Why is bartleby the one with weak eyesight?

While it is true that Bartleby says that he has limited by his eyesight, the reality is he is gradually withdrawing and continues to "prefer not to" regardless of what the task. The attorney tries to understand, but the walls which Bartleby faces and the walls he puts between himself and the people around him inhibit his ability to do his job as a copyist and disables him mentally and emotionally until he dies in prison.