Since 1968, virtual reality technology has become an emerging technology of interdisciplinary integration after more than 50 years of development. In recent years, virtual reality technology, as a new treatment method, has been widely used in rehabilitation clinical treatment and scientific research, involving the direction of movement, sensation, and mental health, etc.

A brief introduction of virtual reality technology

Virtual Reality (VR) refers to human-computer interactive simulation jointly established by computer software and hardware to provide users with a scene that can feel and experience the simulation of the real world [1].

In the early days, virtual reality was used in training of various professions, such as flight simulation training [2] and surgical operation [3]. In the field of medical treatment, most of them are applied to emotional disorders, such as phobias [4] and post-traumatic stress syndrome [5]. In recent years, due to the accessibility and low cost of virtual reality technology, it has become more and more popular in rehabilitation medicine, but it has not become a conventional treatment for rehabilitation treatment. At present, researchers and clinicians have begun to use low-cost commercial games as an alternative to virtual reality therapy [6]. These games were originally intended for entertainment and are often individually tuned by clinicians for different therapeutic purposes. In addition, more and more interactive games for rehabilitation training are being developed and marketed by many startups [7, 8].

Compared with traditional medical means, virtual reality technology has great advantages in goal-oriented task training and repetitive functional training, and has more important significance in neurological rehabilitation [9, 10]. In some basic experiments, the researchers found that when compared with the ordinary environment, the animals showed stronger problem solving ability and better activity performance in the functional test in the rich environment (such as the virtual environment) [11]. Based on the Enriched environment provided by virtual reality, a patient with a stroke could learn to solve problems and acquire new skills in a virtual world. Children and adults describe virtual tasks as more interesting and enjoyable than traditional target training, thus attracting them to engage in more repetitive training [12]. So far, another benefit of virtual reality remains underutilized, with clinicians able to perform functional tests that would be relatively dangerous in the real world, such as crossing the road. In addition, some virtual programs can be trained without medical personnel, which can both reduce the number of medical personnel and increase the intensity of patient training and speed recovery.

2. Theoretical basis of virtual Reality technology

In virtual rehabilitation, patients can create visual feedback on virtual scenes and objects through a head-mounted device, projection system or flat screen. Such a visual feedback can also be conducted by senses such as hearing, touch, movement, balance and smell [1]. The interaction between patients and the virtual environment is mainly realized through various sensing devices. Simple devices include mouse, handle, lever, tracker, etc., while complex devices include camera for motion capture, gesture recognition system, inertial sensor, odor player, force feedback simulator, etc. [1]. Thus, the intensity of a patient's activity can vary depending on the intensity of the intervention from low-intensity activities (e.g., sitting at a computer with a mouse) to high-intensity activities (e.g., whole-body coordination), enabling individualized treatment.

Immersion is an important factor to be considered in the application of virtual reality technology in the field of rehabilitation. The sense of immersion refers to the degree of difference between the virtual environment and the real world perceived by patients. The stronger the sense of immersion, the lower the degree of difference between the virtual and real world perceived by patients will be. The intensity of immersion is related to both hardware and software. For example, when the virtual environment is displayed through a projector or a desktop display, the user is required to always look at the front screen, which cannot simulate the real man-machine interaction, so the immersion is lower than that of VR headset. The gesture recognition system has more advantages than the handle in the aspect of human-computer interaction reality. VR headsets with six degrees of freedom are more immersive than VR headsets with three degrees of freedom. The image delay is lower than the perception level, which can make the user's sense of ontology and vision more unified. The more realistic the image quality of virtual environment is, the stronger the user's sense of immersion will be [1, 13, 14].

3 evidence-based support of virtual reality therapy in rehabilitation therapy

Virtual reality technology is currently used for the evaluation and treatment of neurological diseases and injuries, such as stroke, spinal cord injury, Parkinson's disease and cerebral palsy.

3.1 Alzheimer's Disease

Virtual reality is an effective tool for screening for the early signs of Alzheimer's disease, as well as distinguishing between different stages of cognitive impairment. According to research by Werner et al. [15], VIRTUAL reality can also expand and deepen our understanding of diseases by using immersive tasks to collect and buy some products in virtual supermarkets. Under Mild cognitive impairment (MCI), the subjects were compared between healthy elderly people and those with Mild cognitive impairment (MCI). Both patients' paths were compared, and both pauses and mistakes (such as choosing the wrong product or quitting for nothing) were compared. When most participants completed the task, differences (duration, distance, and error rate) occurred during the process. All of these variables were significantly poorly assessed in MCI patients, thus demonstrating the sensitivity of virtual reality tools. These results were similar to those assessed by the MMSE (Mini-mental State Examination).

