Definition of optic neuritis
Inflammation involving the optic nerve, the bundle of nerves that transmits visual information from the eye to the brain, with pain and temporary loss of vision being common symptoms.
Optic neuritis is often associated with multiple sclerosis, which often leads to inflammation and damage to nerves in the brain and spinal cord. Some of the first symptoms of multiple sclerosis are optic neuritis.
In Asian populations, there is perhaps a closer association with optic neuromyelitis optica (note: not confirmed by observational studies).
Vision is eventually restored in most people with a single episode. Steroid hormone therapy can accelerate recovery of vision.
Optic neuritis symptoms
Optic neuritis usually involves a single eye and symptoms include
Eye pain: Most patients have eye pain that worsens when the eye is turned, sometimes as a dull pain behind the eye.
Vision loss: Most present with temporary, varying degrees of vision loss, usually occurring over a period of hours to days, which can be worsened by exercise or hot baths, and some patients may experience permanent vision loss.
Color vision abnormalities: Color perception is often impaired and is not vibrant enough compared to normal colors.
Light flicker: Some patients complain of flashes of light in front of their eyes.
Etiology
The exact cause remains unclear, but it is generally believed that the immune system mistakenly targets a substance (myelin) that encases the optic nerve, leading to myelin inflammation and damage.
Normally, myelin helps electrical impulses travel quickly from the eye to the brain to form visual information in the cerebral cortex; inflammation disrupts this process leading to vision loss.
Disease states often associated with autoimmunity.
Multiple sclerosis: often involving the brain and spinal cord, patients with optic neuritis have about a 50% chance of developing multiple sclerosis, and those with focal brain MRI after optic neuritis are at higher risk.
Optic neuromyelitis optica: Inflammation primarily invades the optic nerve and spinal cord and has similarities to multiple sclerosis, but with fewer intracerebral lesions. Optic neuritis optica associated with optic neuritis optica generally presents more severely than optic neuritis optica associated with multiple sclerosis.
There are other autoimmune related conditions, such as systemic lupus erythematosus and nodular disease, that can also present with optic neuritis episodes.
Other factors that may be associated with episodes of optic neuritis include
Infections: bacteria such as syphilis, Lyme disease, and cat-scratch fever, and viruses such as measles, mumps, and herpes
Medications: such as ethambutol for the treatment of tuberculosis.
Risk factors
Risk factors for optic neuritis due to autoimmune diseases include
Age: Optic neuritis most often affects young adults aged 20 to 40 years.
Gender: Women are more likely to develop optic neuritis than men (ratio 3:1).
Race: Optic neuritis occurs more often in whites than in blacks.
Genetic mutations: Certain genetic mutations may increase the risk of developing optic neuritis.
Complications
Optic nerve damage: Most people have optic nerve damage, and to a lesser extent, they may not have any symptoms.
Vision loss: most return to normal or near normal several months after onset; color vision impairment may persist for a long time in some patients; vision loss may remain unrecovered after inflammation is controlled.
Side effects of treatment: Steroid drugs cause the body to become more susceptible to infection. Long-term steroid hormone use may also lead to osteoporosis and femoral head necrosis.
Examination and diagnosis
Routine examination: including visual acuity and color vision.
Ophthalmoscopic examination: 1/3 of patients have optic disc edema.
Visual evoked potentials: the brain’s response to visual stimuli. Slowed optic nerve conduction can be detected.
Magnetic resonance imaging (MRI) scan: May show inflammatory changes in the optic nerve, and injection of enhancer may show optic nerve and intracerebral lesions more clearly.
MRI to look for the presence of brain lesions can help predict the risk of developing multiple sclerosis; it also rules out other causes of vision loss, such as tumors.
Blood tests: AQP4 antibodies may be checked, especially in patients with severe optic neuritis. Serologic tests associated with systemic diseases can help identify other causes.
Treatment and medications
It can recover on its own, and steroid hormones help to relieve the inflammation of the optic nerve (from European and American studies).
Intravenous steroid hormone therapy is usually used to accelerate vision recovery, but does not appear to affect the ultimate degree of vision recovery (compared to self-recovery). Steroid hormones have also been used to reduce or slow the risk of developing multiple sclerosis.
In severely ill patients for whom steroid hormones are ineffective, plasma replacement therapy may help with vision recovery.
Prevention of multiple sclerosis
Medications such as interferons (interferon beta-1a and interferon beta-1b) may have a preventive effect against multiple sclerosis in patients with lesions in the brain on MRI brain scans.
Prognosis
Most patients recover normal or near-normal vision within 12 months.
Optic neuritis due to multiple sclerosis or optic neuromyelitis optica has a high risk of relapse, as well as relapse of unknown etiology, but the long-term prognosis is relatively good.