Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Hypotensive Ischemic Optic Neuropathy

Key Facts

•Acute monocular or binocular visual loss caused by infarction of optic nerve as the result of systemic hypotension • Most patients have arteriosclerotic risk factors • Cardiac bypass or prolonged lumbar spine surgery most common setting • Systemic hypotension often documented in anesthesia record

•Visual loss often not apparent until days after surgery

•Optic disc(s) may be swollen or normal at outset

•If normal, may swell days later

•Affected discs become pale weeks later

•Visual recovery is variable • No effective treatment

Clinical Findings

•Visual loss reported within days of surgery • Visual acuity and/or visual field loss (nerve fiber bundle defects) in affected eye(s) • No afferent pupil defect if both eyes affected equally • Fundi are normal or show swollen optic disc(s)

Ancillary Testing

•Hemoglobin often very low (from blood loss) • Orbit and brain imaging is usually normal

Differential Diagnosis

• Bilateral occipital lobe infarction • Pituitary apoplexy • Optic neuritis

Treatment

•Correct systemic hypotension • Correct anemia • Hyperbaric oxygen is ineffective

Prognosis

• Recovery of vision may occur within weeks but not later

Fig. 3.12 Hypotensive ischemic optic neuropathy. Anesthesia record in a patient undergoing multilevel lumbar spine fusion. Late in the 9-h procedure (red oval), blood pressure has fallen to levels that do not sustain adequate perfusion of the optic nerves.

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OD

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BCross sections

Fig. 3.13 Hypotensive ischemic optic neuropathy. Autopsy specimen in a patient who died of exsanguination.

(A) Sagittal section through the right optic nerve shows that its central core has undergone hemorrhagic infarction. (B) The infarction affected nearly the entire intraorbital segment of both optic nerves. (After Johnson MW et al. Ophthalmology 1987; 94:1577–1584, with permission.)

Neuropathy Optic Ischemic Hypotensive

Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Toxic Optic Neuropathy

Key Facts

•Slowly progressive binocular visual loss from optic neuropathy caused by systemic medications or toxins

•Ethambutol is the most common medication, methanol the most common toxin

•Alcohol may also be an optic nerve toxin but is still listed under nutritional deficiency optic neuropathy (see Nutritional deficiency optic neuropathy)

•Withdrawal of toxic agents is the only effective treatment

•Visual recovery is more likely if offending agent is removed early

Clinical Findings

•Slowly progressive painless binocular visual loss

•Symmetric visual acuity loss in the two eyes rarely worse than 20/200

•Pupil reactions normal

•Optic discs normal or show temporal pallor

•Peripapillary nerve fiber layer edema present in methanol toxicity

•Central or cecocentral scotomas

•Acquired color vision loss

•At-risk patients: those taking >15 mg/kg per day of ethambutol or those who have ingested methanol as a substitute for ethanol

Ancillary Testing

•Blood chemistries show acidosis in acute methanol toxicity

•Methanol toxicity: brain imaging may show high T2 signal in basal ganglia and parieto-occipital white matter

Differential Diagnosis

•Nutritional deficiency optic neuropathy

•Hereditary optic neuropathy (dominant or Leber type)

•Optic neuritis

•Compressive optic neuropathy

•Paraneoplastic optic neuropathy

•Psychogenic visual loss

Treatment

•Discontinue ethambutol

•Treat methanol acidosis

Prognosis

• Visual recovery depends on extent of damage

Fig. 3.14 Ethambutol optic neuropathy. Temporal optic disc pallor is evident in both eyes.

Fig. 3.15 Reversible toxic optic neuropathy caused by linezolid treatment. (A) Ophthalmic fi ndings 11 months after starting linezolid treatment. Top, visual fi elds show central scotomas; middle, optic discs appear normal (patient is pseudophakic in the left eye); bottom, visual evoked potentials show no signal.

(B) Ophthalmic fi ndings 3 months after discontinuing linezolid treatment. Top, visual fi elds have returned to normal; middle, optic discs appear normal; bottom, visual evoked potentials are normal. (After McKinley SH et al. J Neuroophthalmol 2005; 25:18, with

permission.)

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B

Neuropathy Optic Toxic

Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Nutritional Deficiency Optic Neuropathy

Key Facts

•Slowly progressive binocular visual loss from optic neuropathy caused by systemic chronic nutritional deficiency, particularly of B vitamins

•Chronic alcoholism and severe malnourishment are principal settings

•Adequate nutrition and cessation of alcohol intake only effective remedies

•Visual recovery unpredictable

Clinical Findings

•Slowly progressive painless binocular visual loss

•Symmetric visual acuity loss rarely worse than 20/200

•Pupil reactions normal

•Optic discs normal or show temporal pallor

•Central or cecocentral scotomas

•Profound acquired color vision loss

•Peripheral neuropathy common

Ancillary Testing

•Delayed latency visual evoked potentials provide objective evidence of optic neuropathy

•Nerve conduction velocity testing helps diagnose associated peripheral neuropathy

•Blood count to rule out anemia of vitamin B12 deficiency

Differential Diagnosis

•Toxic optic neuropathy

•Hereditary optic neuropathy (dominant or Leber type)

•Optic neuritis

•Compressive optic neuropathy

•Paraneoplastic optic neuropathy

•Psychogenic visual loss

Treatment

•Improve diet

•Stop alcohol intake

•Provide single-dose intramuscular thiamine 100 mg followed by oral thiamine 50 mg/day indefinitely

•Provide intramuscular vitamin B12 if appropriate

Prognosis

• Visual recovery depends on extent of damage

Fig. 3.16 Nutritional deprivation optic neuropathy. Temporal pallor in both optic discs in a patient with a history of chronic heavy alcohol ingestion.

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Fig. 3.17 Nutritional deprivation optic neuropathy: two autopsy specimens from patients who had optic neuropathy in the setting of severe chronic alcoholism. (A) Right optic nerve shows that axon columns (arrow heads) on the temporal side of the nerve head (enclosed by arrows) are narrow compared with the normal nasal side. (B) Cross-section of left optic nerve stained for myelin (black) shows lack of stain in the circular region corresponding to the maculopapillar bundle, which contains small fi bers vulnerable to nutritional deprivation or toxic insult. (A, After Smiddy WE, Green WR. Graefe’s Arch Clin Exp Ophthalmol 1987; 225:321–324; B, after Cogan DG. Neurology of the Visual System. Springfi eld: Charles C. Thomas; 1976: 176.)

Neuropathy Optic Deficiency Nutritional