3.2 Stroke

At present, virtual reality has certain therapeutic effects on the function of the upper limbs and daily life of stroke patients. Systematic analysis by Laver et al. [16] published in Cochrane Database showed that the use of VR did not improve upper limb function when compared with traditional treatments (standardized mean difference of 0.07, 95% confidence interval of -0.05 to 0.20, 22 studies, 1038 subjects, poor quality of evidence). However, when virtual reality is combined with routine treatment or rehabilitation training, patients can achieve more significant upper limb functional recovery by increasing their training time (standardized mean difference 0.49, 95% CONFIDENCE interval 0.21 to 0.77, 10 studies, 210 subjects, poor quality of evidence). When compared with the traditional treatment, virtual reality display group gait speed and improvement of balance was not statistically significant, but the daily Activities Activities (Activities of daily living, ADL) function (such as bathing and dressing) showed a statistically significant increased significantly (standardized mean difference 0.25, 95% confidence interval, 0.06 to 0.43, 10 studies, 466 participants, moderate quality evidence). At present, the quality of evidence related to the therapeutic effect of virtual reality on stroke patients needs to be improved, which may be mainly due to the lack of sample size. The evaluation index is not uniform; There are obvious differences in research methods.

3.3 Spinal Cord Injury

Virtual reality therapy can improve balance and gait in patients with spinal cord injury. A recent systematic review and meta-analysis by Abou et al. [17] found that virtual reality plus conventional therapy effectively improved posture balance compared with conventional therapy alone (standardized mean difference =1.65, 95% confidence interval =1.21 to 2.09, P <0.01, 3 randomized studies). A meta-analysis of 7 pre- and post-control studies showed that VIRTUAL reality therapy alone was effective in improving balance standing (mean =8.53, 95% CONFIDENCE interval =2.52 to 14.53, P =0.01) and effective gait improvement trends (standardized mean difference =0.34, 95% confidence interval =0.02 to 0.66, P =0.04). These studies are based on preliminary data and only a small number of randomized controlled trials.

3.4 Parkinson Disease

Albani et al. applied the rehabilitation system built by virtual reality technology to the cognitive function screening of Parkinson's patients [18]. The study showed subjects simple tasks in virtual reality to see how they could Orient themselves spatially and interact with the virtual environment. Later, I also tried to apply the Virtual multiple Error test (VMET) to assess the decision-making ability of Parkinson's patients, so as to find the correlation with sleep dysfunction [19].

Virtual reality therapy will be a potential new form of intervention that can be used to improve balance in Parkinson's patients. The meta-analysis of Chen et al. [20] found that compared with active therapy, virtual reality therapy could significantly improve the Berg Balance Scale (mean =1.23, 95% confidence interval =0.15 to 2.31; I2=56%, medium quality) functional performance. In addition, the sensitivity analysis found that VIRTUAL reality therapy improves Dynamic Gait Index and Functional Gait Assessment (mean =0.69, 95% Confidence interval =0.12 to 1.26). I2=0%, medium quality). However, virtual reality therapy showed no statistically significant improvement for the Timed Up and Go test (TUG) and the Activity-specific Balance Confidence scale. Although the above scale or found statistically significant in the test, but failed to meet minimum clinical significance change value (Minimal clinically important difference, MCID), that is to say, the clinical practical value still need further discussion.

3.5 Cerebral Palsy (Copalsy)

Preliminary evidence suggests that virtual reality therapy can improve gait rehabilitation in children with cerebral palsy. A meta-analysis by Ghai et al. [21] (16 studies, 274 children) found that Gait Velocity, Hedge's g=0.68), Stride length, Hedge's g=0.30, The correlation between Cadence (Hedge's g=0.66) and Gross motor function measure (Hedge's g=0.44) was statistically significant. Subgroup analysis found that the duration of each training was 20-30 minutes, the number of training times per week was less than or equal to 4 times, and the 8-week virtual reality therapy could improve the walking speed of children with cerebral palsy to the greatest extent.

4. Prospect of virtual Reality technology

Can be seen from the current clinical application and the research trend, virtual reality technology is becoming more and more widely applied in the field of rehabilitation, but the research evidence is still relatively lack, especially lack of multicenter, large sample randomized controlled clinical research, many systematic review or meta-analysis have found that most of the current research of heterogeneity is bigger. Most studies have shown that virtual reality does not have better clinical efficacy than traditional rehabilitation methods. However, the results were equivalent to those of traditional rehabilitation methods. This suggests that the virtual reality technology may not be used to replace traditional methods of rehabilitation, but as a beneficial supplement, to the value of virtual reality applications in the field of rehabilitation can not only around the clinical curative effect, should also develop other areas, including health economics analysis, patients experience, and compliance, manpower and equipment cost analysis, community and family support and other traditional rehabilitation method is difficult to carry out the direction.

reference

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