19

Evaluating a novel 3D stereoscopic visual display

for

Transanal Endoscopic Surgery:

A randomised controlled cross-over study

Aimee N. Di Marco MA MBBS MRCS1, Jenifa Jeyakumar BSc2, Philip J. Pratt PhD1,Guang-Zhong Yang FREng 1, Ara W. Darzi MD, FRS, FMedSci, FRCS, FACS1,3

(1) Hamlyn Centre for Robotic Surgery, Imperial College, London, UK

(2) Guy’s King’s & St. Thomas’ School of Medicine, King’s College, London, UK

(3) Department of Surgery & Cancer, Imperial College, London, UK

Corresponding author:

Aimee N. Di Marco

Hamlyn Centre for Robotic Surgery

Imperial College

Floor 3, Patterson Centre

St. Mary’s Hospital

London W2 1NY

Email: a.di-marco@imperial.ac.uk

Tel: +44 (0) 203 312 5518

Fax: +44 (0) 203 312 6309

Conflicts of interest and sources of funding

Aimee di Marco conducted this study during a research fellowship funded by Cancer Research UK and the Rosetrees trust (grant number C37990/A12990).  The study was performed as part of a project grant from the Wellcome Trust & Department of Health (HICF-T4-299).  The research was supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Imperial College Healthcare NHS Trust and Imperial College London. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.  The authors wish to thank all of these institutions for their support.

Running headComparing visual display systems for transanal endoscopic surgery

Mini Abstract

A randomised, controlled, cross-over study evaluating a novel 3D stereoscopic visual display against current 2D and 3D alternatives in an ex-vivo Transanal Endoscopic Surgery (‘TES’) simulator.

Abstract

Objective: To compare surgical performance at TES using a novel 3D stereoscopic viewer against the current modalities of a 3D stereoendoscope, 3D and 2D HD monitors.

Summary Background Data TES is accepted as the primary treatment for selected rectal tumours. Current TES systems offer a 2D monitor, or 3D image, viewed directly via a stereoendoscope, necessitating an uncomfortable operating position. To address this and provide a platform for future image augmentation, a 3D stereoscopic display was created.

Methods: 40 participants, of mixed experience level, completed a simulated TES task using four visual displays (novel stereoscopic viewer and currently utilised stereoendoscope, 3D and 2D HD monitors), in a randomly allocated order. Primary outcome measures were; time taken, path length and accuracy. Secondary outcomes were; task workload and participant questionnaire results.

Results: Median time taken and path length were significantly shorter for the novel viewer versus 2D and 3D, and not significantly different to the traditional stereoendoscope. Significant differences were found in accuracy, task workload and questionnaire assessment in favour of the novel viewer, as compared to all 3 modalities.

Conclusions: This novel 3D stereoscopic viewer allows surgical performance at TES, equivalent to that achieved using the current stereoendoscope and superior to standard 2D and 3D displays, but with lower physical and mental demand for the surgeon. Participants expressed a preference for this system, ranking it more highly on a questionnaire. Clinical translation of this work has begun with the novel viewer being used in five TES patients.

Introduction

Transanal Endoscopic Surgery

Colorectal cancer is the fourth most common malignancy worldwide,1 with rectal cancer accounting for over a third of these. Local transanal excision is an important alternative to radical surgical approaches to the rectum, i.e. anterior resection and abdominoperineal excision, for selected early cancers of the mid and upper rectum, as it offers reduced operative time, fewer complications, less post-operative pain and a shorter recovery period.2-10 In addition, TES is considered the gold standard for treatment of benign rectal adenomas, which cannot be excised endoscopically, and which risk malignant transformation if left behind, and has an important role in the non curative excision of advanced malignancies for palliation of symptoms and disease control in very co-morbid patients.10-12 The adoption of screening programs13 for colorectal cancer, improved tumour downstaging with novel neoadjuvant therapies14 and an increasingly elderly and frail population, are likely to make minimally invasive procedures, such as TES, increasingly important in the future.

