3D television (TV) and cinema have experienced a recent surge in popularity aided in part by the success of films such as “Toy Story 3” and “Avatar”. In parallel with this trend there have been increasing concerns about the safety of 3D TV and cinema for patients with photosensitive epilepsy. General practitioners, paediatricians and neurologists are being consulted about their opinions on the risk of triggering a seizure.
Photosensitive epilepsy occurs in 1 in 4000 of the population but the incidence is higher in people aged 7–19 years. We found little evidence in the literature and confusing advice on various websites. We discuss this evidence in an attempt to clarify the advice that health professionals should be giving on this issue.
We conclude that 3D cinema and television are only unlikely to trigger seizures in patients with non-photosensitive epilepsy. In young people with photosensitive epilepsy the risk of triggering a seizure is not greater with 3D TV or cinema than with conventional television, and we suggest means by which this risk can be minimised. We suggest removing 3D glasses when watching conventional TV to prevent the eyes from picking up flicker. Unfortunately there is currently insufficient evidence to draw more formal conclusions and clinical trials would be of great benefit.
The estimated prevalence of photosensitive epilepsy is about 1 in 4000 among the population with an incidence of 1.1 per 100,000. In children and adolescents between 7 and 19 years of age the incidence of photosensitive epilepsy is estimated at 5.7 per 100,000.
- Harding G.F.A.
- Jeavons P.M.
The peak age of onset is around puberty and girls are more likely to be affected than boys by a ratio of 2:1. In the majority of patients, photosensitive epilepsy persists throughout the adult life, but 25% of patients lose photosensitivity by the age of 40 years.
- Harding G.F.A.
- Jeavons P.M.
Generalised tonic–clonic seizures are the most common type of epilepsy in photosensitive patients, but other types of seizure may also occur.
Television programmes containing flashing or repetitive patterns are the most common trigger factors for photosensitive epilepsy. In the UK, since 1994 TV broadcast guidelines have restricted such material to a large extent and a warning to viewers is issued at the start of any such programme that contains provocative images. These measures have reassured patients as seen by the reduction in the number of complaints both to UK epilepsy societies and Ofcom (the independent regulator and competition authority for the UK communications industries). Seizures usually occur either immediately or shortly after presentation with a precipitating stimulus.
Over the past 10 years patients have expressed concerns to doctors, nurses and patient support groups about the safety of 3D movies and TV programmes especially after the highly popular films such as Toy Story 3 and Avatar became widely available. Unfortunately a good advice to patients and their families is hard to find in the current medical literature. Therefore, we examined the available evidence in order to clarify the risk of 3D TV and cinema in triggering seizures in patients with photosensitive epilepsy.
2. Risk assessment of 3D films on photosensitive epilepsy
The mechanism in which TV and cinema movies trigger seizures in patients with photosensitive epilepsy is related to several factors including the light intensity, the environment and the frequency of picture frames per second. Normal 2D movies have a frame rate of 24 per second, which may pose a risk for patients with photosensitive epilepsy, but the light intensity in the cinema is very low and there are relatively a few reports of seizures precipitated in cinemas. In contrast, 3D movies project images at 48 frames per second aimed, by the use of coloured or polarising filters, at different eyes and resulting in 24 frames per second per eye. The polarising effect of 3D films may reduce the light output by around fifty percent leading to a reduced risk to trigger a seizure to people with photosensitive epilepsy. Therefore, the risk of 3D movies to trigger a seizure is around fifty percent less than with conventional 2D movies. However if provocative material such as flashing light is presented the risk can be as high as that for normal 2D movies.
Based on the understanding of these mechanisms and from advice form one of the authors (GH), the National Society for Epilepsy (NSE) advises that “because of the size of the screen and the low intensity it is rare for seizures to be triggered while watching 3D films”. Epilepsy Action states that “cinema films, including 3D, do not pose a risk for people with photosensitive epilepsy. However, some films contain images, such as flashing lights that could trigger a seizure”.
In Britain, the Health and Safety Executive (HSE) requires cinemas and TV broadcasters to display warnings regarding flashing lights and the risk of seizures in people with epilepsy. The HSE also recommends that the flashing lights are restricted to less than 5 flashes per second. In practice the warning is not always displayed clearly and hence the risk may always be present.
