colobomas

Coloboma is a congenital defect of the eye caused by incomplete closure of the embryonic fissure during early development, typically between weeks 5 and 7 of gestation. The defect can affect different ocular structures, most commonly the iris, but it can involve the choroid, retina, ciliary body, or optic nerve. Iris colobomas produce a characteristic keyhole or notch in the pupil and are usually inferonasally located. Posterior segment colobomas (retinochoroidal or optic nerve colobomas) occur in the back of the eye and can involve extensive retinal or choroidal tissue.

Etiology and associations: Coloboma can be isolated or part of a syndrome. It may have genetic causes, with associations to genes such as PAX2, CHD7, and others, and to syndromes including CHARGE syndrome. Environmental factors during development can also contribute. Colobomas may be unilateral or bilateral.

Clinical features and prognosis: The impact on vision depends on the size and location of the defect. Iris colobomas may cause little visual impairment but can be associated with glare or anisometropia. Posterior segment colobomas can cause reduced vision, scotomas, or an increased risk of retinal detachment. Coloboma can be part of broader ocular or systemic findings, influencing prognosis.

Diagnosis and management: Diagnosis is by ophthalmic examination, with slit-lamp biomicroscopy for anterior segment lesions and dilated fundus examination or ultrasonography for posterior defects. Genetic testing and counseling are considered in familial or syndromic cases. Management focuses on optimizing vision and monitoring for complications: refractive correction, cosmetic or prosthetic options for iris defects, and surveillance for retinal detachment or glaucoma. Visual prognosis is highly variable and depends on the extent and associated conditions.