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Optic Neuritis
Sudden vision loss is one of the more common problems encountered in ophthalmology and neurology.

Optic neuritis, a demyelinating inflammatory condition that causes acute vision loss, is associated with multiple sclerosis (MS), and recognizing its classic clinical manifestations (signs) early is important so that appropriate diagnostic testing and treatment can be started. The most common etiology (cause) of optic neuritis is MS.

The signs and symptoms of optic neuritis may be indications of an autoimmune such as MS. In 15 to 20% of those who eventually develop MS, optic neuritis is their first symptom. Studies have shown that up to 50% of patients with MS will develop an episode of optic neuritis, and 0.5% of the time optic neuritis is the presenting sign of MS.

Vision Loss and Eye Pain

Vision loss in optic neuritis typically occurs over several hours to days, and vision loss is usually at its worst within 1 to 2 weeks. Typically, patients begin to recover 2 to 4 weeks after the onset of the vision loss. The optic nerve may take up to 6 to 12 months to heal completely, but most patients recover as much vision as they are going to within the first few months.

In some cases there may be a permanent reduction in sight, this is when continued episodes cause scarring on the optic nerve. Studies have shown that more than two-thirds of patients have full 20/20 vision once they have fully recovered. Irreversible optic nerve damage occurs in up to 85% of those with optic neuritis; however, the damage is often early on and mild enough to allow full visual recovery. As many as 80% of patients regain at least 20/30 vision, with 45% within the first 4 months and 35% within 1 year. Long-term severe vision loss occurs in about 20% of patients and about 3% become completely blind.

Studies have also shown that about 87% of thoses with optic neuritis, eye pain is very common and typically worsens with eye movement. The eye itself is usually sore to the touch. The pain generally begins at the same time as the visual loss and improves along with it. Eye movements also may bring about photopsia (flickering or flashes of light) to about 30% of those with optic neuritis.

Loss of color vision out of proportion to the loss of visual acuity is characteristic of optic neuropathies. Studies have shown that nearly 90% of the involved eyes had abnormal color vision. The most common patterns of color vision loss in optic nerve disease are loss of red (protanopia) and green (deutranopia).

Most Common in Young Women

Acute demyelinating optic neuritis most often affects women in their 20s and 30s. Studies have estimated its annual incidence to be about 6 per 100,000. The incidence, just like MS, are higher in populations at higher latitudes and lower near the equator. It's also less common in blacks than in whites.

In children, optic neuritis is not as strongly associated with MS, especially when there is optic disc swelling or bilateral involvement. Most children have a good visual outcome, but about 20% may be visually disabled to some degree.

Optic neuritis highlights include:
Optic neuritis is more common in women in their 20s and 30s, whereas ischemic optic neuropathy, which is more common, primarily affects older people.
The diagnosis of optic neuritis is primarily clinical, but magnetic resonance imaging (MRI) confirms the diagnosis and, more importantly, assesses the risk of MS.
Intravenous methylprednisolone doesn't affect the long-term visual outcome, but it speeds visual recovery and reduces the risk of MS. A surprising fact is oral prednisone seems to increase the risk of recurrent optic neuritis and is not used.
Early treatment with interferon beta reduces the risk of MS is typically used in patients at high risk.

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Major symptoms of optic neuritis are sudden loss of vision (partial or complete), or sudden blurred or "foggy" vision, and pain on movement of the affected eye. Many patients with optic neuritis may lose some of their color vision in the affected eye, with colors appearing subtly washed out compared to the other eye. Many others tend to have "floating" spots in their vision that is more noticeable in brighter lighting conditions.

Another symptom that may appear is called closed-eye visualizations (CEV) where light appears when one's eyes are closed or when one is in a darkened room. The spots of light are a form of phosphene which are brief spots of light brought on by eye movement (movement phosphenes) or sudden noises (sound phosphenes). They can last for a few seconds to always being present. In the case of optic neuritis, they are caused by mechanical aggravation from a damaged or inflamed optic nerve. They are usually more obvious in low light to dark conditions.

