Okay, __X___ syndrome is an extremely rare occurrence which is symptomatic of brain damage. What happens is, the affected person can't see. But he doesn't tell anyone about it only because he doesn't believe that he can't. He behaves normally and it is only when he collides with his surroundings or trips or something to that effect do the people around him realise that something's wrong with his vision.
ailment
What is __X__?