The original platform, known as ‘Transanal Endoscopic Microsurgery’ (‘TEMS’)15 was pioneered by Dr. Gerhard Buess and developed with Richard Wolf GmBH in the 1980s: this platform has changed little since its inception, but despite this, and competition from newer systems such as Karl Storz’s ‘Transanal Endoscopic Operating’ system (‘TEO’), and the rise of ‘Transanal Minimally Invasive Surgery’ (‘TAMIS’) using either standard laparoscopic instruments via a single incision (‘SILS’) port or robotically with the daVinci Si,16, 17 the Wolf TEMS system has remained the most widely used. All of the platforms available for TES require a high degree of technical skill to overcome the issues of lack of triangulation and instrument clashes in the small workspace, and achieve a complete resection with clear margins: this is of paramount importance as salvage surgery for positive margins or local recurrence is associated with a worse prognosis than primary radical surgery.18 In light of the potential growth of TES, improvements in any such system are required. This project sought to identify and improve upon the key area of visualisation.

The Wolf TEMS system has a custom stereoendoscope, which offers a high quality magnified 3D image of the operative field. The superior visualisation afforded by this stereoendoscope is one reason for the system’s continued popularity. However, a major associated drawback is that the operator can only obtain this image by viewing directly into the stereoendoscope, requiring the adoption of an uncomfortable position of neck flexion. An ancillary, ‘teaching’ port on the stereoendoscope can be utilised to provide an image to a 2D flat screen for other personnel in the operating theatre. Many experienced surgeons will therefore choose to operate using this 2D flat screen instead and switch to the stereoendoscope only if the procedure becomes challenging. This study sought to establish the relative merits of these two approaches against a novel 3D stereoscopic viewer and a flat 3D screen.

Creation of a novel 3D stereoscopic viewing device

A novel 3D stereoscopic viewer was designed and built, based on the principles of the ‘Wheatstone stereoscope’ (figure 1).19 A pair of high definition (‘HD’) laparoscopic camera heads (Storz UK Ltd) were mounted, with a custom-made bracket, onto the Wolf TEMS Stereoscope, to provide independent outputs to two small video monitors (5.6” TVLogic VFM-056W 1280x800). The monitors, with paired mirrors and lenses were mounted on a machined aluminium plate and suspended from a stainless steel frame (Gallops UK) (figure 1). This configuration of components in a box shape gave rise to its nickname amongst study participants, the ‘box viewer’, which is used during this paper.

The effect of the dual screens and mirrors, which is also utilised in Intuitive Surgical’s daVinci console, is to mimic the most salient physiological depth cue of binocular disparity,20, 21 creating the illusion of a 3D object without the need for polarizing glasses.22 This creates an immersive environment, which has previously been shown to benefit surgical performance.23

Previous work on 3D displays in surgery

The work of previous groups on 3D surgical displays has shown that first generation systems were associated with visual strain, headache and facial discomfort.24 However, improved second generation systems have shown some benefits in ex-vivo tasks.25, 26 Technical issues which can result in a suboptimal image include cross-talk between the two images of a stereoscope, which can be perceived as ‘ghosting’ (a faint duplicate image), flicker and vertical disparity, and lead to eye strain, when continued compensation is required.22, 26 The development of 3D displays is further burdened by their inherent removal of a number of other depth cues such as accommodation and motion parallax.22, 24, 26

This is the first TES-specific study on 3D visualisation and examines the performance of the novel stereoscopic 3D ‘box’ viewer against the traditional Wolf stereoendoscope and standard 2D HD and 3D HD monitors. A pilot study of ten surgeons was performed prior to the full study and showed superior performance with the box viewer on a standardised peg transfer model.

Methods

This study was informed by its pilot, with participants performing the ex-vivo TES task in four different visual modalities (Wolf stereoendoscope, novel box viewer, 2D HD and 3D HD monitor with polarising glasses), acting as their own controls and crossing over to each modality in a randomly allocated order in to minimise any learning effect. As a randomised trial, the study was registered with CONSORT (the Consolidated Standards of Reporting Trials).

Study Participants

Participants were recruited from the staff of a 1500-bedded group of 3 acute, teaching hospitals in London, UK, and medical students from that institution’s Bachelor of Science programme. Males and females ranging in experience from novices to consultant colorectal surgeons were included. All subjects were screened for stereoscopic vision27 and were excluded if the test was failed.

Task

The first operative step of a TES procedure was simulated using ex-vivo porcine colon, containing a synthetic polyp consisting of plastic material interposed between a dual layer of porcine bowel. These ‘polyps’ were of a standardised size (median 35mm, IQR 34-37mm) and, so as to guide the subjects to the intended surface boundary of the lesion and allow judgement of accuracy, the surface of the porcine bowel was marked with twelve circumferential ‘tattoos’ in permanent marker ink (figure 2a).

