Optic neuritis is inflammation or demyelination of the optic nerve-- the nerve that transmits light and visual images from the retina to the brain. Because the nerve is located behind (“retro”) the globe of the eye, the condition is also known as retrobulbar neuritis.
It has been estimated that about 66% of people with MS will have at least one episode of optic neuritis. Frequently, it is the first symptom of MS.
Optic Neuritis Causes Acute Blurring or Loss of Vision, Usually in One Eye at a Time
Optic neuritis is generally experienced as an acute blurring, graying (change in color saturation), or loss of vision, most often in only one eye. It is rare that both eyes are affected at the same time. There may or may not be pain in the affected eye. The pain, when it occurs, can be of several types—dull and aching, pressure-like, or sharp and piercing. Loss of vision usually reaches its maximum extent within a few days, and generally improves within 4 to 12 weeks without treatment.
It is Possible to Have Optic Neuritis without Affecting Vision
A person may have a subclinical episode of optic neuritis. That is, there may be inflammation and/or demyelination of the optic nerve that occurs without affecting visual function so that the person is not aware of any changes. In these subclinical cases, visual evoked potential (VEP) testing is still able to demonstrate evidence of lesions or damaged areas along the optic pathways. It is for this reason that VEPs are often used as part of the diagnostic workup; a positive finding can provide evidence of a second demyelinating event even in the absence of visual symptoms.
Not Everyone Who Experiences Optic Neuritis Develops MS
Not everyone who has an episode of optic neuritis goes on to develop MS. Long-term follow-up from the Optic Neuritis Treatment Trial, which involved 388 people with a single episode of optic neuritis, yielded the following:
- The ten-year risk of developing clinically definite MS following a single episode of optic neuritis was 38% for the entire study group; the twelve-year risk was 40%. Most of those who developed MS did so within the first five years after the initial episode of optic neuritis.
- The strongest predictor of MS in the study group was the presence of brain lesions on MRI at the time of the episode of optic neuritis. Within the study group, patients with at least one brain lesion on MRI at the time of the optic neuritis episode had a 56% risk of developing MS within 10 years, while those with no brain lesions had only a 22% risk of developing MS within 10 years.
While other disease processes can cause optic neuritis, MS is the most likely cause in a young, otherwise healthy individual.
Optic Neuritis is Often Treated with Corticosteroids
Studies have suggested that a short course of methylprednisolone administered intravenously, sometimes followed by a tapered course of oral steroids, may help reverse the inflammation and restore vision more quickly. However, if the symptoms of optic neuritis are mild and an MRI does not show any lesions, the doctor may decide to allow the disorder to resolve on its own. Intravenous steroids are used because people treated with oral steroids in the Optic Neuritis Treatment Trial appeared to have an increased risk of recurrence and did not do as well as those who received no treatment.
There is no definitive evidence that treatment with steroids produces a more complete recovery than that which would have happened without treatment.
Eyeglasses Don’t Help Vision Affected by Optic Neuritis
Because the visual changes that occur with optic neuritis are the result of inflammation or demyelination of the optic nerve rather than changes in the shape of the eye, prescription glasses cannot correct the problems.