Evaluating a Novel 3D Stereoscopic Visual Display for Transanal Endoscopic Surgery

A Randomized Controlled Crossover Study

Aimee N. Di Marco, MA, MBBS, MRCS; Jenifa Jeyakumar, BSc; Philip J. Pratt, PhD; Guang-Zhong Yang, FREng; Ara W. Darzi, MD, FRS, FMedSci, FRCS, FACS


Annals of Surgery. 2016;263(1):36-42. 

In This Article


Studies to date have compared single 3D systems against a single 2D system, whereas, this study has shown, what has long been suspected clinically, that not all 3D displays are equal: although 2 of the 3D modalities—the stereoendoscope and novel 3D box viewer—performed equally well, both significantly outperformed the third 3D modality of a monitor with polarizing glasses. Previous reports have stated that polarizing modalities can potentially render poor transmission and images can appear dark as the intensity of light emitted is often quite low.[20] In this case, the better performing systems were both stereoscopic in nature and the inferior 3D system was a monitor with passive polarizing glasses (a high-quality 1920 × 1080 HD monitor).

The equivalent performance of the novel box viewer and stereoendoscope in terms of primary outcome measures is very positive for the novel viewer, as the Wolf stereoendoscope is highly regarded in the clinical community and remains the most commonly used platform for TES.

It is possible that there may be some subtle differences in performance metrics between the box viewer and stereoendoscope, which were not detected: for instance, the novice subgroup did show an improvement in accuracy when using the box viewer as compared with the stereoendoscope (Fig. 6). This was the largest subgroup; therefore, it is possible that the intermediate and expert groups (of 11 and 5, respectively) were not of sufficient size to detect this difference.

An alternative explanation is that the equivalent performance is attributable to the experience of the intermediate and expert groups with the stereoendoscope in clinical practice. Task workload does seem to have been affected by the level of experience: in the intermediate and expert subgroups, it was not significantly different between the 2D screen and the 3D box viewer, which may be because experienced surgeons were able to detect subtle monocular depth cues in the 2D screen. However, workload when using the 2D HD screen was significantly higher in the intermediate group compared to the expert group, perhaps showing the effect of intense training, over a number of years, needed to reach proficiency and comfort with a standard 2D screen in laparoscopy. The differences between the subgroups with the 3D box viewer were smaller and less variable, suggesting that it may compensate in some way for inexperience and may flatten the learning curve.

One unexpected result was that, in the novice subgroup, the 3D screen was actually found to be inferior to the 2D screen. One potential reason for this is that this group contained 5 individuals with astigmatism. Post hoc analysis of the questionnaires showed that these individuals consistently provided negative feedback regarding the 3D screen and, on exclusion of these individuals, significance was not reached in the comparison between 3D monitor and 2D. It is possible that the participants' corrective lenses interfered in some way with the polarizing glasses used with the 3D screen. This suggests that astigmatism, and other refractive errors, may need to be considered in the future development of 3D visual display systems. A subject's binocular vision, or lack thereof, would be expected to affect their ability to visualize 3D images regardless of the modality. Two percent of the population lack binocular vision entirely and 15% to a lesser degree;[25] however, all participants in this study were found to have binocular vision. This is not unexpected, given that there may have been some selection bias, with participants either already working as surgeons, and medical students who self-selected to enter a "surgical" study.

Recognized limitations of the study included the differing sample size and sex mix for each subgroup (Table 1). However, there was enough power to show a significant difference in primary outcomes in all 3 subgroups. An attempt was made to limit any change in performance due to the Hawthorne effect,[31] generated by the presence of the researchers in the room: by ensuring no intervention from the researchers and using the discrete Aurora EM tracker to monitor instrument path length. Ideally, a full simulation of a TES polyp excision would have been conducted, indeed, one might expect to see more profound differences in the results with a task more dependent on depth perception. Prior work on methods of best simulating TES showed that this was the most appropriate mode, with the animal tissue allowing a view and dissection with some realism. Indeed, feedback from the participants regarding the simulation was very favorable, scoring between 80% and 100% in the simulation questionnaire and confirming its face validity. Furthermore, construct validity was evident as time taken, path length, and perceived task workload significantly decreased with increasing experience from novices to intermediate to expert (Figs. 4–7). Consistency in the objective measurements across the 3 tasks for each visual display was high, showing minimal learning effect. The interrater reliability, as determined by the Kappa measure of agreement showed no significant difference in accuracy.

Despite these minor limitations, the novel 3D box viewer was shown to improve surgical performance in TES simulation, providing a high-quality image in an immersive and ergonomically favorable environment. No other stereoscopic system currently available meets all of these criteria. Although the traditional Wolf 3D stereoendoscope performed well, it has significant ergonomic issues, with the box viewer being rated more favorably in this regard. A potential future benefit of this system is that, unlike with the direct line-of-sight Wolf stereoendoscope, image augmentation with overlay of pre- or intraoperative imaging may be done with the box viewer. This feature has been shown to be beneficial in some studies using the daVinci robot.[32,33] Additional 2D screens for assistants and nurses can also be connected, in the same way as with the standard stereoendoscope, by sharing the feed from the camera, which is paramount for the safety of the patient.

Use of the 3D box viewer may increase the adoption of TES by reducing the learning curve of trainee surgeons. An optimal visual display system is not a substitute for high technical skill but will aid the development of these skills in a more favorable environment. It is possible that use of the box viewer by those already carrying out TEMS with the stereoendoscope may shorten operating times; a preliminary, unpublished study conducted by our group found that surgeon discomfort with the stereoendoscope resulted in them breaking their operating posture around 12 times during a 45-minute case [diMarco 2013]. While the visual quality of the Intuitive Surgical da Vinci system, used by some to carry out TES, is undoubtedly good, the system is expensive to acquire and maintain, whereas this simple addition to the platform costs a maximum of £2000 (likely to be less if it were to be manufactured in large numbers). As with the use of standard Storz camera heads in current clinical practice, these are not sterilized, but are shielded by a sterile drape. The same drape can be used to enclose the paired Storz camera heads used in this experiment, allowing immediate and safe clinical translation of the system.

At the time of writing, the box viewer has been used in 5 TES procedures on patients, with all being completed successfully. Following on from this clinical feasibility study, a randomized clinical multicenter trial will be required to evaluate the clinical effect of the box viewer. Reproduction of the box viewer to permit such a study is expected to be fairly straightforward and, as above, inexpensive.

Ultimately, improvements in the visualization for TES are likely to form 1 crucial component in a holistic approach to system improvement, which is also likely to address the limitations of operative tools, the mounting system, and to include additional augmented reality imaging.