One of the most distinctive initial presentations of MS is an entity called optic neuritis. As the name implies, optic neuritis is an inflammatory disorder of the optic nerve. The optic nerve carries visual information from the eye to the brain. It is considered part of the central nervous system and because of this, its myelin is supplied by oligodendrocytes. Oligodendrocytes are the cells that create myelin for the brain and spinal cord. As a result, the optic nerve is vulnerable to attack from the nervous system in MS.
Clinically, patients with optic neuritis typically complain of blurry vision, and say they feel as if they are looking through wax paper or a dirty window. I have heard many patients believe that they had a problem with their glasses or contact lenses, and it takes them several days until they figure out that the problem is in fact in their eye. Patients will often complain of pain with eye movement as well. In a small number of patients, the optic neuritis may be in both eyes. The symptoms typically progress over several days, and although visual loss is sometimes quite severe, complete visual loss is uncommon.
Most patients recover to a large degree. However many patients do not recover completely. It is common for patients to have residual color deficits, usually of the color red, and difficulty seeing in low-contrast environments. As a result of this, many patients will say that they have trouble seeing at night, even if their visual acuity as measured on a standard eye chart has recovered to its baseline value. Unfortunately, a small number of patients are left with significant visual impairment in the affected eye.
Other than a pupil that does not constrict properly to light, the examination of the eye is normal in typical cases of acute optic neuritis. It is important that patients with suspected optic neuritis, especially those without an established history of MS, be seen by an opthamologist to ensure that the visual loss is not caused by a structural problem of the retina or the blood supply to the optic nerve.
In optic neuritis, an MRI sometimes shows enhancement of the optic nerve with the administration of contrast dye. In the pictures below, the optic nerve is circled and its colored white indicates active inflammation. In my next post, I will discuss the treatment of optic neuritis and the relationship between optic neuritis and MS.