nerve. Glaucoma, nystagmus, or strabismus may be seen in the presence of iris colobomas.

Iris colobomas may cause photophobia, visual distortion and double vision. They may also be cosmetically unacceptable. Cosmetic contact lenses with an artificial pupil may be used. Surgical repair of the defect with sutures may be possible. Artificial iris prosthetic devices are being explored in the presence of pseudophakia. Iris-painted intraocular lenses may be implanted after removal of the cataract. Foldable artificial irises may also be inserted through a small incision

Management of associated findings: limbal dermoids may appear simple but care should be taken as penetration into the globe is a very real risk. No such resection should be undertaken without availability of a lamellar graft (cornea or sclera or both).

The rest of this article discusses optic nerve colobomas.