Optic neuritis: definition, symptoms, causes, treatment

By Cristiano Antonino On Jun 3, 2023

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Diseases affecting the eyes can be diverse: among the diseases that can affect vision is optic neuritis

What is optic neuritis

Optic neuritis is an inflammation of the optic nerve that can totally or partially impair vision.

It can be caused by a variety of conditions and is most common among young adults in the 20-50 age group.

In most cases it affects only one eye, and is therefore unilateral, but it may affect both sides.

Symptoms of optic neuritis

This inflammation of the optic nerve has different causes and, therefore, the symptoms can also differ.

The most common, however, is mild or severe loss of vision in one or both eyes, which can worsen even abruptly within a few days.

This is because, depending on the reason that triggered it, neuritis is usually temporary and therefore disappears within a few weeks or months.

In general, symptoms attributable to optic neuritis are

loss of vision, total or partial, unilateral or bilateral, central or in the form of a scotoma
ocular pain, particularly when moving the eyes
visual field defects
colour vision disorders (dyschromatopsia)
blurred vision
perception of bright flashes (phosphenes) or spots in the visual field (myodesopsias, flying flies)

A rise in body temperature – as in the case of sun exposure, fever, exercise, hot weather – can temporarily worsen symptoms due to inhibition of nerve conduction of axons that are partly demyelinated.

Causes of optic nerve inflammation

The main cause of optic neuritis is due to degeneration of the myelin sheath that lines and protects the optic nerve, resulting from inflammation of the optic nerve.

Among the most common causes of optic neuropathy is multiple sclerosis, of which neuritis is often one of the first signs.

Other causes are:

infectious diseases, especially viral encephalitis (most common in children), sinusitis, meningitis, tuberculosis, syphilis, HIV, chickenpox, rubella, measles, mumps, shingles and Lyme disease
systemic lupus erythematosus
Behçet’s disease
sardoidosis
metastasis of a malignant tumour along the optic nerve fibres
exposure to substances such as lead, methanol, quinine and arsenic
certain drugs, such as antibiotics
optic neuromyelitis or Devic’s syndrome, i.e. the presence in the blood of autoantibodies directed against aquaporin 4, a protein that stabilises the myelin sheath

Other rarer causes of optic neuritis are

diabetes
pernicious anaemia
systemic autoimmune diseases
Graves’ ophthalmopathy
bee stings
trauma
temporal arteritis
drug-related vasculitis
nutritional deficiencies
cranial radiotherapy

It can be concluded that any process causing inflammation, ischaemia or compression of the optic nerve can cause neuritis.

Diagnosis of optic neuritis

It is important to undergo an ophthalmic examination in the event of symptoms such as loss (even partial) of vision, especially if accompanied by ocular pain and altered colour perception.

The steps to diagnose optic neuritis are different, some are the responsibility of the ophthalmologist, others of the neurologist.

Visual field test

Through this test, the specialist checks visual acuity and colour perception, which is especially useful in patients with unilateral neuritis, as they often do not notice the alterations in the affected eye as the other is functioning normally.

Ophthalmoscopy

The eye fundus test allows us to observe the back of the eye, i.e. the ocular fundus, and especially the optic disc, which represents the insertion area of the optic nerve on the retina.

If the optic disc is swollen, neuritis is present, but only one third of affected patients have this abnormality.

Visual evoked potential

This neurophysiological investigation evaluates the brain’s reaction to certain visual stimuli by applying electrodes to the patient’s head.

It is a test to detect any reduced electrical conduction of the optic nerve, and is particularly useful in people without major symptoms.

Pupillary reflex to light

The pupillary reflex to light is the pupil’s ability to dilate (mydriasis) or constrict (miosis) depending on light: when the optic nerve is inflamed, the pupil’s reaction is impaired.

Other ophthalmic examinations that are useful for detecting inflammation of the optic nerve are optical coherence tomography and the colour diagnostic test.

Blood tests can also be prescribed to detect any ongoing inflammatory processes or the presence of anti-myelin antibodies or infection.

Finally, an MRI may be important in the diagnosis of optic neuritis, particularly in patients who already have symptoms, in order to detect possible lesions in the central nervous system.

The MRI is also the test that determines whether the myelin is damaged, which is why it is very useful for diagnosing multiple sclerosis, one of the main causes of optic neuritis.

Treatment of optic neuritis

Optic neuritis is often a temporary disorder and, as such, tends to disappear within a short time, which varies depending on the cause of the inflammation.

When the cause is attributable to multiple sclerosis or neuromyelitis optica, corticosteroid drugs are generally used, initially intravenously and then orally.

There are also immunomodulatory or immunodepressant drugs to reduce the future incidence after the first treatment.

If the cause is an infection, it should be treated instead, if bacterial with antibiotics. In the case of a tumour, action should be taken to reduce the pressure.

In other cases, the symptoms subside until they disappear completely with the disappearance of the disorder that caused them.