PHOTOSENSITIVE EPILEPSY

by Epilepsy Association of Scotland

Photosensitive epilepsy is an uncommon condition, in which flashing or flickering lights, usually of high intensity, and/or certain patterns (such as stripes), trigger off epileptic seizures. It is sometimes called "reflex epilepsy".

Prevalence

One person in every two hundred is diagnosed as having epilepsy, whereas only one in about every ten thousand has photosensitive epilepsy. Among people with epilepsy only an estimated 2% - 5% have seizures triggered by light or patterns. However, the incidence does vary slightly in different ethnic groups. A diagnosis of photosensitive epilepsy can only be made by carrying out an EEG recording with photic (flickering) light or pattern simulation. If you are uncertain whether or not you have photosensitive epilepsy, you should seek advice from your doctor.

Photosensitive epilepsy most commonly affects children. The age of onset is usually between 9 and 15 years. It is rare to have a first seizure due to photosensitivity before the age of 5 or after the early 20s. Girls are affected more often than boys.

Some photosensitive people have seizures only when they are exposed to a flashing or flickering light source, or to certain patterns. Others may have spontaneous seizures, as well as seizures due to photosensitivity.

Types of seizure

Seizures may vary from person to person, but are most often generalised tonic clonic attacks (major convulsive seizures), absence attacks, and myoclonic jerks.

Diagnosis

A diagnosis of photosensitive epilepsy can only be made by carrying out an EEG recording with photic (flickering) light or pattern simulation. It is essential to obtain an expert diagnosis, since there is a danger that people with epilepsy who are not photosensitive will falsely assume that they are, and quite unnecessarily restrict their lifestyle. Many hours each week are spent at work or at home watching television, playing video games, or using visual display units. A seizure may occur in one of these circumstances, but it may be a spontaneous or chance event. It does not necessarily mean that the television, video, or visual display unit has triggered the seizure.

Treatment

Anti-epileptic medication, often sodium valporate (Epilim), may be prescribed to reduce the risk of seizures. In some cases of photosensitive epilepsy, medication may not be necessary at all, but a doctor's advice must always be sought as to whether or not treatment is required.

Triggers

There are various factors that may trigger seizures in photosensitive people.

Both artificial and natural light sources can trigger seizures. Sometimes the frequency of the flash is the trigger. Different people are affected by different flash frequencies. The intensity of the light can also be a key factor. For example, sunlight shining off water or through the leaves of trees, or flickering through trees or railings can cause seizures, as can sunlight on rotating helicopter blades. Polarised sunglasses, preferably with side shades, can help to reduce the flicker effect.

Television is the most commonly reported trigger of seizures in photosensitive people. Neither the faulty functioning of TV, nor the usual movement of images on the screen, seems to play any significant role in provoking epileptic seizures. The distance of the person from the TV screen is the most important factor. The closer the person is to the set, the more the screen fills the entire field of vision, and the greater the effect on the retina of the flicker frequency of the picture. Tiredness and alcohol can be associated factors. A few simple precautions can be taken as follows:

• sit at least three metres away from the set
• sit level with, not below, the screen
• place a subdued light on top of the set to counteract the brightness of the screen, even whilst watching during daylight hours
• place a hand over one eye to lessen the effect of the flicker when operating the controls of the TV, since binocular (both eyes) vision is needed to trigger a seizure

A small TV screen is preferable to a large one.

Most young people with epilepsy are not photosensitive and can enjoy discos, although excessive heat and noise may be factors that will trigger a seizure. For the small minority with photosensitive epilepsy, the degree of risk depends on the speed at which the lights are flashing.

Current medical opinion is that video games do not create a tendency to epileptic seizure when the tendency is not already there. However, games featuring patterns of flashing lights can cause isolated seizures in a very small number of photosensitive people, depending upon the nature of the flickering lights featured. It is also possible that sustained and intense concentration whilst playing video games may generate stress, which in turn may trigger a seizure.

There is no evidence to suggest that VDUs can actually cause epilepsy. Epileptic seizures may be provoked in a very small number of people who already have a sensitivity to the flicker-effect of the screen. Computer work should rarely be a restricted occupation for people with epilepsy, although sustained and intense concentration may be stressful, and may trigger a seizure. It is possible to get a screen cover to minimise flicker. Also, some screen background colours are preferable to others (e.g. green).