Photosensitive Epilepsy

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What is photosensitive epilepsy?

To some degree, we all find flickering lights or some colours or patterns irritating or difficult to look at, but in some people with epilepsy, seizures are actually triggered by flashing or flickering lights, or by certain geometric shapes or patterns. People who have these seizures are diagnosed with photosensitive epilepsy.

Photosensitive epilepsy is a type of epilepsy we call reflex epilepsy and is seen in less than 5% of people with epilepsy. It is when seizures are triggered by flashing or flickering lights, or by certain geometric shapes or patterns.

These seizures are more commonly linked with the generalised onset epilepsies than with focal onset epilepsies, and because they are usually triggered by visual stimulation, seizures can be reduced by making efforts to avoid the triggers. The person may also have other seizures not triggered by visual stimulation.

Although prognosis is generally very good, photosensitive seizures may persist. Medication and avoiding visual triggers can help gain seizure control.

How do I know if I have photosensitive epilepsy?

Some people only have photosensitive seizures, while others may have other seizure types as well as photosensitive seizures. It is important to have a clear diagnosis, and keep good records or a seizure diary to help differentiate the seizures and their triggers.

Photosensitive epilepsy can be diagnosed by having a routine EEG with strobe (flickering) light or pattern stimulation. A routine EEG should include this.

Today’s lifestyle can involve spending many hours using (visual) technology. While a seizure may occur in these conditions, it may also be a spontaneous or chance event – so don’t conclude your seizures are photosensitive seizures just because you had one or two when using technology.

How is it treated?

In most cases the photosensitive seizures can be well controlled by antiepileptic medication and avoiding known triggers.

What are the triggers?

Our modern environment is a rich source of potentially seizure-triggering visual stimuli. Typical sources can include:

  • strobe, flickering or disco lights
  • televisions (TV’s), computers, electronic/videogames
  • Venetian blinds, striped walls or clothing
  • moving escalators
  • sunlight reflected off snow, sea or water or interrupted by trees during a ride in a vehicle

Less common stimuli are:

  • rotating helicopter blades
  • faulty flickering fluorescent lights
  • welding lights

New potentially provocative sources turn up now and then unexpectedly.

What are other factors involved?

Whether or not a photosensitive seizure happens is also influenced by:

  • whether the eyes are open, closed or closing at the time of the stimulation
  • the speed or flicker of the flashing (light)
  • the contrast and brightness of the stimuli – in general, with brighter stimuli and strong contrasts in colour, the more likelihood of inducing seizures
  • how long the stimulation goes for – a seizure is more likely to occur with longer exposure
  • the colour of the flicker (if any) – red flicker is more provocative and colour oscillating from red to blue
  • how large and close the screen is – the larger and closer someone is, the more “field of view” it takes up and is more likely to trigger a seizure

Managing photosensitive epilepsy

Types of stimuli that may trigger a seizure

Avoiding sources of triggers is the best advice. The following precautions only apply to those people who are diagnosed with photosensitive epilepsy.

Television: There are so many different types of television technology now, and modern television screens are much less likely to trigger seizures. However, it is important to keep a good distance from the screen. Seizures may be provoked by the images and colours (especially flashing or alternating) on the screen rather than the screen itself. So the further back a person sits, the less likely a seizure will occur.

Note: Older-style TVs use cathode ray tube (CRT) technology. It is common for people with photosensitive epilepsy to be sensitive to this flicker rate, so sit well back from this television type to reduce the risk of seizures. Newer CRT’s now flicker at a much faster rate, almost undetectable by the human eye and outside the most common sensitivity for triggering seizures. Therefore they are much less likely to trigger seizures.

Monitors have been flickering for many years. An older style cathode ray tube (CRT) monitor created its picture with flicker and if you are very close to the screen, you can see the flicker. But it can also happen on modern PC monitors. Even though you can’t see them flicker, an “invisible” flicker is present all the same.

Television images: It is more likely the images are what provokes a seizure, such as flashing sequences or rapid changes from light to dark or to contrasting colours, e.g. from red to blue.

Tips:

  • Sit at least 2.5 metres from the television screen in a well-lit room
  • Sit at an angle rather than directly in front of the screen
  • Place a lamp on or behind the television to reduce the contrast between the screen and the surroundings, even when watching during the day
  • Use a remote control or cover one eye to lessen the effect of the flicker when manually changing settings
  • Do not watch the screen when fast forwarding, rewinding or adjusting the vertical hold
  • In the cinema, try to sit well back from the screen and near a light source, such as in an aisle seat where there is a guiding light
  • Look away from any content that makes you feel uncomfortable
  • A smaller screen set at low brightness and contrast is preferable.

Electronic and video games: Apart from the TV or computer screen itself, the content/images of the electronic or videogames are important; some being more likely to provoke a seizure than others. Other factors may play a role, such as the distance to the screen is shorter in videogame playing than in watching a TV program, and children who play these games for extended periods can suffer visual tiredness, eyestrain and sleep deprivation, which can also contribute to seizures.

