MULTIPLE SCLEROSIS: VISUAL SYMPTOMS
Visual symptoms are not uncommon in people with Multiple Sclerosis (MS), but rarely result in total blindness. They can result from damage to the optic nerve or from an in coordination in the eye muscles.
Optic Neuritis
Optic Neuritis is one of the most common symptoms of MS, frequently occurring at the onset of MS, and presents unilaterally (in one eye only) in 70 percent of cases. Optic Neuritis (ON) is an inflammation, with accompanying demyelination, of the optic nerve serving the retina of the eye. It is a variable condition which is experienced as a temporary loss or disturbance in vision, along with possible pain behind the affected eye. Optic neuritis most often causes a large, noticeable "blind spot" in the center of the visual field. The person experiences a dark, clouded area in the middle of their view (see image right). This is called central scotoma.
It can also cause any of the following symptoms:
- blurring of vision
- double vision
- loss of visual acuity
- loss of some or all color vision
- complete or partial blindness
- pain behind the eye or with eye movement
Most typically, optic neuritis first affects people aged between 15 and 50 years of age. In this age group, studies indicate that more than 50 percent of patients will convert to Multiple Sclerosis within 15 years. As with MS, women are about twice as likely as men to present with ON and the prevalence in Caucasian people is higher than in other racial groups.
Although episodes of optic neuritis typically resolve spontaneously, either partially or completely within a few weeks, acute loss of vision can be treated with high-dose corticosteroids such as methylprednisolone (Solu-Medrol®) or dexamethasone (Decadron®). If visual loss is relatively mild and manageable, the best alternative is probably to wait for the episode to remit on its own. While it is very rare for a person with MS to completely lose their sight, it is not uncommon for a person to experience recurring episodes of optic neuritis.
Diplopia
Diplopia (double vision), seeing two of everything, is caused by weakening of eye muscles, and occurs when the pair of muscles that control a particular eye movement are not perfectly coordinated. When the images are not properly fused, the person perceives a false double image. Double vision may increase with fatigue or overuse of the eyes (e.g., with extended reading or computer work), and improve with rest. Resting the eyes periodically throughout the day can be beneficial.
Diplopia usually resolves without treatment. In some cases, it is treated with a short course of corticosteroids. Temporarily patching one eye while trying to drive or read will also stop the double image; however, the brain's ability to accommodate the weakness and produce a single image in spite of the weakened muscles is remarkable so patching should not occur over extended time periods. Special lenses are rarely recommended because the symptom tends to be transitory.
Nystagmus
Another relatively common visual finding in MS is Nystagmus, uncontrolled horizontal or vertical eye movements in one or both eyes. Nystagmus may be mild, only occurring when the person looks to the side, or it may be severe enough to impair vision. It does not always cause noticeable symptoms, and is a painless problem. Some drugs and special prisms have been reported to be successful in treating the visual deficits caused by nystagmus and a related eye movement disorder, opsoclonus, which causes "jumping vision."
Ocular Dysmetria
Ocular dysmetria involves the constant under- or over-shooting of the eyes when attempting to fix your gaze on something. It is a rather upsetting nausia-inducing condition that makes you want to close your eyes to avoid it. Ocular dysmetria indicates lesions in the cerebellum which is the brain region responsible for coordinating movement. It is a symptom of MS, along with several other neurological conditions.
Internuclear Ophthalmoplegia
Internuclear Ophthalmoplegia (INO) is a disorder of eye movements caused by a lesion in an area of the brain called the medial longitudinal fasciculus (MLF). INO is associated with uncontrolled eye movements in one eye when the other one moves outwards. It can also, but not always, cause double vision, or diplopia. Multiple Sclerosis is the most common cause of internuclear ophthalmoplegia and in MS it is usually unilateral (occurring in only one eye); however, there are other causes including cerebrovascular problems (usually in older people) and HIV infection.
Phosphenes
Phosphenes are brief spots of light brought on by eye movement (movement phosphenes) or sudden noises (sound phosphenes) which last for less than a couple of seconds. Such phosphenes are often associated with Optic Neuritis and are caused by mechanical aggravation of a damaged or inflamed optic nerve. In optic neuritis, movement phosphenes are usually brought on by side-to-side movement of the eye. Movement phosphenes can sometimes be induced weeks or months after vision has all but completely recovered, but it is rare for them to continue for a year after the initial attack of optic neuritis.
Afferent Puillary Defect
Afferent Pupillary Defect (APD) or Marcus-Gunn pupil is a condition of the eye where the pupil doesn't dilate appropriately to the level of light reaching it. This will often result in one pupil appearing larger than the other (relative afferent pupillary defect - RAPD). This person with APD is often unaware of it except by looking in a mirror. There are many causes of APD including optic neuritis (ON), glaucoma and optic nerve tumor. In multiple sclerosis, APD, is usually associated with damage to the optic nerve resulting from ON.
The eye in which the ON has occurred acts as if it is in a lower light situation than it really is and dilates more so that it can let more light hit the retina.
Questions?
National Multiple Sclerosis Society, Ohio Buckeye Chapter
6155 Rockside Road, Suite 202
Independence, OH 44131-22117
(800) 667-7131
Visit National Multiple Sclerosis Society's website for more information about multiple sclerosis.