Photosensitivity is an abnormal clinical or electroencephalographic (EEG) response to light. Photosensitive seizures are provoked by light stimuli. Seizures triggered by specific stimuli are called reflex seizures.

Television and electronic games are major factors that evoke seizures. Other light sources include flickering or reflected sunlight, lightning, car headlights, flickering artificial lights, arcade games, discotheque or Christmas lights, sharply contrasting patterns, and, rarely, self-induced exposure to flicking light e.g., waving a hand before the eyes.

Seizures may occur only in response to light stimulation (pure photosensitive epilepsy) or they may occur spontaneously but may be triggered by light stimulation (epilepsies or epileptic syndromes in which photosensitive seizures may occur).

Most people (84%) with photosensitive epilepsy have generalized tonic-clonic seizures in response to light. Absence seizures with or without eyelid movements, lip smacking or mouthing occurred in 6%. Bilateral myoclonic seizures occurred in 1.5%; focal seizures, in 2.5%, and mixed, in 6%.

Recent clinical and EEG data suggest that at least 17% of people with photosensitive seizures may have focal occipital lobe (visual cortex) seizures with secondary generalization. Subtypes include idiopathic photosensitive occipital lobe epilepsy and other visual sensitive epilepsies.

Most people with photosensitive seizures are between 5 and 19 years of age. This tendency greatly decreases after 25 years of age.Women are more likely to experience photosensitive seizures than men (62% vs. 38%) at all ages. However, men are more likely to suffer video game-induced seizures.

Photosensitive seizures occur in some people with juvenile myoclonic epilepsy and childhood absence epilepsy. They may also occur in people with progressive myoclonus/ myoclonic epilepsies and symptomatic focal epilepsies, especially when the occipital lobe is involved.

EEG studies suggest that about 90% of people with prolonged photoconvulsive responses to light stimuli will have epileptic seizures. On EEG, these responses include generalized discharges, with spike and wave activity at 3 Hz, polyspikes, and irregular spike and wave discharges, which are not time-locked to the stimulus. This response is probably inherited on an autosomal dominant basis with agedependent penetrance. The maximum age of occurrence is 5 to 15 years.

In December 1997, about 700 Japanese children had seizures while watching an animated cartoon (Pokemon). About 1 in 4,923 children from 6 to 18 years of age had a seizure during the television episode. Most seizures occurred during a scene in which red and blue frames alternated at 12 Hz for 4 seconds.

Television is the most common stimulus for photosensitive seizures, whether watched for regular viewing, videos or electronic games. The basic frequency of the monitor causes flicker or changes in luminance. In Europe, this flicker is at 50 Hz; elsewhere, 60 Hz. At 50 Hz, 49% of people have a photoconvulsive response on EEG. Only 15% respond at 60 Hz. This difference explains the low incidence of TV-induced seizures in North America.

Factors that contribute to TV-induced seizures include: flickering light (especially at the frequency of the electrical supply), flashes or images; high contrast between images, e.g., alternating bright and dark frames; speed of change (lower the speed, the lower the risk, e.g., less than 3 per sec); rapid color changes, e.g., red is a provocative color; faulty vertical or horizontal holds; approaching to adjust the TV set; and sitting too close (60 cm or less). A 100-Hz screen is less provocative than a 50-Hz screen but more expensive.

Video-game epilepsy represents another form of photosensitive epilepsy. Some games are more likely to evoke seizures than others. Several factors explain why seizures occur during video games: photosensitive response to physical characteristics of the TV display, e.g., flicker at or near the frequency of the electrical supply; photosensitive response to the game’s visual content; specific cognitive activities, decision making, hand movements, etc; nonspecific emotional factors, such as anxiety or excitement; seizure threshold lowered by sleep deprivation or fatigue; and chance.

Ideally, the viewing distance should be at least four times the diagonal screen measurement, e.g., at least 3 m. The room should be well lit. Prolonged play (>1 hr per session) should be avoided. Children should not play when sleep deprived or febrile.

People with epilepsy or a family history of photosensitivity should not play electronic games until an EEG examination, including a period of patterned photic stimulation, has been done.

Photosensitive children should not play electronic games while they are alone, and they should not approach the television to adjust the set.

From a technical viewpoint, 100-Hz screens, games of <50 lux, and the use of special optical filters may minimize the risk of photosensitive seizures.

Children who have unprovoked and photosensitive seizures should be treated with an anticonvulsant, as should those who have frequent photosensitive seizures because they fail to comply with preventative measures. Most studies suggest valproic acid, but benzodiazepines, ethosuximide, lamotrigine and levetiracetam are also effective.

Photosensitive people should wear polarized glasses while in the sun. When exposed to outdoor sources of flickering light, the photosensitive person should cover one eye.