What is coloboma? | Symptoms, causes & treatment

Coloboma is a congenital defect caused by incomplete closure of the embryonic fissure, resulting in a missing piece of ocular tissue that may involve the iris, lens, ciliary body, choroid, retina, optic nerve, or eyelid. Symptoms depend on location and include photophobia, decreased vision, visual field loss, and cosmetic concerns. Diagnosis is clinical with dilated fundus examination and adjunctive imaging (optical coherence tomography, ultrasound) plus genetic and systemic evaluation when indicated. Management targets refractive correction, amblyopia therapy, protection from light and exposure, low vision rehabilitation, and complication control; surgery is reserved for selected iris, eyelid, cataract, and retinal detachment cases.

Key Points

• Coloboma results from failure of the fetal fissure to close (5–7 weeks gestation) and can affect anterior or posterior ocular structures in a typical inferonasal distribution.
• Visual prognosis is primarily determined by macular and optic nerve involvement; isolated iris coloboma often spares acuity but causes photophobia and cosmetic issues.
• Posterior coloboma carries a lifelong risk of retinal detachment; prophylactic laser to the coloboma margin is used by some clinicians, but high-quality evidence is limited.
• Evaluate for associated ocular anomalies (microphthalmia, cataract, glaucoma, strabismus) and for syndromic disease (notably CHARGE); consider genetic testing and systemic workup.
• Treatment emphasizes refractive correction, amblyopia therapy in children, tinted/prosthetic contact lenses for light sensitivity, protection from exposure, and timely management of complications.
• Eyelid coloboma requires corneal protection and surgical repair; large defects are repaired early to prevent exposure keratopathy.

Anatomy and Physiology

Closure of the embryonic (choroidal) fissure proceeds from central to peripheral in the ventral globe and optic stalk between weeks 5 and 7 of gestation. Failure of closure leaves tissue gaps corresponding to the developing structures:

• Iris stroma and sphincter (anterior segment)
• Lens equator and zonules
• Ciliary body
• Choroid and retinal pigment epithelium (RPE)
• Neural retina
• Optic nerve head and peripapillary tissues Eyelid coloboma arises from defective eyelid fold fusion and is embryologically distinct from ocular fissure non-closure.

Etiology

• Developmental: Primary failure of embryonic fissure closure.
• Genetic: Heterogeneous. Pathogenic variants reported in PAX2 (renal coloboma syndrome), PAX6, CHD7 (CHARGE syndrome), SHH, MAF, RAX, SOX2, VSX2, among others [1–4]. Inheritance may be autosomal dominant, autosomal recessive, X-linked, or sporadic; penetrance is variable.
• Environmental/teratogenic associations: Maternal exposure to retinoic acid (isotretinoin), thalidomide, fetal alcohol exposure, and pregestational diabetes have been associated with microphthalmia/anophthalmia/coloboma complexes in epidemiologic studies.
• Syndromic associations: CHARGE syndrome, renal coloboma syndrome (PAX2), Cat eye syndrome, Wolf–Hirschhorn, Trisomy 13, among others [2–5].

Pathophysiology

The anatomic defect follows the path of the embryonic fissure (typically inferonasal). Posteriorly, absence of RPE and choroid exposes sclera; the intercalary membrane (dysplastic retina) overlies the defect and is prone to breaks at the junctional zone (“locus minoris resistentiae”), predisposing to retinal detachment. Optic nerve coloboma reflects incomplete closure of the proximal fissure with excavation and dysplasia of the disc and peripapillary retina. Iris coloboma represents a full-thickness defect of iris tissue, producing a keyhole pupil and glare. Eyelid coloboma creates an eyelid margin defect, risking corneal desiccation and exposure keratopathy.

Epidemiology

• Prevalence: Ocular coloboma is estimated at approximately 1 in 10,000 live births; rates vary by ascertainment and inclusion criteria [6].
• Laterality: Unilateral or bilateral; bilateral involvement is more often associated with posterior defects and systemic syndromes [1,2].
• Sex/ethnicity: No consistent sex predilection; ethnic variation reported but inconsistent.
• Co-occurrence: Frequently coexists with microphthalmia; the combined microphthalmia–anophthalmia–coloboma (MAC) spectrum has a higher prevalence than isolated coloboma [1,6].

Classification

• By location:
  • Eyelid coloboma (upper > lower lid)
  • Iris coloboma
  • Lens coloboma (zonular/capsular notch)
  • Ciliary body coloboma
  • Chorioretinal coloboma
  • Optic nerve coloboma
• By extent: Focal vs extensive; macula-involving vs sparing; unilateral vs bilateral.
• By pattern: Typical (inferonasal, along fissure) vs atypical (superior/temporal; rare).
• By association: Isolated ocular vs syndromic (e.g., CHARGE).
• Related anomalies: Morning glory disc anomaly and optic disc pit (distinct but overlapping spectrum of optic nerve malformations).

Symptoms and Signs

• Iris coloboma

  • Symptoms: Photophobia, glare, monocular diplopia, cosmetic concern.
  • Signs: Keyhole or oval pupil directed inferonasally; transillumination; may have associated lens/ciliary anomalies.

