The optic nerve allows you to see by carrying images from your retina to your brain. The optic nerve is like a cable of electrical wires or nerve fibers. Each wire carries a part of the visual information to the brain. If some or all of the nerve fibers become inflammed and do not function properly, vision becomes blurred. With optic neuritis, the optic nerve becomes swollen and the nerve fibers do not work properly.
Vision can range from near normal to very poor depending on the number of inflammed nerve fibers.
Various diseases and conditions may cause optic neuritis. In many cases, however, the cause of optic neuritis is not known. The nerve of one or both eyes may be affected. Some people, especially children, develop optic neuritis following a viral illness such as mumps, measles or a cold. In others, optic neuritis may occur as a sign of a neurologic disease affecting nerves in various parts of the body.