Photosensitive epilepsy

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 (sich as strobe 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. 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 people with PSE. 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.

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 (PPR), 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.

No cure is available for PSE, although the sensitivity of some people 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.

PSE affects approximately one in 4,000 people, or 5% of individuals with epilepsy.[1] It is more common in women and people who are younger.[1]

Photosensitive epilepsy was again brought to public attention in December 1997 when the Pokémon episode "Dennō Senshi Porygon" ("Cyber Soldier Porygon") was broadcast in Japan, showing a sequence of flickering images that triggered seizures simultaneously in hundreds of susceptible viewers (although 12,000 children reported symptoms which may be attributable to mass hysteria).[15][16]

In March 1997, the 25th episode of an anime series called YAT Anshin! Uchū Ryokō caused a similar incident, when a reported four children were taken to hospitals by ambulances after viewing a scene with red and white flashing colours.[17]

In March 2008, the Anonymous group of hackers was claimed to be behind an attack on a forum for people with epilepsy.[18] The Anonymous hackers in turn blamed the Church of Scientology for the attacks, saying they were falsified to hurt Anonymous' image.[18] The attacks first consisted of GIF images flashing at high speeds that were hidden in discussion threads with innocuous-sounding titles. Later attacks redirected web browsers to a page with "a more complex image designed to trigger seizures in both photosensitive and pattern-sensitive epileptics."[19] The technology website Wired News considered it to be "possibly the first computer attack to inflict physical harm on the victims".[19]

An animated segment of a film promoting the 2012 Summer Olympics was blamed for triggering seizures in people with photosensitive epilepsy. The charity Epilepsy Action received telephone calls from people who had seizures after watching the film on television and online. In response, the London 2012 Olympic Committee removed the offending segment from its website.[20]

In December 2016, Newsweek journalist Kurt Eichenwald, who has epilepsy, reportedly had a seizure after an internet troll intentionally sent him a flashing GIF via Twitter.[21] Three months later, the user behind the GIF was arrested and charged with cyberstalking.[22]

The 2018 Pixar film Incredibles 2 contains scenes with flashing lights starting about an hour into the film, in which a villain called the Screenslaver hypnotizes other characters. After concerns over possible triggering of seizures due to this scene, theatres posted warnings for audiences with this condition.[23]

Cyberpunk 2077, a video game released in December 2020, contains a "braindance" sequence with red and white flashing lights which reportedly resembles the patterns produced by medical devices used to intentionally trigger seizures. Liana Ruppert, a journalist for Game Informer who has photosensitive epilepsy, experienced a grand mal seizure while reviewing the game days before its release.[24] After criticism from epilepsy advocacy groups that the game's disclaimers were insufficient, CD Projekt Red announced work on a fix[25] and later patched the effect to be less likely seizure-inducing.[26]

• Reflex seizure

• Bureau M, Hirsch E, Vigevano F (2004). "Epilepsy and videogames". Epilepsia. 45 Suppl 1: 24–6. doi:10.1111/j.0013-9580.2004.451003.x. PMID 14706041. S2CID 2044136..
• Harding, Graham F.A.; Jeavons, Peter M. (1994). Photosensitive Epilepsy. Clinics in Developmental Medicine (New ed.). London: Mac Keith Press. ISBN 978-1898683025. LCCN 2008531085.

• HardingFPA Broadcast Flash and Pattern Analyser
• Photosensitive+Epilepsy at the U.S. National Library of Medicine Medical Subject Headings (MeSH)