Photosensitive epilepsy (PSE) is a form of epilepsy in which seizure are Seizure trigger by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns.

Symptoms

Persons 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 seizure to full tonic–clonic seizure . 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 an example 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 color alone (without changes in luminance) are rarely triggers for PSE. Some patients are more affected by patterns of certain colors than by patterns of other colors. 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

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. Some UK television broadcasters and studios now screen content through the "Harding Test , an objective standard of assessment of potential to trigger seizures in the susceptible population.

Television programs

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 [[Pokémon]]is the most frequently cited example (see the [[#Public responsibilities|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.lt;/ref>

2012 London Olympics promotional film incident

An animated segment of a film promoting the 2012 London Olympics was blamed for triggering seizures in people with photosensitive epilepsy. The charity Epilepsy Action received telephone calls from people who had had seizures after watching the film on television and online. In response, it was reported that London 2012 Olympic Committee removed the offending segment from its website.lt;/ref>

Fluorescent lighting

When functioning correctly, the flicker rate of fluorescent lighting is very high (twice the mains frequency). However, a faulty fluorescent lamp can flicker at a much lower rate and trigger seizures.British Epilepsy Association The Job Accommodation Network http://www.jan.wvu.edu Job Accommodation Network] lists reduction or elimination of fluorescent lighting as an appropriate accommodation for many conditions including epilepsy. The Canadian Department of Labor states that the newer lights are problematic for fewer people.

Video games

The first case of epileptiform seizures related to a video game was reported in 1981.Bureau M, Hirsch E, Vigevano F (2004). "Epilepsy and videogames". Epilepsia 45 Suppl 1: 24–26. PMID 14706041. 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 colors, patterns, and contrast) can lead in the future to a clear decrease of this problem." Risks can be reduced through measures such as keeping a safe distance away from the screen (at least 2 meters). 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. Most video games are required by lawto include a warning for PSE sufferers describing the increased risk of seizures that gamers may experience.

Web design

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 have produced Web Content Accessibility Guidelines Version 2, produced in 2008, suggest designers allow users to control flickering or avoid causing the screen to flicker at all.http://www.w3.org/TR/WAI-WEBCONTENT/#gl-movement *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 Hertz and less than 55 Hz.http://www.section508.gov/index.cfm?FuseActionContent&ID12#Web

Diagnosis

Diagnosis may be made by noting the correlation between exposure to specific visual stimuli and seizure activity. More precise investigation can be carried out by combining an EEG with a device producing [[Intermittent Photic Stimulation]](IPS). The IPS device produces specific types of stimuli that can be controlled and adjusted with precision. The testing physician adjusts the IPS device and looks for characteristic anomalies in the EEG, such as [[photoparoxysmal response]](photoparoxysmal response , that are consistent with PSE and/or may herald the onset of seizure activity. The testing is halted before a seizure actually occurs. Sometimes diagnostic indicators consistent with PSE can be found through provocative testing with IPS, and yet no seizures may ever occur in real-life situations. Many people will show PSE-like abnormalities in brain activity with sufficiently aggressive stimulation, but they never experience seizures and are not considered to have PSE.

Treatment and prognosis

No cure is available for PSE, although the sensitivity of some patients may diminish over time. Medical treatment is available to reduce sensitivity, with sodium valproate being commonly prescribed. Patients can also learn to avoid situations in which they might be exposed to stimuli that trigger seizures and/or take steps to diminish their sensitivity (as by covering one eye) if they are unavoidably exposed. These actions together can reduce the risk of seizures to almost zero for many PSE patients. Some PSE patients have trigger stimuli that are so specific that they are never likely to encounter them in real life. Their PSE may only be discovered by accident in an unusual situation or during examination for other complaints.

Public responsibilities

Image:Pikachu seizure-2.jpg The effects of strobe light became apparent when it first became popular in discotheque during the 1960s. Many authorities responded by regulating the permissible frequency ranges of flashing lights in public places. Photosensitive epilepsy was again brought to public attention in late 1997 when the [[Pokémon (anime)|Pokémon]]episode "Dennō Senshi Porygon (aka "Electric Soldier Porygon") was broadcast in Japan, showing a sequence of flickering images that triggered seizures simultaneously in hundreds of susceptible viewers (although mass hysteria caused 12,000 children to report seizure-like syndromes).lt;/ref> In March 1997, the 25th episode of an anime series called [[YAT Anshin! Uchū Ryokō]]had a similar incident when a reported four children were taken to hospitals by ambulances when a scene with red and white colors flashed. In March 2008, the Anonymous (group) group of hackers was claimed to be behind an attack on a forum for epilepsy sufferers.http://www.news.com.au/technology/story/0,25642,23460969-5014239,00.html Anonymous attack targets epilepsy victims] The hackers, part of Anonymous_(group) blamed the Church of Scientology for the attacks saying they were made to hurt their image. The attack consisted of Graphics Interchange Format images flashing at high speeds that were hidden in threads with innocuous-sounding titles. The technology website Wired News considers it to be the first physical attack on Internet users.http://www.wired.com/politics/security/news/2008/03/epilepsy Wired Hackers assault epilepsy patients via computer]

Bucha effect / Flicker vertigo

A related condition is the Bucha effect or Flicker vertigo Without going as far as epilepsy, after exposure to stroboscopic light the victims feel dizzy, disorientated and debilitated. It was discovered after a series of helicopter crashes caused by the pilot being incapacitated by the stroboscopic light generated by the rotor blades.

See also

* Epilepsy * Seizure * Seizure trigger * Breakthrough seizure * Henri Gastaut neurologist * Strobe light * Bucha effect * Psychogenic non-epileptic seizures * Dreamachine * Video Games * Dennō Senshi Porygon

References

Bureau M, Hirsch E, Vigevano F (2004). "Epilepsy and videogames". Epilepsia 45 Suppl 1: 24–6. PMID 14706041.

Further reading

* Harding, Graham et al.(1994). Photosensitive Epilepsy.Mac Keith Press, London.

External links

* http://www.epilepsyfoundation.org/about/photosensitivity/ Photosensitivity information] from Epilepsy Foundation * http://www.epilepsy.org.uk/info/photo.html Photosensitive epilepsy information] from Epilepsy Action * http://www.epilepsynse.org.uk/pages/info/leaflets/photo.cfm Information on photosensitive epilepsy] from The National Society for Epilepsy * http://www.hardingfpa.tv HardingFPA Broadcast Flash and Pattern Analyser] * * http://www.emedicine.com/neuro/fulltopic/topic687.htm#section~Introduction Reflex Epilepsyby Hulihan, Joseph F] Category:Epilepsy types el:Φωτοεπιληψία es:Epilepsia fotosensitiva ko:광과민성 발작 ja:光過敏性発作