Optic neuritis usually affects one eye, although it may occur in both eyes simultaneously and symptoms may include:
Pain - Most people who develop optic neuritis experience eye pain that's worsened by eye movement. Pain associated with optic neuritis usually peaks within one week and then goes away within several days.
Visual loss - The extent of visual loss associated with optic neuritis varies. Some people experience severe difficulty seeing, while others might not notice any changes in their vision. Vision loss, should it occur, usually develops over the course of a day to two weeks and may be worsened by heat or exercise. Vision loss is usually temporary, but it may be permanent in some cases.
Loss of color vision - Optic neuritis often affects the perception of colors. You may notice that the colors of objects, particularly red ones, temporarily appear "washed out" or less vivid than normal.

What's Happening

The presence of demyelinating white matter lesions on brain are found on MRI at the time of presentation of optic neuritis is the strongest predictor for developing clinically definite MS. Almost half of the patients with optic neuritis have white matter lesions consistent with MS. At five years follow-up, the overall risk of developing MS is 30%, with or without MRI lesions. Patients with a normal MRI still develop MS (16%), but at a lower rate compared to those patients with three or more MRI lesions (51%). From the other perspective, however, almost half (44%) of patients with any demyelinating lesions on MRI at presentation will not have developed MS ten years later.

To understanding why MS causes visual problems, it's important to remember that we don’t actually see with our eyes rather with our brains. Around two-thirds of our brain is involved in processing visual sensory input received through the eyes. The optic nerve is the cable that connects the eye to the brain, and it's this connecting structure that is often damaged in MS, giving rise to optic neuritis.

There are several other pathways in the brain that send signals from the brainstem to the muscles of both eyes, allowing our eyes to move in unison. These motor output pathways are also often affected in MS. If these pathways are damaged, then the eye muscles will not be able to move in a coordinated fashion, resulting in double vision, or involuntary movements of one or both eyes, giving rise to another visual syndrome seen in MS called internuclear ophthalmoplegia. Both visual sensory (input) and eye movement (output) abnormalities are common in MS.

Complications arising from optic neuritis may include:
Optic nerve damage - Most people have some permanent optic nerve damage following an episode of optic neuritis, but they may not experience any symptoms.
Decreased visual acuity - Vision loss may persist after optic neuritis has improved. Up to 10% of people with a history of optic neuritis have some degree of long-term vision loss.
Side effects of treatment - Steroid medications used to treat optic neuritis subdue the immune system, which causes your body to become more susceptible to infections. Long-term use of steroids may also cause osteoporosis.
Neuromyelitis Optica (Devic Disease)
Neuromyelitis optica (Devic disease) is a combination of optic neuritis and transverse myelitis. Clinically, the disease spares the nervous system except for the optic nerves and spinal cord. It doesn't cause damage to the nerves in the brain as often as MS does. The onset of the optic neuritis may precede or follow the onset of the transverse myelitis by up to 2 to 4 years. Usually, the optic neuritis is bilateral and retrobulbar and results in severe vision loss, worse than that seen in patients with MS.

The transverse myelitis may cause paraplegia or quadriplegia, depending on the location of the lesion in the spinal cord (cervical vs thoracic). The transverse myelitis in neuromyelitis optica is distinct from that seen in MS. In neuromyelitis optica, the transverse myelitis is longitudinally extensive, spanning more than three vertebral bodies in length. In MS, spinal cord lesions usually are more discrete and involve one or two spinal cord segments.

Recently, serum neuromyelitis optica immunoglobulin G (IgG) antibody has been shown to be a significant biomarker of this disease. Its sensitivity ranges from approximately 60 to 70% and its specificity is greater than 90%. This antibody binds to aquaporin-4, an important water-channel protein in the blood-brain barrier of the central nervous system, and evidence suggests that it's involved in the pathogenesis of the disease.

Initially, it was proposed that MRI of the brain had to be normal for neuromyelitis optica to be diagnosed. However, the proposed 2006 criteria allow for some abnormal T2 and fluid-attenuated inversion recovery (FLAIR) hyperintensities in the periaqueductal gray matter and diencephalon.

It's still debated whether neuromyelitis optica is a separate disease from MS or a subset of it. The implications of this debate may affect its management, as discussed below.

Those who have optic neuritis without a disease such as MS have a good chance of recovery. However, optic neuritis caused by MS or other autoimmune diseases such as systemic lupus erythematosus has a poorer outlook.