Resources > Photosensitive Epilepsy (PSE)
Photosensitive epilepsy is the name given to the type of epilepsy in which seizures are provoked by flashing or flickering light, or, in some cases, visual patterns. It affects more than one in four thousand people.
As well as those who are known to have the condition, many more people may have this sensitivity but have not yet had a seizure and therefore have not been diagnosed.
The onset of photosensitive epilepsy in an individual typically occurs 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. At this age seizures are terrifying for the individual, deeply distressing for families and friends and profoundly life changing for all concerned. As well as emotional distress, seizures also carry inherent and situational risks which often include physical harm and can and have lead to loss of life. Once triggered, three quarters of patients remain photosensitive for life.
Both natural and artificially occuring light may trigger seizures, but one of the most common triggers for photosensitive epilepsy is the domestic television set. The television set doesn’t cause the photosensitive epilepsy, but watching it can and does trigger seizures in people where the condition is present even though it may be dormant. Other triggers include stroboscopic lighting, illuminated patterns and other forms of video such as games, digital signage, digital cinema, computer displays and web content.
There are three main stimuli that can trigger photosensitive seizures, bright flashing where there is a rapid change in luminance, colour changes to and from a saturated red, and certain spatial patterns consisting of regular light and dark features. Photosensitive individuals may be sensitive to different levels of stimulation and to all or just some of the stimuli.
In the UK, in response to a Pot Noodles advert in 1993 which was irrefutably found to have caused a number of photosensitive epileptic seizures, the Independent Television Commission (ITC) introduced its 'Guidelines for Flashing Images and Regular Patterns'.
In December 1997 a children's Pokemon cartoon episode in Japan produced 685 admissions to hospital. 560 cases were shown to have had proven seizures, triggered by a four second sequence of alternating saturated red and blue light used in the programme. Of those patients, 76 percent had no previous history of seizures. This led to the adoption of 'Guidelines for Flashing Images and Regular Patterns in Television' in Japan.
In December 2003, the UK Government's Office of Communications (OfCOM) inherited the duties of the ITC in the UK. They published a 'Guidance Note for Licensees on Flashing Images and Regular Patterns in Television' as part of the licensing conditions for UK broadcasters.
Even with these guidelines in place events can still happen. In 2008 the broadcast of a promotional video launching the new logo for the London 2012 Olympics as part of an early morning news program led to 30 reported seizures. Unfortunately this material had not been checked for compliance to the UK Guidelines prior to broadcast. When it was checked on a HardingFPA system, significant levels of non-compliant flashing were found.
With the march of technology, new sources of imagery, and continual market demands for exciting new visual styles and high impact effects, there is an increasing risk to the public of experiencing a photosensitive epileptic seizure. In response to this and following reports of seizures triggered by hand held video games, in 2008 John Penrose a member of the UK parliament started a campaign to extend the UK’s OfCOM Guidelines to cover other sources of video imagery including Video Games, DVD’s, digital signage and web based content. Discussions are ongoing.
Note: Professor Graham Harding, an acknowledged expert on Photosensitive Epilepsy who assisted in the drafting of the UK, ITU and Japanese Guidelines, also collaborated in developing the HardingFPA system and acts as a scientific advisor for Cambridge Research Systems Ltd.