That same article continues that many factors must combine to trigger the photosensitive reaction.
Certain visual patterns, especially stripes of contrasting colors. Natural light, such as sunlight, especially when shimmering off water, flickering through trees or through the slats of Venetian blinds. Intense strobe lights like visual fire alarms. #MAKE IMAGES BLINK ON AND OFF CONTINUOUSLY IN POWERPOINT FOR MAC TV#
Certain video games or TV broadcasts containing rapid flashes or alternating patterns of different colors. Television screens or computer monitors due to the flicker or rolling images. The Epilepsy Foundation's article, Photosensitivity and Seizures, provides a list of triggers that may cause seizures in photosensitive people here's an excerpt from that list: Other disorders, such as disorientation, nausea, vomiting, and more can also be so severe that the user is unable to function. Seizures can be fatal, but even the ones that are "only" debilitating can be of such severity, that they render the user incapacitated. The point is, seizures most definitely can be and are fatal, and developers and designers are incredibly important to making the web a safer place for those with sensitivities to photosensitive or musicogenic triggers. It is not frequent but it is a very real problem and people need to be aware of its risk". In its article, "A Revised Definition of Epilepsy" the Epilepsy Foundation notes that…" a seizure is an event and epilepsy is the disease involving recurrent unprovoked seizures." According to the Epilepsy Foundation's page " How Serious Are Seizures?", " Sudden unexpected death in epilepsy (SUDEP) is likely the most common disease-related cause of death in with epilepsy. For a great introduction on the topic of musicogenic seizures, visit Epilepsy Ontario's web page on Musicogenic Seizures. Only a few types of epilepsies are photosensitive though, and the vast majority of epilepsies are not." In addition to seizures brought about by photosensitivity, listening to certain pieces of music can also trigger what are called musicogenic seizures, although these types of seizures seem to be much more rare. Selim Benbadis of USF's Comprehensive Epilepsy Program notes, "The only thing that is really documented is flashing lights, which can trigger seizures in patients with photosensitive epilepsy. The trigger that is well established and strong is flashing/strobe lights. "A pattern with the potential for provoking seizures contains clearly discernible stripes, numbering more than five light-dark pairs of stripes in any orientation" In addition to stripes, checkered patterns have also been known to cause photosensitive seizures, according to Cedars-Sinai.Īlthough static images are possible as triggers, they are less consistent. " Static or moving patterns of discernable light and dark stripes have the same effect as flashing lights because of the alternation of dark and bright areas." The Epilepsy Foundation of America Working Group is able to "quantify" the problem a little. The fact that static images may cause seizures and other disorders is documented in such articles as “ Gamma Oscillations and photosensitive epilepsy”, where it is noted “ Certain visual images, even in the absence of motion or flicker, can trigger seizures in patients with photosensitive epilepsy” The Epilepsy Foundation, in its article, " Shedding Light on Photosensitivity, One of Epilepsy's Most Complex Conditions" talks about static images and patterns. Patterns and images can also trigger epilepsy. 
In the case of photosensitive epilepsy, seizures are triggered specifically by flashing lights, but other types of reflex epilepsies may be triggered by the act of reading, or by noises. Photosensitive epilepsy is actually a kind of "reflex epilepsy"-seizures occurring in response to a trigger. Certain visual patterns, especially stripes, can also cause physical reactions even though they are not animated. Web technologies that use video, animated gifs, animated pngs, animated SVGs, Canvas, and CSS or JavaScript animations are all capable of content that can induce seizures or other incapacitating physical reactions.
Content that flickers, flashes, or blinks can trigger photosensitive epilepsy.
Seizures caused by light are known as photosensitive epilepsy.
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