Optic neuritis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Mohamadmostafa Jahansouz M.D.[2]

Historical Perspective

Discovery

• Optic neuritis was first discovered by von Graefe and Nettleship, in late nineteenth century when ophthalmoscopy became part of the ophthalmic examination.
• The association between systemic sclerosis and optic neuritis was made by the early 1900's but there was much controversy and misunderstanding about its differential diagnosis, pathogenesis, and possible treatment.
• Optic neuritis was first distinguished from infectious,hereditary, toxic, nutritional, and ischemic optic neuropathies during the twentieth century.
• During late twentieth century, the development of MRI and the results from recent clinical trials, discovered the relationship between optic neuritis and multiple sclerosis.

Classification

Optic neuritis may be classified into atypical or typical subtypes based on its clinical features.

• Atypical optic neuritis entails clinical manifestations that deviate from classic pattern of optic neuritis features.
• Atypical features to consider include:
  • Lack of pain
  • Simultaneous or near-simultaneous onset
  • Lack of response to or relapse upon tapering from corticosteroids
  • Optic neuritis due nerve head or peripapillary hemorrhages

Pathophysiology

Pathogenesis

• The exact pathogenesis of optic neuritis is not completely understood.

• But It is likely due to some inflammatory process which leads to delayed type IV hypersensitivity reaction induced by released cytokines and other inflammatory mediators from activated peripheral T-cells which can cross the blood brain barrier and cause destruction of myelin, neural cell death and axonal degeneration.
• In addition to involvement of the myelin sheath (white matter), latest technologies such as optical coherence tomography (OCT) suggest involvement of axons (gray matter) in this process.

• Findings suggestive of optic neuritis in microscopic histopathological analysis include:
  • Reduced axon counts
  • Optic atrophy
  • Inflammation
  • Demyelination
  • Axonal loss
  • Intracellular neurofilaments

Causes

• The exact cause of optic neuritis is unknown.
• But It is likely due invasion of the immune system to the myelin, resulting in inflammation and damage to the myelin.

The following autoimmune are associated with optic neuritis:

• Multiple sclerosis:
  • Multiple sclerosis is the first main cause of optic neuritis.
  • 50% of patients with multiple sclerosis finally develop optic neuritis.
• Neuromyelitis optica
  • In Neuromyelitis optica, inflammation recurs in the optic nerve and spinal cord.

• Infections:
  • Lyme disease
  • Cat-scratch disease
  • Syphilis
  • Measles
  • Mumps
  • Herpes simplex

Differentiating Optic Neuritis from other Diseases

Optic neuritis must be differentiated from other diseases that cause sudden eye pain and vision loss such as:

1. Leber’s Hereditary Optic Neuropathy (LHON) which results from point mutations in mitochondrial DNA and subsequent mitochondrial dysfunction, causing bilateral central vision loss.
2. Nonarteritic Anterior Ischemic Optic Neuropathy (AION)
   • It is the most common form of ischemic optic neuropathy and the second most common optic neuropathy.
   • It is more common in patients over the age of 50 years with vasculopathic risk factors such as:
     • Diabetes mellitus
     • Hypertension
     • Obstructive sleep apnea

Epidemiology and Demographics

Incidence

• The incidence of optic neuritis is approximately 5 to 6.4 per 100 000 individuals in US.

Age

• Optic neuritis commonly affects patients between the ages of 15 and 49.

Race

• Optic neuritis usually affects individuals of the Caucasians race eight times more frequently than Blacks and Asians.
• Black populations individuals are less likely to develop optic neuritis.

Gender

• Women are more commonly affected by optic neuritis than men.

