Just something I did really quick to show how Zolterdeus sees.

The top is how a normal person sees, while the bottom is how he sees.

The Shadow eye (left) is very sensitive to light, so it hurts to use it. Unless it's nearly pitch dark out, it's basically useless, so that's why he has to wear the eye patch over it.

His other eye used to be normal, then the accident/attack (I still dunno what excuse I'm gonna give) fucked up his eye like that. So now he can only see clearly in a limited view (the middle of the cross is where he's currently looking), while his peripherals are coated in red now.