## 4 Immersive Virtual Reality: Hardware and Software Perspectives
### Overview of Immersive Virtual Reality Software  
The market for immersive VR software specifically tailored to musculoskeletal rehabilitation appears to be relatively underrepresented compared to offerings for neurological rehabilitation. This trend could be due to the higher research activity in the field of VR for neurorehabilitation, as a quick search in the PubMed database shows. Using a search string designed to capture VR applications for various neurological conditions (including terms such as: \"_VR_\", \"_virtual reality_\", \"_neuro*_\", \"_stroke_\", \"_Parkinson**_\", \"_multiple sclerosis_\", \"_brain injury_\", \"_brain damage_\", \"_CVA_\", \"_cerebrovascular accident_\", \"_spinal cord injury_\", and \"_cerebral palsy_\"), number of the results are almost four times higher than those for musculoskeletal applications (the search string for the use of VR for musculoskeletal disorders included the following terms: \"_VR_\", \"_virtual reality_\", \"_musculoskeletaltal_\", \"_orthopaedic_\", \"_neck_\", \"_back_\", \"_knee_\", \"_hip_\", \"_ankle_\", \"_shoulder_\", \"_joint replacement_\", \"_arthroplasty_\"). This discrepancy may \begin{table}
\begin{tabular}{l} \hline \hline \multicolumn{1}{c}{**Some Providers and the Price Range**} \\ \hline Providers: Meta, Pico, HTC Vive, Samsung, Vuzix, DPVR, Sony, Steam, Primax, Lenovo, Apple, Varjo. \\ Price range: Approximately 200 to 10,000 EUR. \\ \hline \hline \end{tabular}  
* Key Technical Specifications
* Resolution per eye: Provides clearer and more detailed visuals. Refresh rate: Ensures a smooth and responsive display. Field of view: Affects the level of immersion. Ability to adjust interpupillary distance: Allows customization for different eye spacing. Weight and comfort: Heavier devices may cause discomfort and pressure on the head. Battery performance: Determines how long the device can be used without recharging. Tracking capabilities: Headsets can enable full-body, eye, face, or hand tracking for enhanced movement detection. Standalone or wired: Standalone headsets offer more freedom of movement, while wired ones provide higher performance.  
\end{table} 
Table 1: Overview of VR headsets and their specifications. reflect the growing interest in VR's potential to support recovery in neurological patients, leaving musculoskeletal VR applications as a smaller, still developing field. In the treatment of patients with musculoskeletal disorders and chronic pain, a variety of VR software is used in research, with the same software rarely appearing in more than one study. This variability could be attributed, at least in part, to the possibility that some of this research is funded by technology companies developing proprietary VR systems [82]. Both commercially available applications and custom-developed programs are used in these studies. Examples of commercially available software used in research include: _ReliewVRx_ (initially named _EaseVRx_) by _AppliedVR_[49; 124; 125], guided meditation VR app by _Cubic Ninjas_[50; 95], _Karuna Virtual Embodiment Training_[102], the _COOL!_ app by _DeepStreamVR_[126], _VR TierOne_[101], _Ocean Rift_ and _Gala 360_[93], _Cred: Rise to Glory, The Avengers Powers Unite_ and _The Climb_[25]. These VR applications differ in the experiences and actions they require of users. Some software programs focus on meditation, education, and/or relaxation. _ReliewRx_, for example, is an immersive, multimodal, skills-based pain self-management program that incorporates evidence-based principles of cognitive behavioral therapy, mindfulness, and pain-neuroscience education. Other applications promote physical movement in a VR environment. _Ocean Rift_ and _Gala 360_, for example, promote neck movement by engaging the user in observing marine animals, while _Karuna Virtual Embodiment Training_ promotes physical movement in patients with upper-extremity chronic pain and is based on the principles of graded motor imagery.