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.