Region

• The incidence of optic neuritis is highest in populations located at higher latitudes such as:
  • Northern United States
  • Northern and Western Europe
  • New Zealand and Southern Australia

Risk Factors

Common Risk Factors

• Common risk factors in the development of optic neuritis include:
  1. Age
     • Optic neuritis most often affects adults between the ages of 15 and 49.
  2. Sex
     • Women are much more likely to develop optic neuritis than men are.
  3. Race
     • Optic neuritis usually affects individuals of the Caucasians race eight times more frequently than Blacks and Asians.
     • Black populations individuals are less likely to develop optic neuritis.
  4. Genetic mutation
  5. Multiple sclerosis
  6. Trauma
  7. Nutritional deficiencies
  8. Compression of the optic nerve
  9. Arteritic optic neuropathy
  10. Diabetes
  11. Glaucoma
• Common risk factors in the recurrence of optic neuritis include:
  1. Underlying diseases such as:
     • Neuromyelitis optica
     • Multiple sclerosis
  2. Unilateral optic neuritis
  3. Early initiation of glucocorticoid

Natural History, Complications and Prognosis

Natural History

• The symptoms of optic neuritis usually develop in the second decade of life, and start with symptoms such as pain on movement of the eyes, followed by a worsening of vision.
• Common symptoms of optic neuritis include:
  1. Pain on movement of the eyes which is sever and so disturbing
  2. Seeing things darkly, unclearly, and with poor contrast
  3. Dirty and pale Colors
  4. Visual field loss
  5. Disturbed color vision
  6. Flashing lights
• After a sub acute onset, the patient’s visual acuity continues to deteriorate for a few more days; in the untreated course of the disease, it generally reaches its nadir in one to two weeks and then improves again.

Complications

• Common complications of optic neuritis include:
  • Side effects of corticosteroids use
  • Permanent optic nerve damage
  • Decreased visual acuity
    • In some cases of optic neuritis, partial loss of color discrimination might persist.

Prognosis

• The long-term visual prognosis of idiopathic optic neuritis is generally good.
• More than 90% of the patients recover a visual acuity of 20/40 or better by 6 months.
• Findings associated with poor visual outcome at 6 months include:
  • A cut-off level of vision ≤ 20/50
  • Contrast sensitivity of <1.0 log units
  • A visual field mean deviation of ≤ – 15 dB after 1 month in the Optic Neuritis Treatment Trial.
• Despite the relatively good visual outcome, most patients show a degree of long-lasting damage to the optic nerve, such as:
  • A pale optic disc
  • Loss of retinal nerve fibers
  • Prolonged latency in the visual evoked response
  • Thinning of the optic nerve on MR

Diagnosis

Diagnosis studies

The diagnosis of typical optic neuritis is usually made clinically.

The classic triad for diagnosis of optic neuritis consist of:

1. Visual loss
2. Periocular pain
3. Dyschromatopsia

MRI is the diagnosis study of choice for visualising the optic nerve.

The following result of MRI is confirmatory of optic neuritis:

• Swollen retrobulbar intra-orbital segment of the optic nerve with a high T2 signal. High T2 signal persists and may be permanent;
• Atrophied nerve in chronic cases

Other diagnosis studies which may help to diagnosis of optic neuritis include:

• Functional MRI
• Multifocal visual evoked potential
• Optical coherence tomography (OCT)

Symptoms

• The symptoms of optic neuritis usually develop in the second decade of life, and start with symptoms such as pain on movement of the eyes, followed by a worsening of vision.
• Common symptoms of optic neuritis include:
  1. Pain on movement of the eyes which is sever and so disturbing
  2. Seeing things darkly, unclearly, and with poor contrast
  3. Dirty and pale Colors
  4. Visual field loss
  5. Disturbed color vision
  6. Flashing lights
• After a sub acute onset, the patient’s visual acuity continues to deteriorate for a few more days; in the untreated course of the disease, it generally reaches its nadir in one to two weeks and then improves again.

Physical Examination

Physical examination of patients with optic neuritis is usually remarkable for:

• Ophthalmic examination findings:
  • Papillitis with swollen optic disc
  • Normal optic disc appearance (2/3 of cases) in retrobulbar neuritis type of optic neuritis
  • Perineuritis, which involves the optic nerve sheath while the optic disc may or may not be swollen
  • Neuroretinitis with optic disc oedema and macular star exudates
• Unilateral loss of visual acuity
• Reduced contrast sensitivity
• Ipsilateral relative afferent pupillary defect
• Visual field defect
• Dyschromatopsia

References

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