Usually these games are only likely to trigger seizures if there is an underlying tendency to do so – if it has happened to you before. Generally, a seizure is most likely to occur within the first 30 minutes of play. Prolonged play can be associated with tiredness and sleep deprivation – which is a known trigger for seizures.

Tips:

  • Sit as far away from the screen as possible
  • Play the game in a well-lit room and reduce the brightness of the display
  • Avoid continuous exposure to the same pattern and don’t play when overtired
  • Check games for epilepsy or seizure warnings
  • If you do find that a game(s) makes you feel like you are going to have a seizure, then it is best to stop playing and keep exposure to the game in short bursts (have a break every 10-15 minutes) or avoid that particular game altogether.

It is good to take breaks from any electronic games and refresh.

Computer monitors: Computer screen or images on computer screens also have  potential to trigger a seizure, but this is uncommon. Only in exceptional cases would it be necessary to restrict computer work. If you are sensitive to screen flicker on older monitors, a screen filter may help. You could always try an anti-glare filter to reduce screen glare. High quality monitors, liquid crystal or LCD screens with a flicker (refresh) rate of at least 60Hz may not pose a problem. Once again, it is more likely to be the images on the screen that may cause a seizure.

It is uncommon for seizures to be triggered by hand-held screens.

3D movies: There is much hype and concern about the effect of 3D movies being a seizure trigger, but this is not the case. In people with photosensitive epilepsy, the risks of a seizure being triggered by 3D movies is no greater than conventional 2D programmes. For people with non-photosensitive epilepsy the risk of 3D movies triggering a seizure is negligible.

Lights: The frequency of a flashing or flickering light most likely to trigger seizures will vary from person to person. Generally it is between 8-30 flashes per second (Hz), but this can vary. Many people seem to be sensitive around 15-20Hz. Again, it is also dependent on the brightness and intensity of the light, and how long the person is exposed to it.

Fans: Ceiling fans in a lit room can create a flicker effect. A pedestal fan is best if you feel the ceiling fan may trigger a seizure.

Geometric patterns: Some people are sensitive to geometric patterns which have strong contrasts of light and dark such as stripes or checks. Some of these patterns can create an optical illusion. Some buildings and public places may have large areas like this, such as carpet. The average person will just feel some visual distortion, but if you feel strange in this environment, it is important to leave or at least cover one eye.

These patterns may also be on a television or computer screen, or something in the natural environment, such as sunlight through trees, or through Venetian blinds. Such contrasting patterns are more likely to be a trigger if they are moving, changing direction or flashing, rather than if they are still.

Camera flashes: These rarely trigger seizures unless fired in rapid succession.

Red flickering light and strobe/disco lights: These can trigger seizures, particularly if the room is darkened and there are other triggers such as stress, excitement, tiredness, sleep deprivation and alcohol. For those who are photosensitive, the risk will greatly depend on the speed of the flashing light.

Tip:

  • It is sensible to avoid disco’s if you have photosensitive epilepsy, but this is a common social activity for young people, so it may be a hard one to resist. Some people do attend discos even if they are photosensitive, and find they can tolerate it. Responsible clubs and DJs may display warnings if these lights are used and retail employers may turn off flashing lights in their store if requested.

Sunlight: This can trigger seizures in a number of ways such as: the reflection of light flickering off water or through leaves of trees, and light flickering through posts or railings when moving quickly, e.g. walking past or travelling in a car. Some people may even be affected by looking outside through a screen door.

Tips:

  • Cover one eye with the hand to lessen the effect of the flicker as binocular (looking through both eyes) vision is needed to trigger a seizure.
  • Polaroid sunglasses with shaded sides may also help reduce the risk.

Treatment

Knowing what sources may trigger your photosensitive seizures, and reducing your exposure to them plays a significant role in reducing or stopping this type of seizure. Some people may need medication and the choice of medication depends on the type of epilepsy related to the reflex epilepsy.

Tips:

  • Avoid discos
  • Avoid video games with high contrast flashing and have frequent breaks if playing video games
  • Cover or patch one eye if you cannot avoid certain sources of stimulus (eg travelling in a vehicle when sunlight is flickering through the trees)
  • Wear glasses that reduce the amount of light as much as possible, such as polarised sunglasses
  • Blue lenses, (type Zeiss Clarlet F133 Z1), have proven effective for many people
  • Use smaller TVs and computer screens. Ask about specific computer screens when purchasing a computer
  • Reduce the contrast of TV and computer screens
  • Use a remote control
  • Keep a good distance to any screen (ideally at least three times its width)
  • When using any screen, keep the room well lit.

These are general suggestions, and depending on your sensitivity, not all approaches may be necessary or effective.

For more information go to:

Factsheet: Photosensitivity

What is photosensitive epilepsy (video 1:34)?

How video games can cause seizures (video 3:14)

Reflex epilepsies

3D films and epilepsy