Coloboma: An Overview

Reuben Oza

Introduction

A coloboma is a congenital defect which occurs due to incomplete closure of the optic fissure, which normally occurs between the fifth and seventh week of foetal development (1,2). The resultant effect is a ‘hole’ within an area of ocular tissue, and can affect the optic nerve, macula, choroid/retina, ciliary body, uvea, iris, lens or eyelids (3).

Epidemiology and Associated Conditions

Globally, approximately one out of ten thousand babies each year are born with a coloboma, with colobomas affecting the iris being most common (4). Whilst colobomas can occur sporadically, for example due to in-utero environmental factors such as maternal alcohol or recreational drug use, they can also occur secondary to genetic mutations, in which case they are typically associated with systemic conditions. Examples of associated genetic conditions include CHARGE syndrome, DiGeorge syndrome, Edwards’ syndrome and Patau’s syndrome (5).

Clinical Features

Characteristically, colobomas affect the tissue’s inferonasal quadrant, and if found in another region, they are termed ‘atypical’ (6). Patients may have varying presentations, with some being asymptomatic, whilst others experience reduced visual acuity, photophobia and/or diplopia (4). Colobomas are also commonly associated with cataracts and/or glaucoma (3). With the commonest type of coloboma which affects the iris, the characteristic clinical feature is described as a “keyhole” sign, caused by incomplete closure of the iris inferiorly (6).

Diagnosis

As with all patients who present to a clinician, the diagnostic pathway is largely formed by history and examination. Eliciting the above visual symptoms, and assessment of visual acuity and visual fields, alongside retinochoroid examination using ophthalmoscopy, and the anterior segment of the eye using slit-lamp forms the bulk of diagnosis (7). As colobomas may occur secondary to inherited mutations, it is often useful to examine the parents’ eyes and consider chromosomal analysis (7). Note however, due to varying levels of penetrance, parental phenotypes may differ from the underlying genotype (5).

Management

Management largely centres around symptom-management, for example corrective lenses if experiencing refractive error, eye-patches if there is a danger of amblyopia, low vision aids and providing information to parents. In patients with colobomas affecting the eyelids, oculoplastic surgery to protect the cornea via lid reconstruction can be effective. Patients with retinochoroidal colobomas are at an increased risk of retinal detachment, and so benefit from regular follow-up, and prophylactic treatment if indicated (6).

References

  1. American Association for Pediatric Ophthalmology and Strabismus. Genetic disorders clinical update: coloboma [Internet]. Roseville (MN): AAPOS; [updated 2024; cited 2025 Jul 17]. Available from: https://aapos.org/patient/patient-resources/genetic-info-patients/genetic-disorders-clinical-update-coloboma
  2. Azzam D, Bordoni B. Embryology, optic fissure. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Mar 3 [cited 2025 Jul 17]. Available from: https://pubmed.ncbi.nlm.nih.gov/32119320/
  3. National Eye Institute. Coloboma [Internet]. Bethesda (MD): National Eye Institute, National Institutes of Health; [updated Dec 6 2024; cited 2025 Jul 23]. Available from: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/coloboma
  4. Cleveland Clinic. Coloboma [Internet]. Cleveland (OH): Cleveland Clinic; [updated 27 Dec 2022; cited 2025 Jul 23]. Available from: https://my.clevelandclinic.org/health/diseases/22682-coloboma
  5. Gopal L, Sen AC, Lingam V, Bhende M, Padhi TR, Xinyi S. Ocular coloboma—a comprehensive review for the clinician. Eye (Lond). 2021 Mar 21; 35(8): 2086–2109. Available from: https://doi.org/10.1038/s41433-021-01501-5
  6. Herren DJ, Mawn LA. Coloboma. EyeWiki [Internet]. San Francisco (CA): American Academy of Ophthalmology; [updated 2025 Jun 8; cited 2025 Jul 17]. Available from: https://eyewiki.org/Coloboma
  7. Tidy C. Coloboma. Patient [Internet]. 2023 Jun 12 [cited 2025 Jul 17]. Available from: https://patient.info/doctor/coloboma

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