Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Dominantly Inherited Optic Neuropathy

Key Facts

•Slowly progressive binocular visual loss during first decade

•Binocularly symmetric visual acuity loss

•Dominant inheritance

•Mapped to chromosome 3q

•No treatment

Clinical Findings

•Slowly progressive binocular visual loss during first decade

•Visual loss ranges between 20/20 and 20/200 and is usually symmetric

•Bilateral central or cecocentral scotomas

•Wedge-shaped temporal optic disc pallor

•Some patients have sensorineural hearing loss

Ancillary Testing

•Brain imaging to rule out compressive optic neuropathy unless all findings are classic, including clear family history

•Genetic studies valuable for documentation

Differential Diagnosis

•Compressive optic neuropathy

•Psychogenic visual loss

Treatment

• None

Prognosis

• Visual loss stabilizes by end of first decade but does not recover

Fig. 3.18 Dominantly-inherited optic neuropathy. Both optic discs show wedgeshaped temporal pallor.

Fig. 3.19 Centrocecal scotomas (red ovals) are evident on automated (Humphrey) perimetry.

Neuropathy Optic Inherited Dominantly

Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Leber Hereditary Optic Neuropathy

Key Facts

•Subacute visual loss affecting one eye then, after weeks to months, the fellow eye

•Males aged <40 years most at risk

•Slightly swollen, telangiectatic peripapillary nerve fiber layer in affected eye and sometimes in unaffected fellow eye

•Diagnosis based on finding mutation at mitochondrial DNA position 11778, 3460, 14484, or 14459

•Visual loss is generally irreversible

•No known treatment

Clinical Findings

•Subacute onset of painless visual loss in one eye

•Same event weeks to months later in fellow eye

•Visual acuity of 20/100 to finger counting and central or cecocentral scotomas

•May be no afferent pupil defect even when only one eye has suffered visual loss

•Telangiectatic swelling of peripapillary nerve fiber layer in affected eye and sometimes in unaffected fellow eye (pre-eruptive stage)

Ancillary Testing

•Blood test for mitochondrial DNA at position 11778, 3460, 14484, or 14459 will be positive in nearly all cases

Differential Diagnosis

•Optic neuritis

•Compressive optic neuropathy

•Posterior ischemic optic neuropathy

•Anterior ischemic optic neuropathy

•Paraneoplastic optic neuropathy

•Psychogenic visual loss

Treatment

•Patients often placed on mitochondrial cocktail, which includes coenzyme Q10, vitamin E, and B vitamins but no evidence of benefit

• Patients often advised to stop smoking to avoid free radical generation

•Genetic counseling may involve testing of clinically unaffected family members

Prognosis

•Visual loss usually irreversible

• Partial recovery may occur with DNA mutations at positions 14484 and 3460

Fig. 3.20 Leber hereditary optic neuropathy. Right optic disc is hyperemic and the peripapillary retinal nerve fi ber layer is swollen in acute stage of this condition. The left fundus is in the subacute stage, showing nerve fi ber layer thickening and mild temporal optic disc pallor.

Neuropathy Optic Hereditary Leber

47

Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Compressive Optic Neuropathy and

Chiasmopathy

Key Facts

•Visual loss from compression of optic nerves or chiasm by an intraorbital or intracranial mass

•Common causes:

•sphenoid meningioma

•optic nerve sheath meningioma

•craniopharyngioma

•pituitary adenoma

•optic glioma

•teratoma or germinoma

•anterior visual pathway aneurysm

•Visual loss slowly progressive but may occur suddenly

•Treatment is directed at the compressive lesion

Clinical Findings

•Visual acuity and/or visual field loss (nerve fiber bundle defects for optic nerve damage, hemianopic defects for chiasmal damage)

•Afferent pupil defect is common

•Optic discs may appear normal, swollen, or pale

Ancillary Testing

•High-resolution MRI with contrast should detect the lesion, with two exceptions:

1.optic nerve sheath meningioma (see Optic nerve sheath meningioma) requires fat-suppressed, thin-section, postcontrast orbital sequences

2.aneurysm (see Anterior visual pathway intracranial aneurysm) requires dedicated vascular imaging

Differential Diagnosis

•Optic neuritis

•Radiation optic neuropathy

Treatment

•Cranial surgery, endovascular procedures, radiation, or medication (depending on the lesion and other clinical characteristics)

Prognosis

•Visual recovery depends on:

•degree of pre-existing axonal loss

•ability to decompress visual pathway

•lack of complications