Developmental defect is caused by defective closure of the embryonal fissure. Its effect on vision varies depending on the size and location of the defect (1).
In children, colobomas are associated with other significant comorbid conditions. Specifically, 80–90% of children diagnosed with CHARGE (acronym for a group of developmental abnormalities) have a coloboma.
Pregnant mothers with a coloboma have a slightly increased risk of having children with a coloboma, but the condition has not proven to be fatal.
Rare condition occurring in only 0.14% of the general population
Estimated prevalence of coloboma (all types) is 1 per 10,000. More specific epidemiology for choroidal coloboma is not currently available (2).
Risk factors for colobomas include consanguineous parents, positive family history, vitamin A deficiency, and second-born child.
• Can be associated with mutations in the PAX-2 gene as part of the renal-coloboma syndrome (3).
• An irregular autosomal dominant inheritance pattern is found in many of these patients.
A typically bilateral birth defect resulting from failed closure of the embryonic optic fissure/cup, during the 6th week of gestation
Unknown. It is postulated that a genetic predisposition is the underlying cause.
COMMONLY ASSOCIATED CONDITIONS
• Iris coloboma
• Retinal detachment
• Lens coloboma
• Optic pit
• Various systemic birth defects:
– It is often found in several congenital syndromes, including CHARGE syndrome (Goldenhar, Schmid–Fraccaro, Joubert, Mohr-Clausen, and Aicardi syndromes).
• The effects on vision differ depending on the size and location of the coloboma.
• Is there a change in vision?
• Does the patient notice visual field loss?
• If the vision loss or peripheral field loss is recent, there may be a recent retinal detachment.
• Are other family members affected?
• Is there any history of renal, genitourinary, growth, palate, or hearing difficulties?
• As there may be malformations in other parts of the body (CHARGE syndrome), patients should be checked for coloboma of the eye, heart defects, atresia of the nasal choanae, retardation of growth, genitourinary abnormalities, and ear abnormalities.
• Findings on funduscopic exam may range from very mild, small white lesions on the inferior optic disc to a large defect, which extends from the optic disc to the anterior segment.
• Rarely, a normal portion of the fundus is located between the defects (“bridge” coloboma).
• Patients may have a coexisting iris coloboma (which is what prompted the initial visit to the ophthalmologist).
DIAGNOSTIC TESTS & INTERPRETATION
None is generally necessary as it is a clinical diagnosis.
• Funduscopic and complete physical examination typically elicits the features of choroidal coloboma.
• B-scan ultrasonography and/or CT scan (none usually needed) can be used to show a small, disorganized globe (microphthalmia) with a retroocular cyst that is connected to the vitreous humor inferiorly.
• Neuroimaging can be used to elicit midline developmental defects.
• Optical coherence tomography can demonstrate the transition from normal retina to intercalary membrane and subretinal fluid (4)[C].
• The choroidal coloboma shows an absence or atrophy of choroid and an absence of retinal pigment epithelium (RPE) with atrophic and gliotic retina:
– The RPE tends to be hyperplastic at the edge of the defect.
– The sclera in the region is usually thinned and may be cystic; the cystic space is often filled with proliferated glial tissue.
• Chorioretinal scar
• Aicardi’s syndrome
• Goldenhar syndrome
• North carolina macular dystrophy
• Consider systemic evaluation for chromosomal abnormality
• Treatment of refractive error and amblyopia, if present
• Low Vision (vision rehabilitation) services, if indicated
If a patient develops a rhegmatogenous retinal detachment, vitrectomy with laser and intraocular gas or silicone oil tamponade is indicated.
Patients will need periodic follow-up with a retina specialist and/or pediatric ophthalmologist.
• Foveal involvement is an important predictor of visual acuity.
• Even patients with very large colobomas may have good vision is the macular architecture is normal.
• Refractive error
• Choroidal neovascularization
• Retinal detachment (later in life)
1. Schubert H. Structural organization of choroidal colobomas of young and adult patients and mechanism of retinal detachment. Trans Am Ophthalmol Soc 2005;103:457–472.
2. Schubert HD. Choroidal coloboma. Ophthalmology 2007;114(12):2369.
3. Eccles MR, Schimmenti LA. Renal-coloboma syndrome: A multi-system developmental disorder caused by PAX2 mutations. Clin Genet 1999;56:1–9.
4. Gopal L. A clinical and optical coherence tomography study of choroidal colobomas. Curr Opin Ophthalmol 2008;19:249–254.