This porcine colon was placed within a phantom pelvis with lower limbs in the lithotomy position, as if excision of a posterior rectal tumour were to be performed (the most common location for lesions managed with TES). Participants were given an angled, toothed grasper and pedal-operated diathermy wand (TEO, Storz UK Ltd), on the tip of which was mounted an electromagnetic tracker (Aurora™, Northern Digital). They were asked to score around the lesion as in the first step of a TES procedure. The set-up, including endoscope position, illumination, distance between specimen and endoscope, and between viewing device and subject remained constant throughout the study, with participants being able to adjust the variables which would usually be dictated by the surgeon; the height of the operating table and chair, inter-ocular distance of the stereoendoscope and placement of the instruments in left versus right hands. Four different visual displays were utilised: an LG HD 2D 1920x1080 monitor, LG 3D HD 1920x1080 with passive polarising glasses, Wolf 50° 3D stereoendoscope, and the novel stereoscopic ‘box viewer’.

Procedure

Figure 3 shows the pathway of each participant through the study: written consent to participate was gained, a short, standardised explanation of TES and the task was given, and the stereopsis-screening tool administered.27 No participants failed this test. All then completed a pre-test questionnaire to determine level of experience, visual acuity and presence of colour vision. Participants were then allowed to practise the task until a pre-determined level of proficiency was achieved. Once proficiency was reached, participants completed the task three times using each visual display modality. The order of the visual displays was randomised to negate any learning effect.28 After completing the task three times on a particular display, participants answered a NASA-TLX questionnaire29 and moved on to the next display. After a total of 12 tasks a post-test questionnaire was completed to collect feedback on the subjects’ opinions of the visual displays and to assess face validity of the simulation.

Primary outcome measures

Primary outcomes were path length, accuracy, time taken and task workload, compared between the four visual displays and for subgroups based on the experience level of the participants (assessed on the pre-test questionnaire). The path length of the diathermy wand was deduced from three vector coordinate data generated by the Aurora™ electromagnetic tracker. Accuracy was assessed by end-product analysis of each specimen, conducted by two blinded assessors (AdM and JJ), measuring distance between diathermy mark and target tattoo to the nearest half millimetre. Time taken for each task was obtained from the duration of each video file to centiseconds accuracy. The perceived workload of the three tasks performed with each modality was assessed by the participant using the NASA-TLX questionnaire29 which uses pair-wise comparisons to generate a weighted score between 0-100 (where 100 indicates a higher workload) based on the contribution of mental, physical and temporal demand, performance, effort and frustration to the task. The pilot study of 10 participants was used to inform a power calculation, which dictated a minimum sample size of 25 participants. Although the assessors were blinded to the modality, it was not possible to conceal the type of display system being used from the participant.

Secondary outcome measures

Participant opinion regarding each of the imaging modalities was assessed using a custom-designed questionnaire, in which each modality was ranked across 5 domains; image quality, visual discomfort, depth perception, ergonomics and overall preference, using a Likert scale of 1-10 and an opportunity for free text. The questionnaire also assessed face validity of the simulation using the same Likert scale across seven domains; realism of the overall set-up, the tissue, task, instruments, clinical scenario, perception of whether the simulation would improve performance and interest in using the simulator in the future.

Errors during tasks, defined as inadvertent diathermy swipes or failing to mark at a tattoo were recorded. However, the trial was not powered to analyse such errors.

Statistical Analyses

Primary outcome measures were assessed using median values and inter-quartile ranges calculated using the SPSS statistics package for Windows, version 20.0.30 Pair-wise comparisons between the four modalities and within the experience subgroups were calculated using Wilcoxon’s matched-pair signed-rank test for non-parametric data. Inter-rater reliability of the assessors’ measuring accuracy was determined using the same methodology. Secondary outcome measures were also expressed as median and interquartile ranges and, where relevant, comparisons were made using Wilcoxon’s matched-pair test. The significance level was set at p-value <0.05 for all outcomes.

Results

Forty participants completed the study. Table 1 shows their demographics. Novices were defined as those without any experience as primary operator or assistant in laparoscopy, TES, robotics or SILS. Intermediates were laparoscopic surgeons with no primary operator experience in TES or SILS. Experts were senior registrars and consultant surgeons with primary operator experience in TES and /or SILS. Experience in SILS was judged as relevant owing to the cross-over in skills requirement between the two.

