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Coloboma - External and Internal Eye
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Coloboma - External and Internal Eye

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Contributors: Nitish Mehta MD, Lauren Patty Daskivich MD, MSHS, Brandon D. Ayres MD, Christopher Rapuano MD, Harvey A. Brown MD, Sunir J. Garg MD
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Synopsis

Derived from the Greek word for defect, a coloboma (plural colobomata or colobomas) is a genetic defect resulting from failure of an embryonic structure known as the choroid fissure (also known as the optic or embryonic fissure) to fuse, resulting in a hole in parts of the eye such as the iris, retina, choroid, retina, or optic nerve. Colobomas can be isolated or syndromic and have an extremely varied presentation. They can be found bilaterally or unilaterally and can result in no visual change or severe vision loss, depending on location. They can be cosmetically obvious with no effect on visual acuity when affecting the iris. On the other hand, when located further posteriorly, they may require a dilated ophthalmologic exam for identification and can result in severe vision loss. It is a relatively rare condition, affecting 1:10 000 individuals without racial or ethnic predilection.

The embryonic fissure develops as an invagination of the optic vesicle and leaves a gap inferonasally to allow the entrance of the hyaloid artery. Fusion begins at the equator and then proceeds anteriorly and posteriorly. As such, colobomas are often found inferonasally and either in the anterior structures or posterior structures of the eye. This process is complete by the 5th week of gestation. Other relevant etiologic factors include nutrition and environmental exposure. Rat fetuses made deficient in retinol (Vitamin A) fail to close the optic fissure; this was prevented by supplementing with retinol. Colobomas can also be seen in children with fetal alcohol syndrome. Genetically, the regulation of globe development is complex. Recently, zebra fish deficient in FGF-Ras pathway components have been shown to develop ocular colobomas. Colobomas have been seen to demonstrate autosomal dominant, autosomal recessive, and X-linked inheritance in family studies.

Some syndromes associated with eye colobomas include CHARGE syndrome, cat eye syndrome, Patau syndrome, and Treacher-Collins syndrome. Occasionally, colobomas co-present with microphthalmos, a condition in which one or both eye(s) is abnormally small.

Colobomas of the eyelid are also holes in orbital structures, but arise from failure of fusion of epidermal progenitor cells, not components of the choroid fissure. Colobomas of the upper eyelid in particular can result in severe exposure keratopathy in infants. They can be seen as a component of the Fraser or Goldenhar syndromes.

For more information, see OMIM.

Codes

ICD10CM:
Q13.0 – Coloboma of iris

SNOMEDCT:
92828000 – Coloboma of eye

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Differential Diagnosis & Pitfalls

Conditions appearing similar to iris coloboma:
  • Iris nevi – melanotic macules on iris
  • Iris trauma – classic "teardrop" appearance
  • Aniridia – severe iris tissue hypoplasia
Conditions that can appear similar to optic nerve coloboma:
  • Morning glory disc – large, funneled disc with peripapillary elevation and pigmentation with straight radially exiting retinal vessels reminiscent of a "flower" pattern.
  • Congenital optic pits – herniation of dysplastic retina through defects in the lamina cribrosa resulting in yellowish depression of optic disc, commonly associated with posterior vitreous detachment and serous retinal detachment.
  • Optic nerve staphylomata – defect in sclera near the optic nerve resulting in bowl-shaped excavation of retina and choroid, often atrophic in appearance.
Retinochoroidal colobomata are distinguishable from other causes of leukocoria due to flat, glistening, clearly demarcated white appearance with complete lack of retinal and choroidal tissue. Other causes of white retinal lesions are often raised (retinoblastoma) or have variable pigmentation (infectious scars) or exudate (Coat's disease).

The eyelid coloboma differential includes eyelid trauma and entropion (abnormal inward turning of the eyelid margin).

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Last Updated: 10/31/2018
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Coloboma - External and Internal Eye
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Coloboma : Optic disc atrophy, Pupil shape abnormal, Retinal pigment clumping, Strabismus, Vision loss, Visual field defect
Clinical image of Coloboma
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