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Important information . . .
People with PSE experience epileptiform seizures upon exposure to certain visual stimuli. 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). 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.
The visual trigger for a seizure is generally cyclic, forming a regular pattern in time or space. Flashing lights or rapidly changing or alternating images (as in clubs, around emergency vehicles, in action movies or television programs, etc.) are examples of patterns in time that can trigger seizures, and these are the most common triggers. Static spatial patterns such as stripes and squares may trigger seizures as well, even if they do not move. In some cases, the trigger must be both spatially and temporally cyclic, such as a certain moving pattern of bars.
Several characteristics are common in the trigger stimuli of many PSE patients. The patterns are usually high in luminance contrast (bright flashes of light alternating with darkness, or white bars against a black background). Contrasts in colour alone (without changes in luminance) are rarely triggers for PSE. Some patients are more affected by patterns of certain colours than by patterns of other colours. 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. 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. 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). Some patients are more sensitive with their eyes closed; others are more sensitive with their eyes open.
Sensitivity is increased by alcohol consumption, sleep deprivation, illness, and other forms of stress.
Television[edit]
Television has traditionally been the most common source of seizures in PSE. For patients 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). Modern digital television sets that cannot be maladjusted in this way and refresh the image on the screen at very high speed present less of a risk than older television sets.
Some PSE patients, 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. Some patients (particularly those with cognitive impairments, although most PSE patients have no such impairments) self-induce seizures by waving their fingers in front of their eyes in front of bright light or by other means.[1][2]
Some UK television broadcasters and studios now screen content through the "Harding FPA Test"[citation needed], an objective standard of assessment of potential to trigger seizures in the susceptible population.
Television programs[edit]
In some cases, specific television programs featuring certain types of visual stimuli have provoked seizures in a small minority of television viewers, including some viewers with no prior history of seizures of any kind. The "Dennō Senshi Porygon" episode of Pok?mon is the most frequently cited example (see the Public responsibilities section, below); broadcast of the program in Japan, which includes strong flickering scenes, produced seizures in a surprising number of viewers, even though the proportion of viewers affected was extremely low.[3]
Fluorescent lighting[edit]
When functioning correctly, mains-powered fluorescent lighting has a flicker rate sufficiently high (twice the mains frequency, typically 100 Hz or 120 Hz) to reduce the occurrence of problems. However, a faulty fluorescent lamp can flicker at a much lower rate and trigger seizures.[4] Newer high-efficiency compact fluorescent lamps (CFL) with electronic ballast circuits operate at much higher frequencies (10?20 kHz) not normally perceivable by the human eye, though defective lights can still cause problems.
The Job Accommodation Network [5] lists reduction or elimination of fluorescent lighting as an appropriate accommodation for many conditions including epilepsy. The Canadian Department of Labour states that the newer lights are problematic for fewer people.[citation needed]
Video games and Pinball machines[edit]
The first case of epileptiform seizures related to a video game was reported in 1981.[6] Since then, "many cases of seizures triggered by VGs were reported, not only in photosensitive, but also in nonphotosensitive children and adolescents with epilepsy.....Specific preventive measures concerning the physical characteristics of images included in commercially available VGs (flash rate, choice of colours, patterns, and contrast) can lead in the future to a clear decrease of this problem."[6] Risks can be reduced through measures such as keeping a safe distance away from the screen (at least 2 meters).[6]
While computer displays in general present very little risk of producing seizures in PSE patients (much less risk than that presented by television sets), video games with rapidly changing images or highly regular patterns can produce seizures, and video games have increased in importance as triggers as they have become more common. Some people with no prior history of PSE may first experience a seizure while playing a video game. Often the sensitivity is very specific, e.g., it may be a specific scene in a specific game that causes seizures, and not any other scenes. Despite this, there are questions on the dangers of this, and calls for testing all video games for causing PSE.[7] Laws requiring PSE warnings be displayed on packages and/or stores have been proposed [8] and legal firms are keeping an eye on developments.[9] The Star Wars Episode I pinball machine, which had video components, included an epilepsy warning label,[10] as did Attack From Mars. [11]
Web design[edit]
As with video games, rapidly changing images or highly regular patterns such as flashing banner ads or irregular fonts can trigger seizures in people with photosensitive epilepsy. Two sets of guidelines exist to help web designers produce content that is safe for people with photosensitive epilepsy:
- The World Wide Web Consortium - Web Content Accessibility Guidelines (WCAG) Version 2.0, produced in 2008, specifies that content should not flash more than 3 times in any 1 second period. However it does allow flashing above this rate if the flashing is below the "general and red flashing thresholds". (Basically, it is OK to flash more than 3 times in a 1 second period if the flashing is small enough or low contrast enough.) [12]
- In the United States, websites provided by federal agencies are governed by section 508 of the Rehabilitation Act. The Act says that pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and less than 55 Hz.[13] The 508 regulations are currently being updated and are expected to use the same criteria as WCAG 2.0 when finished.
- A free tool for evaluating Web Content for flashing called the Photosensitive Epilepsy Analysis Tool (PEAT) [14] is available from the Trace R&D Center at the University of Wisconsin-Madison.
The pain in so many asses.
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