For about 1 in 4,000 of the population, exposure to flashing lights at certain intensities or to certain visual patterns can trigger seizures. This condition is known as photosensitive epilepsy.
The onset of Photosensitive epilepsy is most common in children and adolescents, especially those with generalized epilepsy, in particular juvenile myoclonic epilepsy. It becomes less frequent with age, with relatively few new cases in the mid twenties.
Many people are unaware that they are sensitive to flickering lights or to certain kinds of patterns until they have a seizure. They may never go on to develop generalised epilepsy, which is characterized by recurrent spontaneous seizures, though a seizure may still be triggered by certain photic conditions. Many individuals who are disturbed by light exposure do not develop seizures but experience other symptoms such as headache, nausea, dizziness and more. They do not have epilepsy.
Photosensitive epileptic seizures can, as in generalised epilepsy, take many forms ranging from short-lived “absences” to classic tonic-clonic events with spasms and uncontrolled physical movements. Seizures can be terrifying for the individual, deeply distressing for families and friends and profoundly life changing for all concerned. As well as emotional distress, seizures also carry inherent and situational risks which often include physical harm and can and have lead to loss of life. There is also growing evidence that the brain trauma involved in all seizures can result in long term socio-psychological damage.
It is the duality of the presence of dormant photosensitives (you only know you are photosensitive when you have a seizure) and the potential for harm that makes it so important to try to remove potential seizure triggers.
Examples of Triggers
Seizures in photosensitive people may be triggered by exposure to television screens due to the flicker or rolling images, to computer monitors, to certain video games or TV broadcasts containing rapid flashes or alternating patterns of different colours, and to intense strobe lights like visual fire alarms. Certain visual patterns, especially stripes of contrasting colours, may also cause seizures.
Seizures may also be triggered by natural light, such as sunlight, especially when shimmering off water, flickering through trees or through the slats of Venetian blinds.
Not all televisions, video games, computer monitors, or strobe lights trigger seizures, even in predisposed individuals several factors must combine to trigger the photosensitive reaction.
- the frequency of the flashing (that is, how quickly the light is flashing)
- the brightness of the flashing
- the contrast with background lighting
- the distance between the viewer and the light source
- the wavelength of the light
- whether a person’s eyes are open or closed at the time
The frequency or speed of flashing light that is most likely to cause seizures varies from person to person. Generally, the flashing most likely to trigger seizures is between the frequency of 5 to 30 flashes per second (Hertz).
To be safe, photosensitive individuals are advised to keep at a distance from TV screens and to place other lights in the surrounding area to lower the contrast between the brightness on the screen and the background. These conditions help protect the viewer and are easy to obtain during TV viewing but not when randomly exposed to strong environmental lights. Therefore, other protective devices or strategies may be needed.
If you have already been diagnosed with a generalised epilepsy condition, check with your doctor if you are concerned about flashing lights triggering seizures. Chances are that your medical records will indicate how you responded to flashing lights during the electroencephalogram (EEG), a test done routinely in most people with epilepsy. During this test, sensors are attached to the patient’s scalp to monitor the electrical activity of the brain in various conditions, including light stimulation generated by a strobe positioned in front of the eyes. An abnormal response when the patient is exposed to various frequencies of flashing lights indicates the presence of photosensitivity. If you have not been diagnosed with epilepsy or have not had this type of test and are concerned, ask your doctor about ordering one for you, or consult a local neurologist.
The same concerns may apply to relatives of individuals who are known to be photosensitive, such as siblings. Because the condition is genetic it may affect other members of the same family. Finding out if you are photosensitive or not is relevant, especially if the relatives are children or adolescents who intend to engage in activities presenting risks such as intense videogame playing.
If you are diagnosed with photosensitive epilepsy, your doctor may prescribe medication and suggest that you:
- avoid exposure to certain kinds of flashing lights; and
- cover one eye and turn away from the direct light source when in the presence of flashing lights.
You may also wish to discuss with your doctor whether the following tips suggested by photosensitivity and epilepsy experts would be helpful to you.
- Watch television in a well-lit room to reduce the contrast between light from the set and light in the room.
- Reduce the brightness of the screen.
- Keep as far back from the screen as possible.
- Use the remote control to change channels on the TV so you won’t have to get too close to the set.
- Avoid watching for long periods of time.
- Wear polarized sunglasses while viewing television to reduce glare.
- Use a flicker-free monitor (LCD display or flat screen).
- Use a monitor glare guard.
- Wear non-glare glasses to reduce glare from the screen.
- Take frequent breaks from tasks involving the computer.
- Sit at least 2 feet from the screen in a well-lit room.
- Reduce the brightness of the screen.
- Do not let children play videogames if they are tired.
- Take frequent breaks from the games and look away from the screen every once in a while. Do not close and open eyes while looking at the screen – blinking may facilitate seizures in sensitive individuals.
- Cover one eye while playing; alternating which eye is covered at regular intervals.
- Turn the game off if strange or unusual feelings or body jerks develop.
Exposure to Strong Environmental Lights
- Cover one eye (either one) with one hand until the stimulus is over. Closing both eyes or turning your eyes in another direction will not help.
Source: The Epilepsy Foundation