Fading Vision within one eye?

My brother, who is 25, told me last darkness that he is losing vision within one eye. He has notice this in the ultimate 3 weeks.
He has be to an optometrist with no answer. He have been to an opthalmagist (sp?) near no answer, now he is going to another eye specialist (I don't know what benign, is there any other after an opthalmagist?). He have been advise that it may be something behind the eye, as at hand is nothing wrong beside his lens (ie no blurriness like near a catarct). He is going to get and 'eye mapping' done subsequent week. To me this whole point sounds terrible, close to it could be something to do with his brain.. Any suggestion recommended.. He is a reasonably in shape non smoker, not overweight either. I'm slightly worried.Fading Vision within one eye?
i wud suggest him to turn for a cat scan or a MRI i ad a brain hemorrhage when i be 11 so i know how important it is i hope everything go well
accurate luck
thats so weird because 2 years ago i get a numbness in my eyes and it hasnt gone away could be shabby nerves i dont know though
Anything to do with loss of verbs is worrysome.
He should ask for an M.R.I. to make sure that his brain is problem free.GOOD LUCK!!! lol.