An Investigation into the performance of a Virtual Mirror Box for the treatment of Phantom Limb Pain in Amputees using Augmented Reality Technology

Augmented Reality (AR) and the environments that it creates have the ability to change a person’s sensory experience in various ways. The therapeutic potential of AR has only recently been realised and more applications of this technology are gradually being utilised for the treatment of people suffering from phobias, severe burns and spinal cord lesions. Augmented environments can be used to distract the attention of patients from excruciatingly painful or terrifying experiences. Phantom limb pain occurs when a person feels pain that he/she attributes to the area of a limb that has been removed. Phantom limb pain can be very severe and disabling. It continues to be experienced by two thirds of amputees, eight years post-amputation. V.S. Ramachandran developed a technique to treat phantom limb pain in upper limb amputees by using an ordinary mirror. The patients placed their intact arm into a box, which contained a mirror down the mid-line, so that when viewed from slightly off-centre, the reflection of their arm gave the impression that the patient had two intact arms. When the patients moved their intact arms, their phantoms appeared to move in synchrony. Whilst this method had positive therapeutic value for some patients, it was completely ineffective for others. Individual differences were observed in the extent to which patients were susceptible to the illusion that the reflected arm was in fact their own. This led to great variability in the experienced authenticity of the mirror box illusion. Each amputee has his/her own individual perception of the phantom limb. The phantom limb may be shorter, or longer, have some parts thicker or thinner, be continuous, or have gaps in it, in comparison to the original limb. This would appear to be why the mirror box is so successful for some, yet completely ineffective for others. We have developed, using a data glove and Augmented Reality, an environment in which upper limb amputees can have their phantom limbs individually tailored to represent their own perception of their missing limb. They can then experience a virtual mirror box by wearing a data glove and a magnetic sensory device on their intact limb, whilst watching their phantom move in unison on a flat screen positioned where the mirror should be. This can also be set up to allow for motion of the phantom in the same direction as that of the intact limb, something that cannot be experienced with the mirror.