Optic Neuritis

What is Optic Neuritis?

Optic Neuritis (ON) is an inflammation, accompanied by demyelination, of the optic nerve (Cranial Nerve II), which serves the retina of the eye. It is one of the most common initial symptoms of multiple sclerosis (MS), though other causes exist. In fact, ON is the most common presenting symptom at the onset of MS, affecting only one eye in 70% of cases. Most cases of ON, MS-related or not, are caused by demyelination.

Who is Affected?

Optic neuritis can affect both children and adults, involving one or both optic nerves. It typically impacts young adults aged 18-45, with a mean age of 30-35 years. Women are approximately twice as likely as men to experience ON, and the prevalence is higher in Caucasians than in other racial groups. racial groups. 

Symptoms of Optic Neuritis

The primary symptom is loss of vision, ranging from mild blurring to partial or complete blindness, which can develop over one to two weeks and may worsen with heat and exercise. This vision loss is usually not permanent, though some cases may result in permanent damage. Dyschromatopsia (reduced color vision) occurs in all cases, with reduced color vividness, particularly in reds. If inflammation is not visible on the retina, dyschromatopsia becomes a key diagnostic feature. Almost all individuals with ON experience eye pain, especially with eye movement. The pain peaks within a week and subsides in a few days.

While ON typically affects one eye, both eyes may be involved simultaneously. In cases where only one eye is affected, individuals might not notice subtle visual changes until instructed to close the healthy eye.he healthy eye. 

Diagnosis

A full medical exam, including blood tests, helps rule out other related conditions. The Ishihara color chart and Farnsworth-Munsell hue tests are often used to assess dyschromatopsia. Visual evoked potential tests measure nerve transmission speeds and help diagnose ON. An MRI of the brain is typically performed to check for lesions in the central nervous system, and MRI with gadolinium enhancement may reveal an enlarged optic nerve, which is a common feature in MS diagnosis.s in the brain. 

Causes of Optic Neuritis

ON occurs due to inflammation of the optic nerve, which causes vision loss through swelling and the destruction of the myelin sheath that insulates the nerve. It often results from autoimmune disorders, sometimes triggered by viral infections. In some cases, ON can indicate multiple sclerosis, where the immune system attacks the protective myelin sheath of nerves. Other autoimmune conditions like neuromyelitis optica, which affects the optic nerve and spinal cord, may also cause ON. Infections such as bacterial (Lyme disease, tuberculosis, cat scratch fever) or viral (HIV, hepatitis B, herpes zoster) can also lead to ON. Other conditions include cranial arteritis (inflammation of the skull arteries), diabetes, sarcoidosis, pernicious anemia, and certain drugs. Toxins like lead and alcohol, radiation therapy, and hereditary disorders like Leber’s hereditary optic neuropathy may also cause ON.

Treatment for Optic Neuritis

Treatment focuses on addressing the underlying cause, if identified. If ON is associated with a demyelinating disease like MS, corticosteroids may be used to shorten the disease's duration. Steroids like prednisone and methylprednisolone can accelerate vision recovery, although they do not always affect long-term visual outcomes. IV steroids may reduce the risk of developing MS in the first two years following an ON episode, and they may reduce the frequency of recurrent attacks.

For more extensive visual loss, especially in cases of papillitis without other autoimmune signs, pulsed intravenous methylprednisolone may be prescribed. When MRI scans show MS-related lesions, immunomodulatory or immunosuppressive therapy may be used to prevent future ON episodes.