Primary outcomes

Time taken and path length were significantly reduced with the 3D box viewer, compared to 2D and 3D screens, and were not significantly different from the stereoendoscope (table 2, figure 5 & 6). Accuracy was significantly improved and task workload was significantly reduced with the 3D box viewer compared to the three other modalities (table 2, figure 7 & 8).

Secondary outcomes

The 3D box viewer performed best on the post-test questionnaire (figure 4) with best image quality, depth perception, least visual discomfort (jointly with the 2D monitor) and five and a half fold and two and a half fold decrease in discomfort in comparison to the 3D screen and stereoendoscope respectively (p~0.00, p=0.01). Overall ergonomics were judged to be similar for the 3D box viewer, 2D and 3D monitors ergonomics (all median scores 8), but significantly superior to the 3D stereoendoscope with median score of 6 (p~0.00). Subjects expressed a preference for the 3D box viewer for potential future clinical use.

The number of errors did not differ across the visual display systems, but the study was not powered to examine this and the overall number of errors was insufficient for meaningful comparison. Face validity of the simulated TES scenario, assessed using the post-test questionnaire was high (mean score 60.5/70 i.e. 86%).

Subgroup analyses

Novices, intermediates and experts showed the same trends and significant differences in primary outcome measures of time taken and path length. The novice subgroup performed slightly differently from the intermediates and experts in accuracy and workload: accuracy (measured as deviation from the tattoo) was not significantly different for experts and intermediates between the 3D box viewer and 3D stereoendoscope, but in the novice group, was significantly better with the box viewer in comparison to all three other modalities (figure 7). The novices showed significantly lower task workload with the 3D box viewer in comparison to all three other modalities, however the intermediates and experts only showed a significant reduction in workload between box viewer and 3D HD monitor (figure 8).

Interestingly, in secondary outcomes, the novices showed less discrimination between the image quality of the 3D stereoendoscope and 3D box viewer reported on the post-test questionnaire.

Discussion

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: while two 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 polarising glasses. Previous reports have stated that polarising 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 polarising glasses (a high quality 1920x1080 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 (figure 7). This was the largest subgroup, hence 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 due 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 due to experienced surgeons being 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 polarising 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 visualise 3D images regardless of the modality. 2% of the population lack binocular vision entirely and 15% to a lesser degree25 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.

Recognised limitations of the study included the differing sample size and gender mix for each subgroup (table 1). However, there was enough power to show a significant difference in primary outcomes in all three subgroups. An attempt was made to limit any change in performance due to the Hawthorne effect31 generated by the presence of the researchers in the room; by ensuring no intervention from the researchers and utilising the discrete Aurora EM tracker to monitor instrument path length. Ideally, a full simulation of a TES polyp excision would have been performed, 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 favourable, scoring between eighty and a hundred percent 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 (figures 5-8). Consistency in the objective measurements across the three tasks for each visual display was high, showing minimal learning effect. The inter-rater 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 favourable environment. No other stereoscopic system currently available meets all these criteria. Although the traditional Wolf 3D stereoendoscope performed well, it has significant ergonomic issues, with the box viewer being rated more favourably 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 performed 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 favourable environment. It is possible that use of the box viewer by those already performing TEMS with the stereoendoscope may shorten operating times; a preliminary study performed by our group found that surgeon discomfort with the stereoendoscope resulted in them breaking their operating posture around twelve times during a forty five minute case [diMarco 2013]. While the visual quality of the Intuitive Surgical da Vinci system, used by some to perform 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 sterilised, 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 randomised clinical multicentre trial will be required in order 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 visualisation for TES are likely to form one crucial component in a holistic approach to system improvement, which is also likely to address the limitations of operative tools, mounting system and to include additional augmented reality imaging.

Conclusion

The novel 3D box viewer, developed by the authors, has been objectively shown to improve surgical performance in a simulated TES scenario across all levels of experience. This study has highlighted the importance of different modes of displaying 3D images and is the first to directly compare different stereoscopic displays. Future developments for the box viewer include further improvements in the ergonomics by suspending it from an overhead boom arm. Five clinical TES cases have already been performed at our institution using this box viewer, as part of a pilot study, however, further use in the operating theatre with detailed assessment will, of course, be required in the future.

Acknowledgements

The authors would like to acknowledge the volunteers who kindly gave up their time to take part in the study. 