Reporting on patients and parents experience with 3D movies on epilepsy websites can provide valuable insight into the effects of 3D movies on patients with photosensitive epilepsy. Unfortunately, the reliability of these reports cannot always be assessed with confidence as some parents reported seizures in patients who are not known to have photosensitive epilepsy. On one blog, a father described his son who suffers from Benign Rolandic Epilepsy to have seizures on 2 occasions after watching a 3D movie. Another parent on the same blog described how her teenage son, who had no previous history of epilepsy, reported a “weird” feeling during a 3D movie followed by what sounded like a generalised seizure.
The association of these events with 3D movies can be extremely difficult to interpret. In particular, it is not possible to establish a cause and effect relationship as other trigger factors cannot be excluded. However such reports do cause a great deal of anxiety and fear among the patients and the parents of children with epilepsy.
Public anxiety was also heightened by a major manufacturer of TV sets issuing a warning about the possible increased risk of stroke and epilepsy to some viewers. The product warning states: “Some viewers may experience an epileptic seizure or stroke when exposed to certain flashing images or lights contained in certain television pictures or video games. If you or any of your family has a history of epilepsy or stroke, please consult with a medical specialist before using the 3D function.” The warning states that “the risk is greater to children and teenagers” and hence advises parents to monitor them closely, recommending frequent breaks to reduce these effects.
Another major TV manufacturer demonstrated the variation in light flickers due to normal and 3D TV movies. The technique involves the use of shutter glasses. The image is presented at either 100 or 120 Hz and the synchronised shutter glasses present the image to each eye at 50 or 60 Hz. It was shown that 3D movies were associated with no apparent light flicker, but on switching to normal TV films while still wearing the 3D shutter glasses there was severe flicker of light for about 3 s until the shutter glasses recognised the absence of the 3D presentation. In addition any normal monitor viewed at the same time showed severe and continuous flicker. It is, therefore, essential that patients and parents are aware of this phenomenon while wearing 3D glasses and watching normal 2D films.
Recent screen technology seems to provide some protective qualities against light flicker. Liquid crystal display (LCD) and plasma screen televisions do not use the scanning lines and therefore are less likely to trigger seizures than the conventional cathode ray tube (CRT) televisions. Plasma screens tend to be brighter and have higher contrast than LCD televisions; this increased contrast may increase the risk of seizure activation. For patients with photosensitive epilepsy, the current advice is to opt for a LCD television over a plasma or CRT.
Patients may also appreciate the safety advice given by the Epilepsy Action website shown in Box 1
Box 1 Safety suggestions when watching television .
Watch the television in a well-lit room.
Have a lamp lit close to the television.
Watch the television from a distance of at least 2.5 m (eight feet).
Use the remote control wherever possible – from a safe distance – to adjust the television or to change channels.
If you have to go near the television, cover one of your eyes with the palm of your hand. This will cut down the number of brain cells that are stimulated by any flicker on the screen.
The current evidence is limited and future research is needed for more robust conclusions to be made. However, it is reasonable to conclude:
For patients with non-photosensitive epilepsy the risk of 3D movies triggering a seizure is negligible.
In patients with photosensitive epilepsy, the risks of a seizure being triggered by 3D movies is not greater than conventional 2D programmes.
LCD TV screens are less likely to trigger a seizure than plasma and CRT TV screens.
The risk of photosensitivity can be minimised further by following the general advice outlined above.
Epilepsy Action also advise to remove 3D glasses when changing from a 3D programme to conventional television to prevent the eye lenses from picking up flickering, which can trigger a seizure.
Photosensitive epilepsy occurs in approximately 1 in 4000 of the population.
The most common precipitant for photosensitive seizure is material containing flashing or repetitive patterns.
In a child with photosensitive epilepsy, the risk of 3D cinema triggering seizure is fifty percent less than with conventional films.
In a child with photosensitive epilepsy, the risks of a seizure being triggered by 3D television is not greater than conventional television.
Conflict of interest
Published online: September 21, 2011
Received in revised form:
© 2011 British Epilepsy Association. Published by Elsevier Inc.