Visual Illusion

Visual illusion therapy is a cognitive technique which uses guided images to alter perceptions and modify behaviour. It has been used in various studies to alleviate pain responses by changing feelings of perceived discomfort (Kazdin 2001; Korn 2002; Kwekkeboom 2001). It is based on a cortical model of pathological pain (Harris, 1999). This model states that the injury causes a mismatch between motor output and sensory feedback which in turn contributes to the pain. Studies have found normalization of the cortical proprioception representation results in recovery from pain (Floor et al. 2000; Maihofner et al. 2004; Pleger et al. 2005).

Discussion

Two studies examined the effect of visual illusion in combination with transcranial direct current stimulation (tDCS; Soler et al. 2010; Kumru et al. 2012). Soler et al. (2010) examined the effectiveness of visual imagery for neuropathic pain post SCI. The authors found the greatest improvement in pain perception, pain reduction, ability to work, perform daily tasks, enjoyment, interference of sleep in the combined tDCS and visual illusion group (p<0.05). Thirty percent of participants in this combined group also reported a 30% or more improvement in pain intensity. The visual illusion group reported significant improvement in neuropathic pain intensity on the last day of treatment (p=0.02); however, the effect was not maintained over 12 weeks. One cohort study (Kumru et al. 2012) found that combined transcranial direct current stimulation and visual imagery may improve pain intensity among individuals with neuropathic pain post SCI.

Two studies examined virtual walking in improving neuropathic pain post SCI (Moseley et al. 2007; Jordan et al. 2016). Moseley (2007) reported on five individuals with both a T12-L3 paraplegia (AIS B) and neuropathic pain who engaged in a virtual activity, where they were led through a guided walking exercise, visualizing that they were walking pain free. Of the four subjects who completed the trial (one patient withdrew from the study earlier due to distress), there was a mean 42 mm reduction in neuropathic pain following individual treatments, and 53 and 42 mm reductions immediately and three months following virtual walking daily for three weeks based on a 100 mm visual analog scale. Control treatments were visual imagery alone, and watching a movie, both of which resulted in less dramatic pain reduction; however, no statistical comparisons were done. Jordan et al. (2016) compared virtual walking with virtual wheeling. The study found that those in the virtual walking group had a significant decrease in their neuropathic pain symptoms.

Viliger et al. (2013) provided virtual reality training in which participants were asked to complete four lower limb movement tasks. The study found significant decrease in pain intensity post treatment. Gustin et al. (2008) involved the participants to imagine right ankle plantarflexion and dorsiflexion for eight minutes. In contrast to the studies above, a significant increase in neuropathic pain intensity post guided visual imagery (p<0.01).

Conclusion

There is level 1 (Soler et al. 2010) that visual illusion combined with tDCS results in improvement of post SCI pain.

There is level 2 (Jordan et al. 2016) evidence that virtual walking reduced post SCI neuropathic pain.

There is level 4 (Viliger et al. 2013) evidence that virtual reality related lower limb tasks may reduce pain post SCI.

There is level 4 evidence (Gustin et al. 2008) that visual imagery of ankle movements is not sufficient to reduce pain post SCI.