References

1. IARC. Section of Cancer Information [database online]. Globocan 2008. Available at: http://globocan.iarc.fr/factsheets/populations/factsheet.asp?uno=900#BOTH. Accessed July 31st 2013

2. Middleton PF, Sutherland LM, Maddern GJ. Transanal endoscopic microsurgery: a systematic review. Diseases of the Colon and Rectum 2005; 48: 270-84

3. Kumar AS, Coralic J, Kelleher DC, et al. Complications of transanal endoscopic microsurgery are rare and minor: a single institution's analysis and comparison to existing data. Diseases of the Colon & Rectum 2013; 56:  295-300

4. Mentges B, Buess G, Effinger G, et al. Indications and results of local treatment of rectal cancer. British Journal of Surgery 1997; 84: 348-51

5. Baatrup G, Breum B, Qvist N, et al. Transanal endoscopic microsurgery in 143 consecutive patients with rectal adenocarcinoma: results from a Danish multicenter study. Colorectal Disease 2009;11: 270-5

6. Bretagnol F, Merrie A, George B, et al. Local excision of rectal tumours by transanal endoscopic microsurgery. British Journal of Surgery 2007; 94: 627-33

7. Lezoche G, Guerrieri M, Baldarelli M, et al. Transanal endoscopic microsurgery for 135 patients with small nonadvanced low rectal cancer (iT1-iT2, iN0): short- and long-term results. Surgical Endoscopy 2011; 25: 1222-9

8. Ramirez JM, Aguilella V, Valencia J, et al. Transanal endoscopic microsurgery for rectal cancer. Long-term oncologic results. International Journal of Colorectal Disease 2011; 26: 437-43

9. Buess G, Kipfmüller K, Ibald R, et al. Clinical results of transanal endoscopic microsurgery. Surgical Endoscopy 1998; 2: 245-50

10. Zacharakis E, Freilich S, Rekhraj S, et al. Transanal endoscopic microsurgery for rectal tumors: the St. Mary’s experience. The American Journal of Surgery 2007;194: 694-8

11. Sutton CD, Marshal L-J, White SA, et al. Ten-Year Experience of Endoscopic Transanal Resection. Annals of Surgery 2002; 235: 355-362

12. Türler A, Schäfer H, Pichlmaier H. Role of Transanal Endoscopic Microsurgery in the Palliative Treatment of Rectal Cancer. Scandinavian Journal of Gastroenterology 1997; 32: 58-61

13. Atkin WS, Cook CF, Cuzick J, et al. Single flexible sigmoidoscopy screening to prevent colorectal cancer: baseline findings of a UK multicentre randomised trial. Lancet 2002; 359: 1291-1300

14. Glynne-Jones R, Hughes R. critical appraisal of the ‘wait and see’ approach in rectal cancer for clinical complete responders after chemoradiation. British Journal of Surgery 2012; 99: 897-909

15. Buess G, Kipfmüller K, Hack D, et al. Technique of transanal endoscopic microsurgery. Surgical Endoscopy 1988; 2:  71-5

16. Hompes R, Ris F, Cunningham C, et al. Transanal glove port is a safe and cost-effective alternative for transanal endoscopic microsurgery. British Journal of Surgery 2012; 99: 1429-35

17. Rimonda R, Arezzo A, Arolfo S, et al. TransAnal Minimally Invasive Surgery (TAMIS) with SILS™ Port versus Transanal Endoscopic Microsurgery (TEM): a comparative experimental study. Surgical Endoscopy 2013; 27: 3762-8

18. Morino M, Allaix M,E, Arolfo S, et al. Previous transanal endoscopic microsurgery for rectal cancer represents a risk factor for an increased abdominoperineal resection rate. Surgical Endoscopy 2013; 27: 3315-3321

19. Kollin J, Hollander A,H. Re-engineering the stereoscope for the 21st century. Proc.SPIE [serial online]. March 2007; DOI: 10.1117/2.1200702.0673

20. McAllister DF. Stereo & 3D Display Technologies, Display Technology. In: Hornak JP (ed). Encyclopedia of Imaging Science and Technology, 2 Volume Set. 2 New York: Wiley & Sons; 2002: 1327-44

21. Held RT, Hui TT. A guide to stereoscopic 3D displays in medicine. Academic Radiology 2011;18: 1035-48

22. Dodgson NA, Wiseman NE, Lang SR, et al. Autostereoscopic 3D Display in Laparoscopic Surgery (conference abstract). Computer Assisted Radiology 1995; 1139-1144

