Assumpta Madu

BASICS

DESCRIPTION

• A developmental abnormality caused by failure of complete closure of the embryonic fissure during the fifth week of gestation

• A hole in one of the structures of the eye, such as the eyelid, iris, retina, choroid, or optic nerve

• Coloboma derived from Greek, meaning “curtailed” or “mutilated”

EPIDEMIOLOGY

Incidence

• 0.5–0.7 per 10,000 births

• May be unilateral or bilateral with approximately equal frequency

RISK FACTORS

Genetics

• Most cases are sporadic, some are autosomal dominant or recessive

• Mutation in the PAX2 gene on chromosome 10 has been noted in 50% of cases.

– PAX2 gene expressed in primitive cells of the kidney, ureter, eye, ear, and CNS

GENERAL PREVENTION

Genetic Counseling

PATHOPHYSIOLOGY

Incomplete or abnormal coaptation of the proximal end of the embryonic fissure.

ETIOLOGY

• The iris, retina, and choroid are absent in areas affected

• Usually located inferiorly, because the embryonic fissure is located inferonasally in the developing eye.

COMMONLY ASSOCIATED CONDITIONS

• Eyelid coloboma

– Goldenhar syndrome (upper lid)

– Developmental malformation of the first and second branchial arches associated with epibulbar dermoids, auricular appendages, malformations of the auricle, and hemifacial microsomia

– Treacher Collins syndrome (lower lid)

Downward slanting eyes, micrognathia (small lower jaw), conductive hearing loss, underdeveloped zygoma, drooping part of the lateral lower eyelids, and malformed or absent ears

• Iris/optic nerve coloboma:

– Basal encephalocele

– Results from failure of the surface ectoderm to separate from the neuroectoderm causing a defect in the skull floor with herniation of brain tissue along the cribriform plate or the sphenoid bone

– Renal coloboma syndrome

– Autosomal dominant syndrome characterized by hypodysplastic kidneys and optic nerve abnormalities

– Trisomy 13

– Patau syndrome: Heart and kidney defects

– Sturge Weber

– Phakomatosis associated with port-wine stain of the face, glaucoma, seizures, mental retardation

– Wolf-Hirschhorn syndrome

– Mental retardation, microcephaly, seizures, cleft lip/palate

– Klinefelter syndrome

XXY, most common sex chromosome disorder, small testicles and reduced fertility

• Chorioretinal coloboma ± iris or optic nerve coloboma

– CHARGE syndrome

– Colobomas, Heart defects, choanal Atresia, Retardation of Growth and Ear abnormalities

– Joubert syndrome

– Agenesis of the cerebellar vermis leading to ataxia, hyperpnea, and hypotonia

– Lenz microphthalmia

– Microphthalmia, cataract, nystagmus, and glaucoma

– Walker-Warburg syndrome

– Congenital muscular dystrophy, brain and eye abnormalities

– Focal dermal hypoplasia

– Skin, skeletal system, eye and face abnormalities

– Aicardi syndrome

– Absence of corpus callosum, infantile spasms, distinctive chorioretinal lacunae

– Linear sebaceous nevus syndrome

– Eye, nervous system, and skin abnormalities

– Noonan syndrome

Dwarfism, congenital heart defect, impaired blood clotting

DIAGNOSIS

HISTORY

• Patients are usually asymptomatic unless the optic nerve or macula are involved or if there are secondary effects:

– Patients with eyelid colobomas may complain of dry eye due to exposure

– Patients with iris colobomas may have photophobia

– Blurry vision due to refractive error

– Visual field defects

PHYSICAL EXAM

• Ophthalmoscopy usually suffices to make the diagnosis

• Iris coloboma

– Typical inferonasal keyhole-shaped defect

– Lens may be flattened at the pole corresponding to the coloboma owing to the missing zonule

• Optic nerve coloboma

– Microphthalmia

– Inferiorly decentered, white-colored excavation, with minimal peripapillary pigmentary changes

– Nystagmus if significant visual deprivation

– Leukocoria

– Astigmatism or myopia

– Serous retinal detachment

• Chorioretinal coloboma

– A white area (sclera) is visible in the inferior fundus to a variable extent depending on the size of the defect

