The character sees any objects or beings that are invisible, as well as any that are astral or ethereal, as if they were normally visible.
The spell does not reveal the method used to obtain invisibility, though an astral traveler is easy to identify if he has a silver cord. It does not reveal illusions or enable the character to see through opaque objects. It does not reveal creatures who are simply hiding, concealed, or otherwise hard to see.
So, does the spell actually tell you that someone is otherwise undetectable through normal vision, or do you truly see them "as if they were normally visible?"
Would it make a difference if one's ability to see invisibility were extraordinary, as it is for a pseudodragon?