Photosensitive epilepsy (PSE) describes a sensitivity to flashing or flickering lights, as well as certain geometric patterns or glare. These may be found coming from television sets, computer screens, disco lights and even natural light sources, such as sunlight shining on water or through trees. Such lights may provoke a seizure.

However, only about 3-5% of people with epilepsy are photosensitive. As a result, the vast majority of people with epilepsy do not need to avoid these flashing lights. Even most of those who are photosensitive can still watch television and use computers for example if they follow certain guidelines.

PSE is diagnosed by EEG and those affected are advised accordingly.

If a seizure does occur because of PSE, in almost all cases, it will be a generalised tonic-clonic seizure (the person will become rigid and will then fall to the ground, where there will be jerking/convulsing of all four limbs). Generally the seizure will occur at the time that the person sees the light/flashing, rather than later on.

Who is most commonly affected by photosensitivity?
Photosensitivity most commonly affects children. It usually becomes evident between the ages of six and 15, suggesting a link with early puberty. There is some evidence to suggest that photosensitivity can disappear with age. Girls are more affected than boys.

What are the guidelines in relation to watching television?
Since the 1950s, television has been the most commonly reported trigger of seizures among people with PSE. Originally it was thought that this was because television sets were faulty. However, it is now thought that the main reason is due to the nearness of the television set.

The closer a person is to a television, the more the screen fills their entire field of vision and the greater the effect of the flicker frequency of the picture. Other factors can also contribute to the risk of a seizure in someone watching television, such as tiredness and alcohol.

A few simple procedures to minimise or avoid the risk of a seizure when watching television are:
Be seated at least 3m/10ft from the TV set. A lamp should be placed on top of the set to counteract the brightness on the screen
Use the remote control to change channels, rather than having to go close to the television screen
If you have to go near the screen, e.g. to turn it on, place a hand over one eye and this will lessen the effects by 50%.

If you are buying a new television set, remember that while most European sets are 50 hertz, it is possible to get 100 hertz sets. (Hertz is a unit of frequency. The slower the frequency, the more flickering will occur.) One hundred hertz sets are standard in America and do not cause the problems associated with low flicker rates. Liquid crystal display (LCD) screens are flicker-free.

Remember the larger the television set, the more likely the image is to fill the entire visual field. While widescreen TVs are popular, the characteristics and size of these sets may prove problematic for susceptible individuals. A smaller, higher hertz or LCD television set should be considered therefore.

The position of the TV set is also important if a seizure does take place. Where possible, the set should be mounted on the wall, as free standing sets could be knocked over during a seizure. Wires and flexes should also be kept to a minimum and ideally tacked to the wall or skirting board.

Computer screens
There is no evidence to suggest that computer screens/visual display units (VDUs) cause epilepsy, but seizures may be provoked in a very small number of people who are sensitive to the flicker and glare effect of the screen. However most people should be able to use VDUs safely if they are careful.

A screen filter should be used to reduce glare and the rate of flicker should be adjusted to a safer range. Similar to television sets, LCD VDUs should be used if possible. These are flicker-free and therefore may pose less of a risk to a person with PSE. (Even with some LCD screens however, an attachable anti-glare screen may be required if this measure is not built in.) Remember to always take frequent breaks from the screen and avoid becoming overtired.

Generally there are fewer problems with newer equipment.

Video games
Current evidence suggests that video games do not induce an epileptic seizure, where such a tendency does not already exist. However, computer software or video games featuring patterns of flashing lights or geometric patterns may trigger seizures in a very small number of sensitive people.

The reaction that a photosensitive person has to a particular game depends on the nature of the flickering light or pattern featured, combined with glare and the proportion of the visual field that the image occupies.

Similar to the use of VDUs, you should not play video games if you are overtired.

Disco lights
A person with PSE may find that the strobe lighting sometimes used in discos/nightclubs can trigger a seizure. If this is the case, clubs that use this type of lighting should be avoided.

As the vast majority of people with epilepsy are not photosensitive, this should not be a problem for most. However, if you are photosensitive and strobe lighting comes on suddenly, cover one eye with your hand and move away from the lights. Closing your eyes will be of no benefit, as the light will penetrate the skin of the eyelids.

For further information about epilepsy contact:
Mail: Brainwave, The Irish Epilepsy Association, 249 Crumlin Road, Dublin 12.
Phone: 01-455 7500
Email: info@epilepsy.ie
Website: www.epilepsy.ie

Become a member of Brainwave here

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