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Coloboma
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Coloboma

Coloboma is a congenital eye abnormality where missing tissue in eye structures creates gaps or notches, potentially impacting vision.

Overview

Coloboma is an eye abnormality that occurs before birth, characterized by missing pieces of tissue in structures that form the eye. These gaps may appear in the iris (the colored part of the eye), the retina (light-sensitive tissue at the back of the eye), the choroid (blood vessel layer under the retina), or the optic nerve. Depending on the size and location, colobomas can cause vision loss. Some individuals also have microphthalmia, where one or both eyeballs are abnormally small.

Symptoms

The impact of coloboma varies significantly based on the affected structure:

  • Iris coloboma: Often results in a "keyhole" pupil appearance and generally does not cause vision loss.
  • Retinal/Optic nerve coloboma: Can cause vision loss in specific parts of the visual field or low vision that cannot be corrected with glasses or contacts.
  • Associated conditions: May include cataracts (clouding of the lens), glaucoma (increased eye pressure), nearsightedness, nystagmus (involuntary eye movements), or retinal detachment.

Causes

Coloboma arises from the incomplete closure of the optic fissure (also known as the choroidal or embryonic fissure) during the second month of fetal development. Because this fissure forms at the bottom of the eyeball, colobomas typically occur in the lower half of the eye. The condition can be caused by various genetic changes or chromosomal abnormalities. Environmental factors, such as prenatal alcohol exposure, may also increase the risk of developing coloboma.

Inheritance

Isolated coloboma is most often not inherited, though it can be passed down through families. Inheritance patterns can include:

  • Autosomal dominant: One copy of an altered gene is sufficient to cause the disorder.
  • Autosomal recessive: Both copies of a gene must have mutations.
  • X-linked: The gene is located on the X chromosome, which can follow X-linked dominant or X-linked recessive patterns.

When coloboma occurs as part of a syndrome, it follows the inheritance pattern associated with that specific condition.

Frequently Asked Questions

Iris colobomas usually produce a “keyhole” pupil but rarely impair vision. If visual acuity is affected, corrective lenses or contact lenses may help. In rare cases where the coloboma causes significant glare or light sensitivity, surgical patching or laser therapy can be considered.
Retinal or optic nerve colobomas can predispose to retinal detachment, cataracts, glaucoma, and localized visual field loss. Regular comprehensive eye exams every 6–12 months, including dilated fundus examinations and intraocular pressure checks, are recommended to catch complications early.
Genetic counseling and testing can be useful, especially if the family history suggests an autosomal dominant pattern. Genes such as PAX2, CHD7, and RAX are frequently implicated. A targeted panel can identify pathogenic variants, helping to assess recurrence risk and guide surveillance for associated conditions.
Coloboma can sometimes be identified on prenatal ultrasound if the defect is large, but many cases are only noticed after birth during a routine eye exam. Newborns with family history or other congenital anomalies should receive an early ophthalmologic assessment to rule out coloboma.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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