Optic neuritis is inflammation of the optic nerve. It is a common cause of sudden vision loss in young patients. Inflammation is usually due to autoimmunity.
What is the optic nerve?
The optic nerve is like a fibre-optic cable that carries visual information from the eye to the brain. When light strikes the light-sensitive retina on the back of the eye, the light signals are changed to electrical impulses. These electrical impulses travel along the optic nerve to the brain, where they are processed to create an image.
Diagram showing the optic disc where the optic nerve leaves the eye. The optic nerve transmits visual signals to the brain.
What is inflammation?
Inflammation is a response of the body’s immune system to a stimulus. Usually, these stimulus is infection, injury or irritation. Inflammation is important to fight off infection and help in the healing process. However, it can sometimes be harmful, such as in autoimmunity.
What is autoimmunity?
Humans would not live long if their immune system was not working properly. Constantly, our immune system is fighting off bacteria and viruses.
Sometimes, our immune system can incorrectly identify normal self tissue as foreign. When this occurs, the immune system mounts an immune response against the self tissue. This can cause inflammation and damage to the tissue.
What causes optic neuritis?
Optic neuritis is inflammation of the optic nerve. This inflammation is a result of autoimmunity against the optic nerve. Specifically, the immune system mounts a response against the myelin of the optic nerve. Myelin is a covering of the nerve that is important in the functioning of the nerve.
Just what triggers this immune response is not fully understood. Some known causes include:
• Multiple sclerosis • Previous viral infection • Other diseases (eg autoimmune diseases) • Certain drugs (eg chloramphenicol)
What are the symptoms of optic neuritis?
Optic neuritis usually causes the following symptoms:
• Sudden vision loss • Loss of colour vision • Blurred vision • Eye pain (typically with movement)
How is optic neuritis diagnosed?
Optic neuritis is frequently a clinical diagnosis, meaning that it is diagnosed based on the patient’s symptoms. Sometimes, the doctor can diagnose optic neuritis by looking into the back of the eye with an ophthalmoscope. The optic nerve can be imaged with MRI technology, but this is infrequently done.
Diagram showing the appearance of the optic disc in a patient with optic neuritis. Note how the disc with the nerve head and blood vessels appear swollen.
How is optic neuritis treated?
In most cases, the symptoms of optic neuritis improve over a matter of weeks and do not require treatment (vision may not be restored to its previous level).
If the cause of the optic neuritis is known (for example from a drug), it should be treated as well. The use of oral or intravenous steroids to decrease the inflammation is controversial; at our department we use steroids only for severe cases.
Who treats optic neuritis?
Although all ophthalmologists are trained to treat optic neuritis, a neuro-ophthalmologist will frequently be involved in the care of someone with optic neuritis. A neuro-ophthalmologist is an ophthalmologist who has completed a residency in ophthalmology plus extra training in neuro-ophthalmology.
What is multiple sclerosis?
Multiple sclerosis is a chronic disease (meaning that it lasts for a long time) that causes damage and inflammation of nerves. This results in demyelination of nerves, meaning that the myelin sheath (which is important in the functioning of the nerve) is lost. There is a strong association between multiple sclerosis and optic neuritis.
What is the link between multiple sclerosis and optic neuritis?
In many cases, optic neuritis is a symptom of multiple sclerosis; in fact it is one of the most common first signs of multiple sclerosis and approximately half of patients with multiple sclerosis will at some point have an episode of optic neuritis. In addition, about half of patients with optic neuritis have some signs of multiple sclerosis.
However, just because someone has optic neuritis does not mean that they have (or will get) multiple sclerosis (and vice versa).
