# Augmented Reality in Surgical Navigation: A Review of Evaluation and Validation Metrics
## 2 State of the Art AR Based Surgical Systems
### Oral Surgery  
Oral surgery normally involves surgeries on the jaws and the teeth to alter the dentition. Drilling, cutting, fixing, resection, and implantation are the most common oral surgical procedures [69,70]. The tight space and the fact that perhaps the surgical targets may be covered, limit operations in most circumstances. To ensure surgical safety, surgeons must practice avoiding injury to the surrounding important structures. Dental surgery still experiences imperfect hand-eye coordination and a loss of 3D information in surgical navigation, despite the introduction of computer assisted oral surgery.  
Using an IV based 3D image overlay system and stereo tracking, [PERSON] and [PERSON] created a 3D augmented reality based navigation system with automatic marker-free registration of image for oral surgery [71,72]. A stereo camera for tracking patients and equipment, a real-time patient's 3D image registration method, an IV camera registration method, and an optical see-through device are all part of the proposed system [8]. The surgeon can use the AR information to intuitively examine hidden structures as well as the surgical tools. Figure 7 shows the AR model overlay with surgical scene and the surgical instrument in 3D, with an overlay showing the tool's location in pink and nerve channel in blue.  
Experiments were conducted to confirm the practicality, and the suggested system's overlay error was less than 1 mm. Surgeons can obtain intuitive depth information and then treat while using the IV based 3D AR system. Another knowledge-based strategy for a contextual intra-operative support system is presented in [73], where two phantom experiments were performed examining the medical usability, accuracy, and recognition rate. In conclusion, the system demonstrated its ability to accurately identify circumstances and give beneficial visualizations in real-time; however, issues with low accuracy continue to exist. Future research will concentrate on increasing the accuracy and recognition rate as well as assessing the concepts on complex procedures.  
To summarize, Table 1 shows the publication list where evaluation and validation studies have been performed using AR technology. The kind of evaluation being conducted varied from testing the AR system for medical imaging, training and guidance, pre-operative planning and surgical navigation. The use of AR technology for pre-clinical trials, various clinical testing and applications, and surgery on patients is also evaluated. This table makes it very evident that the majority of the applications lack a proper validation on using AR surgical technology.  
Figure 7: (**a**) A teeth model overlay with important features to show the tooth roots that are not visible; (**b**) an enhanced visual representation of the surgical tool with the drill route superimposed; (**c**) a lower jaw model was superimposed with three-dimensional photographs of molars, including a developing wisdom tooth; and (**d**) an enhanced display on the surgical tool that shows the drill path [72].