WHAT IS PHOTOSENSITIVE EPILEPSY?
Flashing or flickering lights, or even geometric shapes or patterns can sometimes trigger seizures. This fairly rare condition is known as photosensitive epilepsy.
HOW MANY PEOPLE ARE PHOTOSENSITIVE?
Approximately 1:130 of the general population has epilepsy and of these only a few per cent may have seizures induced by flashing lights. Such sensitivity is commoner in children and adolescents and becomes less frequent with age, being very uncommon from the mid twenties onwards.
HOW CAN I TELL IF I AM PHOTOSENSITIVE?
Most people are aware of this. A standard EEG is done with photic stimulation i.e. flashing light and photosensitivity would usually be diagnosed at this stage.
WHAT FACTORS MAY TRIGGER A SEIZURE IN SOMEONE WITH PHOTOSENSITIVE EPILEPSY?
Common triggers include:
- Viewing a television screen, playing a video game/using other computer graphics
- Having a faulty television or other light source which flickers at a slow frequency
- Sunlight through a line of trees
- Looking out of a window in a train
- Sunlight on water
- Stroboscopic lights
- Looking at a moving escalator
Sometimes people are also sensitive to various geometric shapes or patterns, for example, stripes or checks.
- the frequency of the stimulus
- the intensity of the stimulus
- the background illumination
- the wave length of the light
WHAT FREQUENCY OF FLASHING LIGHTS IS MOST LIKELY TO TRIGGER A SEIZURE?
The frequency of flashing light, which is most likely to provoke seizures, varies from person to person. Generally, it is between the frequencies of 5-30 flashes per second (hertz). Some people, however, are photosensitive at higher flash frequencies. It is uncommon to have photosensitivity below 5 hertz.
CAN VDUs CAUSE A PROBLEM IN PEOPLE WITH PHOTOSENSITIVITY?
VDUs usually operate at a sufficiently high frequency that they do not provoke seizures, even in people with photosensitivity. Nevertheless, there are rare examples of people with sensitivity to high flash frequencies. In general terms, it is better if the lighting in the room is with an ordinary light rather than a fluorescent tube, as the flicker frequency from the fluorescent tube could potentially interact with the flicker frequency from the VDU. Probably, what matters more is what is showing on the VDU, in other words, is one looking at a flickering programme or changing geometric pattern on the screen?
WHAT ABOUT COMPUTER GAMES?
Playing computer games very rarely triggers epileptic seizures in people without a known history of epilepsy. People who do have a seizure for the first time when playing video games usually have an unrecognised susceptibility to seizures triggered by flashing light, that is, most of them are photosensitive.
It is important to realise that epilepsy is common and that one should not be surprised that seizures will sometimes occur by chance whilst someone is playing an electronic game or watching TV, without any causal link. Proper investigation is required to determine the true cause of a presenting seizure in order to give appropriate medical advice.
CAN MY CHILD GO TO DISCOS?
Ordinary coloured lights do not usually cause a problem if they do not flash, however, stroboscopic lights can trigger seizures, particularly if the background illumination is low and there may be other environmental triggers e.g. stress, excitement, tiredness etc. Some local authorities do have rules concerning the flash frequency of strobe lighting. The local Environmental Health Department will be able to give you more information on this. Unfortunately, if a person is known to be photosensitive it may be best to avoid stroboscopic lights.
- Seek individual advice from your specialist as the risks of seizures vary from person to person.
- Covering or shutting one eye may reduce the effects of a flashing or flickering light if you are suddenly/unexpectedly exposed to a flickering light source.
- Change channels on the TV using a remote control to avoid going too close to the screen.
- Avoid looking at poorly tuned channels or faulty TVs.
- Consider using a high frequency (100hertz) TV or one with a smaller screen.
- Wearing sunglasses can reduce glare.
- Avoid pastimes that require close exposure to electronic screens, especially if they are large or involve the use of standard TV screens (e.g. playing video games).
- It is rare for seizures to be triggered by film in a cinema or hand held miniature screens.
- Excess tiredness may increase the risk of photosensitive seizures.
- It is important not to put blanket restrictions on all people with epilepsy presuming that they are photosensitive. This condition is relatively rare and unnecessary constraints on people’s lifestyles must be avoided.