BASICS

DESCRIPTION

Myelinated (Medullated) Nerve Fibers

• White striated patches at the upper and lower poles of the optic disc of varying severity

• Frayed and feathered edges follow path of normal retinal fibers

• Retinal vessels that pass through the superficial layers of the nerve fibers are obscured

• Patches or slits of normal appearing retina may occasionally be visible within the area of myelination

• Myelinated fibers are discontinuous with the optic nerve head in approximately 20% of cases

• Can rarely be acquired after infancy and even in adulthood (trauma appears to be common denominator in these cases)

EPIDEMIOLOGY

Occurs in approximately 1% of the general population

RISK FACTORS

Genetics

• Has been reported with an autosomal dominant inheritance pattern in familial cases (uncommon)

• Has been reported with Gorlin syndrome: Multiple basal cell nevi, with possible associated medulloblastoma

• Traboulsi described an autosomal dominant vitreoretinopathy characterized by extensive bilateral myelinization of the retinal nerve fiber layer, congenitally poor vision, severe vitreous degeneration, high myopia, retinal dystrophy with night blindness with reduction of electroretinographic responses and limb deformities.

PATHOPHYSIOLOGY

• Possible mechanisms include:

– Defect in lamina cribrosa

– Fewer axons relative to size of scleral canal, thus allowing room for myelination to proceed into the retina

– Late development of the lamina cribrosa may allow oligodendrocytes to migrate into the eye

ETIOLOGY

• Oligodendrocytes (responsible for myelination within the central nervous system) typically begin at the lateral geniculate nucleus at approximately 5 months gestation and terminate at the lamina cribrosa at approximately 40 weeks gestation

• Clinical appearance occurs when fibers in the retina acquire a myelin sheath

COMMONLY ASSOCIATED CONDITIONS

• Amblyopia with or without high myopia in involved eye

• Oxycephaly with abnormal length of the optic nerve (uncommon)

• Tilted disc syndrome

• Anterior segment dysgenesis

• Possibly neurofibromatosis type2 (debated)

DIAGNOSIS

HISTORY

• Possible history of trauma

• History of lesser vision in one eye with or without strabismus

PHYSICAL EXAM

• Full ocular examination including careful evaluation of the optic discs and evaluation for concomitant potentially treatable amblyopia and high myopia

• Evaluate skin for evidence of Gorlin syndrome (uncommon)

DIAGNOSTIC TESTS & INTERPRETATION

Imaging

• Usually none

• Neuroimaging should be considered in any patient with suspected Gorlin syndrome to rule out associated medulloblastoma

Diagnostic Procedures/Other

OCT may be helpful

DIFFERENTIAL DIAGNOSIS

• Tilted disc syndrome with myelinated nerve fibers

• Cotton wool spots/exudate

TREATMENT

MEDICATION

No medical treatment for the primary disorder

ADDITIONAL TREATMENT

General Measures

Appropriate refractive error correction as soon as appropriate with concomitant amblyopia treatment if indicated

Issues for Referral

• Dermatology, if concerned about Gorlin syndrome (uncommon)

• Genetic counseling if indicated

COMPLEMENTARY & ALTERNATIVE THERAPIES

None proven or indicated

SURGERY/OTHER PROCEDURES

Surgery for strabismus if indicated

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

• Regular follow-ups to monitor for changes in refractive error

• As needed for amblyopia monitoring and treatment

PATIENT EDUCATION

Amblyopia management

PROGNOSIS

• Amblyopia associated with high myopia previously thought to be unamenable to amblyopia treatment. Evidence now indicates that some patients will respond to amblyopia therapy.

• Myelinated nerve fibers reported to disappear as a result of tabetic optic atrophy, pituitary tumor, glaucoma, central retinal artery occlusion, and optic neuritis.

COMPLICATIONS

• Amblyopia

• Strabismus

• Refractive error

ADDITIONAL READING

• Nucci. Paulo in Ophthalmic Genetics 1990;11(2):143–145.

• Brodsky MC, Baker RS, Hamed LM. “Pediatric Neuro-Ophthalmology.” Springer; New York: New York, 1996.

• Pollack S. The morning glory disc anomaly; contractile movement, classification, and embryogenesis. Doc Ophthalmol 1987;65:439–460.

• Brown G, Tasman W. “Congenital Anomalies of the Optic Disc.” New York: New York Grune & Stratton, 1983.

• Traboulsi EI, et al. A new syndrome of myelinated nerve fibers, vitreoretinopathy and skeletal malformations. Arch Ophthalmol 1993;111:1543–1545.

• Miller NR. “Walsh and Hoyt’s Clinical Neuro-ophthalmology Baltimore. Maryland: Williams and Wilkins, 1982.

CODES

ICD9

• 367.1 Myopia

• 379.21 Vitreous degeneration

• 743.57 Specified congenital anomalies of optic disc

CLINICAL PEARLS

• Work to maximize visual potential, especially in bilateral cases.

• Protective eyewear if best corrected visual acuity is subnormal in one eye

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