I think it's possible to have mild epilepsy and pass the medical. The test (not sure if it's the same for pilot) is to sit you under a strobe with a load of wires sticking out of a cap attached to your head and the [inevidably attractive] nurse asks you to close your eyes. You lie there for 15 mins or so with the strobe flashing at various freqs, whilst the machine measures your brain activity.
The widely used (in ATC) Barco screens operate at about 70Hz, and the freq that can trigger epilepsy is about 7-10Hz.