From The MS Information Sourcebook, produced by the National MS Society.
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 55% of people with MS will have at least one episode of optic neuritis. Frequently, it is the first symptom of MS.
Acute Blurring or Loss of Vision, Usually in One Eye
Optic neuritis is generally experienced as an acute blurring, graying, 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. Loss of vision usually reaches its maximum extent within a few days, and generally improves within 4 to 12 weeks without treatment.
Recent studies suggest that a short course of methylprednisolone administered intravenously, sometimes followed by a tapered course of oral steroids may be useful in helping to reverse the inflammation and restore vision more quickly. There is, however, no definitive evidence that treatment with steroids produces a more complete recovery than that which would have happened 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.
Clinical Bulletin for Healthcare Professionals
Kalb R. (ed.) Multiple Sclerosis: The Questions You Have; The Answers You Need (3rd ed.). New York: Demos Medical Publishing, 2004.
—Ch. 2 Neurology
—Ch. 3 Treatment
Schapiro R. Managing the Symptoms of Multiple Sclerosis (5th ed.). New York: Demos Medical Publishing, 2007.
—Ch. 14 Vision
—Ch. 15 Pain