coloboma

Coloboma is a congenital eye defect resulting from incomplete closure of the embryonic fissure during early fetal development, typically between the fifth and seventh weeks of gestation. The term derives from a Greek word meaning a notch or mutilation. The defect can affect various ocular structures, most commonly the iris, but also the ciliary body, choroid, retina, or optic nerve. Iris coloboma often creates a characteristic keyhole-shaped pupil, usually located inferonasally.

Types and locations include: iris coloboma (often cosmetic and may not affect vision), iridochoroidal coloboma (involving iris and underlying choroid/retina), chorioretinal coloboma (often associated with more significant visual field loss and higher risk of retinal detachment), and optic nerve coloboma (can cause field defects and reduced vision). Some cases involve multiple structures, and rare eyelid or conjunctival involvement may occur.

Causes and genetics are typically congenital with multifactorial influences. In some individuals, coloboma occurs as part of a syndrome, such as CHARGE syndrome (caused by CHD7 mutations) or renal-coloboma syndrome (PAX2 mutations). Transmission can be sporadic or inherited in autosomal dominant or other patterns depending on the underlying gene. Families with a history of coloboma may be offered genetic counseling and targeted testing.

Clinical features vary with extent. Visual acuity may be normal or reduced, and patients can have field defects, refractive errors, and photophobia. Retinal and choroidal involvement increases the risk of complications such as retinal detachment.

Diagnosis is made by ophthalmologic examination and may include ultrasound or imaging to assess the extent. Management focuses on vision optimization and cosmetic concerns: refractive correction, amblyopia therapy in children, and, in selected iris defects, prosthetic lenses or surgical repair for cosmetic reasons. Monitoring for retinal detachment and addressing associated systemic conditions are important.