Photosensitive epilepsies

In visual sensitive (or photosensitive) epilepsies, seizures are precipitated by environmental photic stimuli. The age of onset peaks at 11 years. The term photosensitivity only designates the abnormal EEG response to flickering light, a finding also observed in 4% of healthy children or adolescents. Photic-induced absences, myoclonic seizures, and general tonic-clonic seizures are observed in idiopathic generalised epilepsies and in Dravet’s syndrome. Single or repeated seizures when playing video games or in front of the television (especially with a 50 Hz screen) might appear without a history of spontaneous seizures.  The seizures manifest as either general tonic-clonic seizures or prolonged attacks with visual symptoms and vomiting. An outbreak was reported in Japan, where several hundreds of children and adolescents experienced a seizure when watching  a popular cartoon. Self-induction is sometimes observed, especially in children with absences or myoclonic jerks who indulge in compulsively staring or blinking in front of light sources or contrasted patterns. 
Sensitivity to visual stimuli is associated with the inability of the visual cortex to process afferent inputs of high luminance and contrast through the normal mechanisms of cortical gain control. 
If attacks are infrequent, preventive measures might be sufficient. The triggering power of 50 Hz television screens is lowered by strengthing  the ambient light and by watching at a distance >2,5 m. 100 Hz television screens are much less provocative. Video games should be avoided. If treatment is necessary, valproate is the drug of choice. Polarised glasses or optical filters for screens have proved helpful in severe cases.

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