• Chorioretinal coloboma

  • Symptoms: Reduced central vision if macula involved, scotomas/visual field defects, decreased night vision; may be asymptomatic if extramacular and small.
  • Signs: Well-demarcated white scleral excavation with absent RPE/choroid; intercalary membrane; border often pigmented; frequent association with microphthalmia.

• Optic nerve coloboma

  • Symptoms: Variable acuity loss, visual field defects; if associated with serous maculopathy, distortion and decreased vision.
  • Signs: Enlarged, excavated disc with irregular margins; peripapillary atrophy; associated anomalies (optic pit, morning glory anomaly).

• Lens/ciliary body coloboma

  • Symptoms: Blurred vision from induced astigmatism; may have anisometropia.
  • Signs: Lens notch with focal zonular absence; phacodonesis; potential cataract.

• Eyelid coloboma

  • Symptoms: Ocular surface irritation, tearing, photophobia.
  • Signs: Full-thickness eyelid margin defect with absent lashes; punctate epithelial erosions or ulceration from exposure if large or central.

• Associated ocular findings

  • Strabismus, nystagmus (especially with bilateral posterior involvement), cataract, glaucoma or angle anomalies, persistent fetal vasculature.

Complications

• Retinal detachment from breaks in the intercalary membrane or at the coloboma edge [1,7].
• Serous maculopathy in optic disc anomalies (less common in classic disc coloboma than in optic pits or morning glory).
• Choroidal neovascularization at the junctional zone.
• Cataract and zonular instability.
• Glaucoma (angle dysgenesis; risk variable).
• Exposure keratopathy and infectious keratitis in eyelid coloboma.
• Amblyopia from deprivation or anisometropia in children.

Diagnosis

Clinical evaluation

• Comprehensive eye examination with cycloplegic refraction.

• Slit-lamp biomicroscopy to assess iris, lens, and anterior segment anomalies; intraocular pressure measurement.

• Dilated fundus examination to define extent, macular involvement, and vitreoretinal interface; careful examination of the coloboma border for retinal breaks.

• Ocular surface evaluation in eyelid coloboma to document exposure.

• Systems review and physical examination for syndromic features (CHARGE: coloboma, heart defects, choanal atresia, growth/developmental delay, genitourinary anomalies, ear anomalies).

Imaging and laboratory testing

• Optical coherence tomography (OCT): delineates macular anatomy, intercalary membrane, peripapillary changes; detects serous detachment.
• B-scan ultrasonography: useful in microphthalmia, media opacity, and to assess posterior extent.
• Widefield fundus photography: documentation and longitudinal comparison.
• Fluorescein angiography: selectively for CNV suspicion or to characterize disc anomalies.
• Visual field testing: quantifies scotomas and field loss in cooperative patients.
• Genetic evaluation: referral for gene panel testing or exome sequencing when bilateral/posterior involvement, positive family history, or syndromic features are present [2–4].
• Systemic studies tailored to suspicion:
  • CHARGE workup: temporal bone CT/MRI, cardiac evaluation, ENT assessment [3].
  • PAX2-related renal coloboma: renal ultrasound, serum creatinine, urinalysis [4].
  • Brain/orbit MRI when midline defects or optic nerve hypoplasia suspected.

Differential diagnosis

Treatment

Medical management

• Optical correction: Full refractive correction (glasses or contact lenses); address anisometropia early to prevent amblyopia.
• Amblyopia therapy (pediatric): Occlusion patching of the dominant eye (e.g., 2–6 hours/day based on age and severity) or atropine 1% penalization on weekends; follow AAO/AAPOS protocols [8].
• Photophobia management (iris coloboma): Tinted spectacles; prosthetic/tinted soft contact lenses for cosmesis and glare reduction.
• Ocular surface protection (eyelid coloboma, exposure): Frequent preservative-free lubricating drops/ointments; moisture chamber; eyelid taping at night until surgical repair; manage exposure keratitis per standard care.
• Intraocular pressure control: Topical glaucoma agents if glaucoma is present; agent choice individualized (e.g., beta-blockers, carbonic anhydrase inhibitors). Pediatric prostaglandin analogs have variable efficacy; specialist management recommended.
• Low vision rehabilitation: Orientation and mobility training, assistive devices, school accommodations, and state services for visually impaired children and adults.

Note: There is no pharmacologic therapy that “closes” a coloboma.

