Photosensitive epilepsy is a form of epilepsy

Epilepsy

Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

 in which seizure

Seizure

An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...

s are triggered

Seizure trigger

A seizure trigger is a factor that can cause a seizure in a person who either has epilepsy or does not. There are many known causes of seizures, and in some patients, it is possible to determine what triggers seizures in general or has led to the onset of a particular seizure...

 by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns.
Persons with PSE experience epileptiform seizures upon exposure to certain visual stimuli. The exact nature of the stimulus or stimuli that triggers the seizures varies from one patient to another, as does the nature and severity of the resulting seizures (ranging from brief absence seizure

Absence seizure

Absence seizures are one of several kinds of seizures. These seizures are sometimes referred to as petit mal seizures ....

s to full tonic–clonic seizures).