I have had photosensitive
epilepsy for the past 16 years and have faced many problems because
of it. I am mainly sensitive to the flicker of fluorescent lighting
and as these dominate most shops and buildings they are difficult to
avoid. My seizures are also provoked by flashing strobe light and looking
at certain visual patterns.
is photosensitive epilepsy?
sensitivity to flickering or intermittent light stimulation but includes
sensitivity to visual patterns. Photosensitivity therefore can be defined
as recurrent convulsions precipitated by visual stimuli. (Harding
& Jeavons, 1994) Approximately 1 in 200 of the population has epilepsy
and of these only a few per cent have photosensitive epilepsy. It is
often assumed that everybody with epilepsy is photosensitive whereas
in fact there are relatively few.
Factors that trigger seizures in photosensitive epilepsy
Both natural and artificial
sources of light may precipitate seizures but the most common trigger
seems to be television and the playing of certain computer games. Early
reports of epileptic seizures being provoked by watching television
were said to be because the sets were defective and therefore flickered,
or the vertical hold was faulty, causing the picture to roll. After
more clinical investigations it has been found that seizures can also
be provoked by a normally functioning television when the viewer is
too near the set. The factor that is most important here is that the
larger area of the retina of the eye which is stimulated by the flicker
frequency of the picture is, in fact, functioning normally. The nearer
the person is to the set, the more the picture is filling the whole
field of vision and so there is more likely to be an abnormal response
in the brain and therefore a seizure occurs.
off wet surfaces or through the leaves of trees, or seen when moving
rapidly past trees or railings illuminated by sunlight shining from
the side can provoke a seizure.
Flashing lights such
as those used in discos and also fluorescent lighting may induce seizures.
The amount of
photosensitive seizures has increased since the introduction of Visual
Display Units into the workplace and schools. Whereas the distance from
a television set can be placed at 8 feet or more, it is not always possible
to do so with a VDU because of the length of cable on a keyboard. The
risk of a seizure occurring depends on the material being displayed.
Most current computer displays have scan frequencies that are unlikely
to provoke seizures. Computer displays with liquid crystal screens are
flicker free. However there are still some computer games where a conventional
television monitor is used and these have the same drawbacks as television.
In general, the higher the frequency of the display screen, the better
it is for a person with photosensitive epilepsy.
are sensitive to various geometric shapes or patterns e.g. stripes or
checks Looking out of a window in a moving train can provoke a seizure
as can looking at a moving escalator.
How can I tell if Im photosensitive?
Most people are aware that
they are. An E.E.G. is done with photic stimulation (flashing light)
and photosensitivity is usual diagnosed at this stage.
1. Seek advice from your
doctor as the risk of seizures varies from person to person.
2. Covering or shutting one eye can reduce the effects of a flashing
or flickering light.
3. Television should always be watched in a well lit room from a distance
of 2.5 metres or more and it is helpful to place a small table lamp
on top of the set. You should avoid approaching the television to adjust
or switch channels. Again, you should cover one eye with the palm of
your hand if you do have to go near the set. This is where remote control
comes in handy. Sets with a higher frequency (100 hertz) or small screens
(less than 14) will also help.
4. Wearing polarised sunglasses outdoors in sunlight can reduce flickering
5. Avoid excessive tiredness as this may increase the risk of photosensitive
6. It is important to remember that reading from a computer screen for
a long time can make eyes feel tired and this could provoke a seizure
in some people. Regular breaks are advisable and anti glare screens
are recommended for eyestrain.
I myself follow all the above
guidelines and find them to be very helpful in the day to day living
with photosensitive epilepsy. However it is important not to put blanket
restrictions on all people with epilepsy, presuming that they are photosensitive.
Although for those who have photosensitive epilepsy life can be restricted,
it is still a relatively rare condition and unnecessary constraints
on peoples lifestyles should be avoided.
Graham Harding & Peter M.Jeavons