Vision problems are among the commonest symptoms of multiple sclerosis (MS), resulting from damage to the myelin sheath around nerves in the eye.
These are often the first symptoms to be noticed: blurred or double vision, red-green colour distortion, eye pain, blind spots or even temporary loss of vision. (Although MS rarely produces complete blindness.) While this is alarming, most people recover well.
There are several different kinds of MS-related visual disturbance:
• Optic neuritis is the most frequent problem. It occurs when there’s inflammation or damage to the nerves that control eye movement and coordination.
Many people experience blurred or greying of vision, and some will develop blindness in one or both eyes. The condition can be painful, especially when you move your eyes, causing sore eyes or headaches. Colour perception (especially red) may be reduced. A dark spot might appear in the centre of the visual field, and there may be “flashing” sensations. Symptoms may worsen with heat or exhaustion.
The severity of this damage varies. In most cases, it goes away spontaneously. Improvement usually occurs within three to five weeks, and may continue for a year. Complete recovery is common. However, if the nerves are badly damaged and attacks recur, there may be long-term visual impairment.
Corticosteroids, usually intravenous, reduce inflammation and shorten the length of the optic neuritis attack. Beta interferons can reduce recurrences. Vitamin supplements may also aid recovery.
• Nystagmus is the name for involuntary eye movements: usually side to side but sometimes in a vertical or circular direction. Almost always, both eyes move together.
This common symptom is often so mild as to be unnoticeable to the person with MS, but can be severe enough to affect their vision. If it continues, it may make them feel dizzy, unbalanced or nauseous. Many find that, if they keep their eyes at a certain angle, nystagmus is reduced and vision improved. Because of this, they may hold their head in a particular position.
If nystagmus is causing real impairment, certain immune-system drugs and steroids may be of benefit. Botox (a muscle relaxant) injected into the eye muscles may help, although this only works for a few months and the procedure requires general anaesthesia. On the whole, nystagmus can be hard to treat.
• Diplopia – double vision – is an early symptom of MS that often goes unrecognised. It occurs when the pair of muscles that control an eye movement become weak and uncoordinated. Loss of balance may result.
Diplopia may appear quite suddenly, is usually temporary and will improve without intervention within weeks or months.
It can be exacerbated by tiredness or overuse of the eyes (e.g. reading off a screen), and often improves with rest. A course of corticosteroids may also be beneficial. A patch over one eye may help with driving or other short tasks, but shouldn’t be used for long periods. In some cases, special prismatic lenses may be recommended.