Hoffman's virtual worlds, which he calls by names such as SnowWorld or SpiderWorld, are designed to immerse the user so deeply in the virtual experience that their attention is distracted away from the pain.

SnowWorld, for instance, takes users on an absorbing virtual journey through glaciers and ice caves whilst having to defend themselves from attack by polar bears and penguins.

Mike Robinson, a patient who has undergone the virtual reality treatment, said it helped him to overcome the extreme discomfort he felt when his dressings were changed.

"My pain when the nurse is changing my bandages is consistently extreme," he told BBC News Online. "But during the time I was in VR, I was pretty much unaware that the nurse was even working on my wound. "I mean, at some level I knew she was working on me, but I wasn't thinking about it because I was inside that SnowWorld."

"Pain requires conscious attention. Humans have a limited amount of this and it's hard to do two things at once,"