Some people with PSE, especially children, may exhibit an uncontrollable fascination with television images that trigger seizures, to such an extent that it may be necessary to physically keep them away from television sets. Modern digital television sets that cannot be maladjusted in this way and which refresh the image on the screen at very high speed present less of a risk than older, analog television sets. For people with PSE, it is especially hazardous to view television in a dark room, at close range, or when the television is out of adjustment and is showing a rapidly flickering image (as when the horizontal hold is incorrectly adjusted on analog television sets). Television has traditionally been the most common source of seizures in PSE. Sensitivity is increased by alcohol consumption, sleep deprivation, illness, and other forms of stress. Some patients are more sensitive with their eyes closed others are more sensitive with their eyes open. Stimuli perceived with both eyes are usually much more likely to cause seizures than stimuli seen with one eye only (which is why covering one eye may allow patients to avoid seizures when presented with visual challenges). Stimuli that fill the entire visual field are more likely to cause seizures than those that appear in only a portion of the visual field. The exact spacing of a pattern in time or space is important and varies from one individual to another: a patient may readily experience seizures when exposed to lights that flash seven times per second, but may be unaffected by lights that flash twice per second or twenty times per second. Some patients are more affected by patterns of certain colours than by patterns of other colours. Contrasts in colour alone (without changes in luminance) are rarely triggers for PSE. The patterns are usually high in luminance contrast (bright flashes of light alternating with darkness, or white bars against a black background). Several characteristics are common in the trigger stimuli of many people with PSE. In some cases, the trigger must be both spatially and temporally cyclic, such as a certain moving pattern of bars. Static spatial patterns such as stripes and squares may trigger seizures as well, even if they do not move. Flashing lights or rapidly changing or alternating images (as in clubs, around emergency vehicles, near overhead fans, in action movies or television programs, etc.) are examples of patterns in time that can trigger seizures, and these are the most common triggers. The visual trigger for a seizure is generally cyclic, forming a regular pattern in time or space. Many PSE patients experience an " aura" or feel odd sensations before the seizure occurs, and this can serve as a warning to a patient to move away from the trigger stimulus.
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The exact nature of the stimulus or stimuli that triggers the seizures varies from one patient to another, as does the nature and severity of the resulting seizures (ranging from brief absence seizures to full tonic–clonic seizures).
People with PSE experience epileptiform seizures upon exposure to certain visual stimuli. PSE affects approximately one in 4,000 people (5% of those with epilepsy). Photosensitive epilepsy ( PSE) is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights bold, regular patterns or regular moving patterns. Medical condition Photosensitive epilepsyĮpilepsy warning label on a pinball machine with video components
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