08 October 2004

Photosensitive epilepsy

You have photosensitive epilepsy if your seizures are triggered by exposure to flashing or flickering light.

You have photosensitive epilepsy if your seizures are triggered by exposure to flashing or flickering light. Although it is widely believed that all people with epilepsy are photosensitive, in fact this is true for only about 3 - 5%. Photosensitive epilepsy is most common in children and teenagers.

Seizures in photosensitive people may be triggered by exposure to such light sources as television screens (especially those that flicker or images that "roll"), certain computer or arcade games, alternating patterns of different colours, flickering fluorescent tubes and flashing strobe lights such as those used in fire alarms or nightclubs. Sometimes seizures are triggered by natural light, for example sunlight flickering through trees or railings when you move rapidly past them, or light reflecting off water. The most common trigger culprit, however, appears to be television screens.

The light sources mentioned above will not invariably induce seizures in a photosensitive person; there are various contributing factors, which include:

  • the frequency of the flashing or flickering light (how quickly the light flashes). Frequencies between 5 to 30 flashes per second (hertz) are most likely to trigger seizures, although this varies among different individuals.
  • brightness of the flashing light
  • the level of background lighting

The likelihood of flashing lights such as those used on emergency vehicles triggering seizures is considered to be small, because the distance between the light source and the viewer is usually quite large.

It is likely that you will be tested for photosensitivity when you are initially diagnosed with epilepsy. During the electroencephalogram (EEG) test, the electrical activity in your brain is recorded while you are exposed to flashing lights at various intensities.

Avoiding light-induced seizures
If you have photosensitive epilepsy, your doctor may advise you to avoid exposure to certain types of flashing lights, and to avoid places or activities where flashing lights are likely to be encountered (such as nightclubs). The following measures may also be helpful in reducing the incidence of light-induced seizures:

  • Cover one eye and turn away from the direct light source when in the presence of flashing lights.
  • Ask your doctor or optician about photochromic (light responsive) glasses. These glasses, worn with one lens darkened, render 95% of photosensitive people safe from light-induced seizures. 
  • Wear good polarised sunglasses outside can help reduce flickering reflections.
  • Watching television (or playing computer games using a TV monitor):
    • Watch TV in a well-lit room and adjust the brightness of the set, to reduce the contrast between light from the screen and its surroundings. 
    • Sit as far back from the screen as possible (at least 2.5 metres).
    • Consider using a smaller screen.
    • Avoid watching for long periods of time. Don't watch TV for longer than 30 minutes without taking a break of at least five minutes. Look away from the screen every now and then while you're watching.
    • Avoid looking at poorly tuned or faulty TVs.
    • Use the remote control to adjust or change channels so you won't have to get too close to the screen. If you do approach the screen, cover one eye.
    • Don't watch TV if you are tired or under the influence of alcohol. 
  • Using computer monitors:
    • Most current computer displays have scan frequencies of 60 per second and above, which are unlikely to provoke seizures. The risk of a seizure depends on the material being displayed - certain computer games, for example.
    • Use a flicker-free monitor (liquid crystal or flat screen).
    • Reading from the screen for a long time can tire the eyes and this could provoke a seizure in some people. Anti-glare screens do not reduce flicker rate, but help for eyestrain and tiredness.
    • Take frequent breaks.

Read more:
The outcome of epilepsy


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