Hey Krzysiek_TATE,
To be able to do this you’ll have to, implement the IAISightTargetInterface on your character and override the virtual bool CanBeSeenFrom(const FVector& ObserverLocation, FVector& OutSeenLocation, int32& NumberOfLoSChecksPerformed, float& OutSightStrength, const AActor* IgnoreActor = NULL) function.
And in here you can make extra traces for vision.
Hope this is helpful to you 
Elias