Photosensitive Epilepsy
(PSE) - What You Should Know

Photosensitivity is sensitivity to flickering or intermittent light stimulation and visual patterns. It affects approximately one in four thousand people. A number of people have this sensitivity but have not yet had a seizure and therefore have not been diagnosed with the condition of photosensitive epilepsy. The most common trigger for photosensitive epilepsy in Europe is the domestic television set. Almost fifty percent of patients are sensitive to the 50Hz flicker of television, and some seventy five percent of patients are sensitive to the 25 Hz flicker from the line raster which can be observed with close viewing. The onset of photosensitive epilepsy in an individual occurs typically around the time of puberty; in the age group 7 to 20 years the condition is five times as common as in the general population. Three quarters of patients remain photosensitive for life.
In response to a Pot Noodles advert in 1993 which induced photosensitive epileptic seizures in 3 people, the ITC introduced its Guidelines for Flashing Images and Regular Patterns. The sequences to be avoided sound relatively simple - repetitive bright or red flashes and spatial patterns - but the details are complicated.
In December 1997 a children's Pokemon cartoon episode in Japan produced 685 admissions to hospital. 560 cases were shown to have had proved seizures, triggered by four seconds of alternating saturated red and blue light used in the programme. Of those patients, 76 percent had no previous history of seizures. The Guidelines have since been updated.
Professor Graham Harding, an expert on Photosensitive Epilepsy who assisted with the drafting of the Guidelines, also collaborated in developing the Harding FPA.
Immediate Help For Photosensitive Epilepsy
From Ted Twietmeyer
Jeff -
The article on this affliction is interesting. It is true that television flickers at the frame rate. The screen phosphor storage time (the amount of time a phosphor dot on the screen stays on after the electron beam passes it) is measured in milliseconds. Hence, the entire screen will flicker as the author stated. I also know someone with photosensitive epilepsy. For him the flicker rate is different - he can look at televisiona and even works with computer monitors. However, sunlight passing through leafless branches of trees while in a moving vehicle will trigger an attack for him. He can never drive, and his wife must drive him everywhere.
But, there is help for those sensitive to television screens (although still not a cheap solution.) Newer LCD television screens create an image without using phosphor scanning. Hence, there is no 50Hz flicker. Although LCD panels flicker at the DC to AC inverter rate crated by the florescent backlight drive circuit, this frequency is up above 20KHz and therefore not an issue. The photoreceptors in the eye cannot respond that fast, and therefore do not send any pulsed neural signals to the brain to trigger epilepsy.
One way to test a CRT for flicker, is to use your peripheral vision. These photoreceptors respond much faster than pulsed light near the center of the eye. Look off to the side of any CRT screen at about a 45 degree angle, and see if any flicker is perceptable. Even a computer monitor running at 75Hz can be faintly observed to flicker using this test. An LCD panel will not flicker, because of a much higher time constant for each pixel.
Ted Twietmeyer

Ellen J. Botelho, OT
This was a great, informative article, but it sadly missed a big problem we epileptics face everyday: strobe lights. They are now on emergency vehicles, school busses, and in some public buildings fire alarm systems. My seizures are gone now, but I still have an almost instinctive feeling of dread whenever I drive behind a school bus or police car. I can't help but think: what if I weren't so lucky? What if every time I saw a strobe light, it triggered a seizure? Why didn't someone stop this trend, before they were all over our society?
So much for the Americans With Disabilities Act. The use of strobe lights all over our society is harmful to the health of epileptics, and no one seems to care. Many of us are imprisoned in our homes, because venturing out into society can be harmful to us.



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