Nobody knows, but what it does is remarkable
This study, and many similar to it, suggest that Hypnosis effects how the rods and cones structures of the eye operate. In other words making the eye see differently.
Hypnosis works for Weight loss, Stop Smoking, Alleviating stress, anxiety and phobias such as snakes, insects and elevators and flying, any one of which can be seriously debilitating.
A client the other day remarked that hypnosis felt to her like meditation, but without the hours of practice.