Procedural and surgical management

• Iris repair (pupilloplasty/iridoplasty): For symptomatic photophobia or cosmesis; techniques include cerclage or sectoral suturing to round the pupil. Representative CPT: 66680 (repair of iris).
• Eyelid coloboma repair: Timing depends on defect size/location; large or central defects threatening the cornea are repaired in the neonatal period. Techniques include direct closure, semicircular or Tenzel flap, or grafts as needed. CPT examples: 67961–67966 (full-thickness eyelid defect repair, by extent).
• Cataract/lens surgery: Consider when visually significant; anticipate zonular weakness and consider capsular tension devices; increased retinal detachment risk warrants careful counseling and follow-up.
• Prophylactic laser photocoagulation: Barrage laser around the chorioretinal coloboma border is performed by many to reduce retinal detachment risk, particularly when the junction involves or approaches the macula; supportive evidence is retrospective and nonrandomized [7, VERIFY].
• Retinal detachment repair: Pars plana vitrectomy (often with perfluorocarbon liquids, endolaser at the coloboma edge, and silicone oil tamponade) with or without scleral buckle; outcomes depend on macular involvement and extent of coloboma. Representative CPT: 67036 (PPV), 67108 (RD repair with buckle), 67113 (complex RD repair).
• Management of serous maculopathy in optic disc anomalies: Options include PPV with/without internal limiting membrane peel and peripapillary laser; evidence is limited to case series.

Special populations

• Pediatric: Early cycloplegic refraction, prompt amblyopia therapy, and vigilant monitoring for strabismus, nystagmus, and retinal complications. Coordinate care for developmental and systemic issues in syndromic cases (e.g., CHARGE).
• Pregnancy/lactation: No specific coloboma-directed medication issues. Preconception counseling focuses on avoidance of teratogens (e.g., isotretinoin) and optimization of diabetes control; genetic counseling if familial disease is suspected.
• Immunocompromised: No condition-specific modifications for isolated coloboma; manage ocular surface infections aggressively if exposure is present.
• Older adults: Standard management; consider cumulative retinal detachment risk and comorbid ocular disease (e.g., cataract, glaucoma).

Prognosis

Visual outcomes range from normal (isolated iris coloboma) to severe impairment (extensive posterior involvement, macular/optic nerve defects, recurrent retinal detachment). Many patients achieve functional vision with optical correction, amblyopia therapy, and low vision rehabilitation. Long-term surveillance is indicated because retinal detachment and other complications can occur decades after diagnosis [1,7].

Prevention and Patient Counseling

• Genetic counseling to discuss recurrence risk, testing options, and reproductive planning; offer to families with bilateral/posterior or syndromic disease.
• Maternal health and teratogen avoidance: Optimize pregestational diabetes control; avoid retinoic acid derivatives and alcohol in pregnancy.
• Sunlight and glare protection, especially with iris defects.
• Educate on warning symptoms of retinal detachment and establish urgent access to ophthalmic care.
• For eyelid coloboma, stress corneal protection until surgical repair to prevent exposure keratitis and vision loss.

When to Seek Immediate Care

• New flashes of light, a sudden shower of floaters, or a dark curtain/shadow in vision (possible retinal detachment).
• Sudden, significant vision loss in either eye.
• Eye pain, redness, or light sensitivity with decreased vision (possible keratitis or glaucoma).
• In infants with eyelid coloboma: inability to close the eye, corneal drying, or a visible corneal ulcer.
• Any eye injury.

References

1. Gregory-Evans CY, Williams MJ, Halford S, Gregory-Evans K. Ocular coloboma: A comprehensive review. Surv Ophthalmol. 2004;49(5):451-470. doi:10.1016/j.survophthal.2004.06.009
2. Patel A, Sowden JC. Genes and pathways in optic fissure closure and ocular coloboma. Front Genet. 2019;10:868. doi:10.3389/fgene.2019.00868.
3. Bergman JEH, Janssen N, Hoefsloot LH, Jongmans MCJ, Hofstra RMW, van Ravenswaaij-Arts CMA. CHARGE syndrome: the phenotypic spectrum of mutations in the CHD7 gene. J Med Genet. 2011;48(5):334-342. doi:10.1136/jmg.2010.087106.
4. Bower M, Salomon R, Allanson J, et al. Update of PAX2-related disorders: Renal coloboma syndrome. GeneReviews. 2022. https://www.ncbi.nlm.nih.gov/books/NBK1451/
5. AAPOS. Coloboma. American Association for Pediatric Ophthalmology and Strabismus. 2024. https://aapos.org/glossary/coloboma
6. National Eye Institute. Facts About Microphthalmia, Anophthalmia, and Coloboma. 2023. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/microphthalmia-anophthalmia-and-coloboma
7. Uhumwangho OM, Jalali S. Chorioretinal coloboma in a paediatric population: Observations from a tertiary eye care centre in South India. Eye (Lond). 2014;28(6):728-732. doi:10.1038/eye.2014.75. [Includes data on RD risk; geography non-US]
8. American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Panel. Amblyopia Preferred Practice Pattern. 2022. https://www.aao.org/preferred-practice-pattern/amblyopia-ppp-2022

[Additional current references may be added in editorial review to replace older or non-US data.]

ICD-10-CM

• Q13.0 Coloboma of iris
• Q14.1 Coloboma of choroid
• Q14.2 Congenital malformation of optic disc (includes optic disc coloboma)
• Q10.3 Other congenital malformations of eyelid (includes eyelid coloboma)

Disclaimer: This article is for informational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified eye care professional about your specific condition. If you have sudden vision loss, severe eye pain, or an eye injury, seek emergency care immediately.