– Margins well defined

– Rhegmatogenous retinal detachment

– Often a pigmented border marking the transition from the coloboma to the normal retina or choroid

DIAGNOSTIC TESTS & INTERPRETATION

Imaging

• Eyelid coloboma

– CT scan of the orbits and skull is indicated in patients with Treacher Collins syndrome to document and assess craniofacial structures

• Optic nerve coloboma

– Axial CT scan shows a crater-like excavation of the posterior globe at its junction with the optic nerve

– Coronal T1-weighted MRI confirms the intracranial portion of the optic nerve is reduced in size

– CT and MRI delineates the anatomy of the skeletal defect and the associated cerebral abnormalities in basal encephaloceles

Diagnostic Procedures/Other

• Slit-lamp examination

• Chromosome analysis, especially if other organ system involvement

• B-scan ultrasound to evaluate for posterior cyst

• Renal ultrasound in syndromes with kidney involvement (CHARGE, renal coloboma, Patau)

Pathological Findings

• Optic nerve coloboma

– Intrascleral smooth muscle strands oriented concentrically around the distal optic nerve

– Heterotopic adipose tissue also present within and adjacent to some optic disc colobomas

DIFFERENTIAL DIAGNOSIS

• Iris coloboma

– Ectopia lentis et pupillae

– Iridocorneal endothelium syndrome (ICE)

– Traumatic iris tear

– Aniridia

• Optic nerve coloboma

– Morning glory disc

– Glaucomatous cupping

– Optic nerve pit or staphyloma

– Anterior segment dysgenesis

– Retinopathy of prematurity (ROP)

– Coats disease

– Retinoblastoma

• Chorioretinal coloboma

– Chorioretinal scar (e.g., ocular toxoplasmosis)

– Degenerative myopia

– Trauma

TREATMENT

ADDITIONAL TREATMENT

General Measures

• There are no medical or surgical treatments for colobomas

• Iris coloboma

– Cosmetic contact lenses and sunglasses

– Fully correct refractive error in both eyes with glasses if lenticular astigmatism

• Optic nerve coloboma

– Scleral shell or orbital expander if microphthalmic

– Amblyopia may be treated with patching

• Chorioretinal coloboma

– No treatment is necessary unless retinal detachment or choroidal neovascularization occurs

SURGERY/OTHER PROCEDURES

• Correct strabismus if present

• Monitor and treat for retinal detachment

• Internal drainage through the hole in the intercalary membrane (extracolobomatous inner retinal layers that are extended centrally over coloboma) is performed and laser photocoagulation is placed around the margins of the coloboma.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

• Ophthalmologist

• Pediatrician/Internist

PATIENT EDUCATION

• http://www.rnib.org.uk/eyehealth/eyeconditions/conditionsac/Pages/coloboma.aspx

PROGNOSIS

• Mild or severe depending on the extent and location of the gap or cleft

• Excellent visual prognosis if isolated iris coloboma

• In optic nerve colobomas, visual acuity may be mildly to severely decreased, and is difficult to predict from the appearance of the disc.

COMPLICATIONS

• Amblyopia

• Refractive error

• Glaucoma

• Retinal detachment

• Choroidal neovascularization

ADDITIONAL READING

• Steahly LP. Retinochoroidal coloboma: varieties of clinical presentations. Ann Ophthalmol 1990;22(1):9–14.

• Berk AT, Yaman A, Saatci AO. Ocular and systemic findings associated with optic disc colobomas. J Pediatr Ophthalmol Strabismus. 2003;40(5):272–278.

• McMain K, Blake K, Smith I, et al. Ocular features of CHARGE syndrome. J AAPOS. 2008;12(5):460–465.

CODES

ICD9

• 377.23 Coloboma of optic disc

• 743.46 Other specified congenital anomalies of iris and ciliary body

• 743.62 Congenital deformities of eyelids

CLINICAL PEARLS

• Colobomas arise from a defect in the closure of the embryonic fissure during the fifth week of gestation.

• Visual potential depends on the extent of the retinal, optic nerve, and other organ systems involved.

• Association between coloboma, heart defects, choanal atresia, mental retardation, and genitourinary or ear anomalies (CHARGE).

• There are no medical or surgical treatments for colobomas

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