Bright Sight

Oliver Backhouse, Consultant Eye Surgeon www.cataract.org.uk

Optic Neuritis

1] What is Optic Neuritis?

Optic neuritis is the most common cause of sudden visual loss among young people. It is often associated with discomfort in or around the eye, particularly with eye movement. The optic nerve is like a cable of electric wires, and consists of more than one million separate tiny wires or nerve fibres. Each nerve fibre carries a part of the visual information picture (or image) we see to the brain. If some or all of the nerve fibres become inflamed and do not function properly, vision becomes blurred.

With optic neuritis, the nerve tissue becomes inflamed and the nerve fibres do not work properly. If many of the nerve fibres are involved, vision may be very poor, but if the optic neuritis is mild, vision can be nearly normal. For most people with optic neuritis, vision will improve (though not always quite back to normal) without treatment.

2] What causes Optic neuritis?

It is not entirely clear what causes optic neuritis, though it is generally suspected that autoimmune disease and / or previous viral infection may play a role. In the most common form of optic neuritis, the optic nerve is attacked by the body’s overactive immune system. In children especially, optic neuritis develops following a viral illness such as mumps, measles or colds. In some parts of the world poor nutrition and/or other infections may be the cause.

3] What are the symptoms of Optic Neuritis?

Optic neuritis usually develops over a few hours to days. One may notice the following symptoms:

  • Blurred vision in one eye or both, especially after exercising or a hot bath. The blurring may be like a blob of grease in one area or it may affect the whole picture in one eye.
  • Vision is dim, as if the lights are turned down.
  • Colours appear dull or faded.
  • Pain behind the eye, particularly when moving the eyes.

A careful description of these symptoms is important to your Ophthalmologist in diagnosing optic neuritis since the eye often looks perfectly normal. A medical exam will be performed because optic neuritis can be confused with many other causes of poor vision. Optic neuritis may recur in the same eye or the other eye.

4] How is Optic Neuritis diagnosed?

The Ophthalmologist will measure your vision, examine how your pupil reacts to light and inspect the inside of your eye. Other tests which may be performed include colour vision and visual field testing.

5] How is Optic Neuritis treated?

Fortunately over 90% of people recover their vision without any treatment, generally over a period of weeks to months. Some may have residual ‘washed out’ vision and have disturbances when exercising or taking a hot bath. This is related to the damaged myelin (insulation) that surrounds the nerves. It often settles with time and patients who notice this problem are not more likely to get worse.

Research has shown that patients who are treated with high dose steroids have their vision restored more quickly than those patients who are not treated by 2 weeks. However both groups of patients ultimately are shown to recover to the same level of vision.

6] Conditions which can be confused with optic neuritis

The optic nerve can be affected by other disorders such as lack of blood, (ischaemia) or by compression by swellings of various types. There are also some rare genetic conditions which can damage the optic nerves. If the patient has atypical symptoms or if the optic neuritis is associated with other eye or neurological signs a detailed scan of the eye or brain may be performed as well as some blood tests. While some of these brain scans may show inflammation in other areas of the brain, this does not necessarily require treatment if it is not causing any problems. Treatment is currently withheld unless there is obvious progression over a period of time. This is because of: 1) The excellent recovery expected without any treatment; 2) The fact that all medications do have potentially serious side-effects and 3) In that what is seen on a brain scan has not been clearly identified as causative regarding the prediction of a patients possible future symptoms. Some of the medication being used is very new and still experimental. Should there be a recurrence or later development of other neurological symptoms, some of these medications may be offered to you.

7] Does Optic Neuritis come back?

Most people who have ON will never have another episode but recurrences (second attacks) can occur, either in the same eye or in the other eye. They are treated in the same way as the first attack with steroids being offered. Some patients who have had optic neuritis may be likely to have other episodes of inflammation in other parts of the nervous system. These episodes can cause all kinds of different symptoms and are usually sorted out by the general practitioner who can then refer the patient to an appropriate specialist, usually a neurologist. There is no special treatment or diet etc that someone with optic neuritis should take to avoid such episodes in the future.

What caused this to happen?

We do not have a complete understanding of optic neuritis. It is likely that it represents a combination of a particular form of immune system reaction with a previous stimulation possibly by a virus.

What is going to happen to my vision?

In the vast majority of patients, your vision will improve. It may not improve to normal, but it is likely that there will be a sustained improvement whether or not you are treated.

Can treatment with steroids make this better?

Treatment with steroids has been demonstrated to accelerate recovery but it will not on average change the ultimate level of recovery. We have no way to guarantee that vision will recover and in some patients it will not.