From reviewer Emanuel Levy:
Henry's quest to be saved brings him into contact with a blind
psychiatrist, Dr. Leon Patterson (Bob Hoskins), who is either Sam's
mentor or Henry's deceased father–depending on your perception. The
scene in which Leon regains his sight with Henry's help is played as a
metaphor and reality, tapping into the roots of father-son
relationships, suggesting the ways children wish their parent can see
them for whom they really are. Like every element in the film, Leon's
blindness is part of a symbolic structure but also part of reality.
If you take this as a film about how the mind deals with its dying moments, and the way it might attempt to make sense of what is happening in the way our dreams do, melding in the current reality (people and comments from the accident scene), then every character in the story becomes a symbolic version of the self. So maybe the fatherly, perhaps judgmental side of himself was blind, then begins to see.
Director Marc Forster has admitted, though, in interviews that the movie has plot holes:
Speaking objectively, narratively speaking, there are definitely
things that do not work in Stay, and don’t tie together. That was
more for me; it was like a painting and going through an experience of
images. Narratively speaking, it definitely has holes. If you look at
the film rationally you can point at the holes and say, “This and that
are ridiculous.” For me, I didn’t really care if anyone didn’t like
the movie, because I really like the movie.
Alongside another interview, done at the time of the release, there is a photo of the blind psychiatrist/father with a caption: I’m confused!
So many Hollywood movies are explained from start to finish. I think
it's important to ask questions and to be left in the unknown, because
I think you get more out of it... Stay should be taken as a visual
The actors and I tried to discuss [what was going on] in the
beginning, but we soon noticed that everybody needs to come up with
his own logic. As a director I then had to direct them intuitively.
Someone might think now that if a movie is not set in the real world,
you can do whatever you want. But it's not like this. It's much more
difficult. It was one of the most difficult films to shoot for me in
that sense. But like this you start feeling a little like Ewan
McGregor's character, who tries to analyze the situation rationally
but the situation then gets more and more out of hand. Bob Hoskins
told me that he didn't understand the story even after reading the
script twice or three times. When I asked him why he still wanted to
make the movie with me, he said, that's exactly want interests him: to
find the character while making the film.
So no definitive answer, but some clues...