23. Taffinder N, Smith SGT, Huber J, et al. The effect of a second-generation 3D endoscope on the laparoscopic precision of novices and experienced surgeons. Surgical Endoscopy 1999; 13: 1087-92

24. Hanna GB, Shimi SM, Cuschieri A. Randomised study of influence of two-dimensional versus three-dimensional imaging on performance of laparoscopic cholecystectomy. The Lancet 1998; 351: 248-51

25. Falk V, Mintz D, Grunenfelder J, et al. Influence of three-dimensional vision on surgical telemanipulator performance. Surgical Endoscopy 2001; 15: 1282-8

26. Banks MS, Read JC, Allison RS, et al. Stereoscopy and the Human Visual System. Society of Motion Picture and Televison Engineers Motion Imaging Journal 2012; 121: 24-43

27. Stereoscopic screening tool at: http://www.mediacollege.com/3d/depth-perception/test.html. Accessed September 4th 2013

28. Second generator randomization with balanced permutations [online computer program] at: http://www.randomization.com. Dallal G. 2008. Accessed April 2nd 2013.

29. Hart SG & Staveland LE. Development of NASA-TLX (Task Load Index): Results of empirical and theoretical research. In: Hancock PA and Meshkati N (Eds). Human Mental Workload. Amsterdam: North Holland Press; 1988

30. IBM SPSS Statistics for Windows [computer program]. Version 20.0. Armonk NY: IBM Corp; 2011

31. McCarney R, Warner J, Iliffe S, et al. The Hawthorne Effect: a randomised, controlled trial. BMC Med Res Methodol [serial online]. 2007; 7: 30. doi:10.1186/1471-2288-7-30

32. Volonté F, Buchs NC, Pugin F, et al. Augmented reality to the rescue of the minimally invasive surgeon. The usefulness of the interposition of stereoscopic images in the daVinci robotic console. The International Journal of Medical Robotics and Computer Assisted Surgery 2013; 9: e34-8

33. F, Buchs NC, Spaltenstein J, Hagen M, et al. Console-Integrated Stereoscopic OsiriX 3D Volume-Rendered Images for da Vinci Colorectal Robotic Surgery. Surgical Innovation 2013: 20; 158-632

Table and Figure Legends

Table 1: Demographics of the study participants

Table 2: Results of the primary outcome measures

Figure 1: The novel 3D stereoscopic ‘box viewer’. The upper image shows the external view of the complete viewer suspended from its custom built frame. The lower image shows an internal view of a CAD model of the viewer, with one of the monitors and lenses removed for clarity.

Figure 2: a; porcine colon containing synthetic polyp and with circumferential ‘tattoo’ markings b; a participant with the simulated patient in lithotomy position.

Figure 3: Flowchart showing progress of recruits through the study

Figure 4: Results of the post-test questionnaire on subjective opinion of different qualities of the four visual displays

Figure 5: Subgroup analysis of time taken by each group

Figure 6: Subgroup Analysis of path length

Figure 7: Subgroup analysis: accuracy (distance from cautery to target point to nearest 0.5mm)

Figure 8: Subgroup analysis: Task Workload Index (as quantified by the NASA-TLX)

Table 1: Demographics of the study participants

* significant difference to 3D Box Viewer

Table 2: Results of the primary outcome measures

Aluminium base plate

One of the two video monitors

Paired lenses

One of the two video monitors

Mirror

One of the paired lenses

Aluminium base plate

Figure 1: The novel 3D stereoscopic ‘box viewer’. The upper image shows the external view of the complete viewer suspended from its custom built frame. The lower image shows an internal view of a CAD model of the viewer, with one of the monitors and lenses removed for clarity.

Figure 2: a) porcine colon containing synthetic polyp and with circumferential ‘tattoo’ markings b) a participant with the simulated patient in lithotomy position.

Figure 3: Flowchart showing progress of recruits through the study

Stereoscopic vision tested

Participant randomly assigned an order of the 4 visual modalities (2D/3D/scope/box) in which to perform the tasks

Modality 1 e.g. 2D

3 x tasks performed

Modality 2 e.g. box

3x tasks performed

Modality 3 e.g. scope

3 x tasks performed

40 participants recruited and written consent gained

Modality 4 e.g. 3D

3 x tasks performed

Post-test questionnaires performed

Pre-test questionnaire completed

NASA-TLX completed

NASA-TLX completed

NASA-TLX completed

NASA-TLX completed

All pass test - no exclusions

Figure 4: Results of the post-test questionnaire on subjective opinion of different qualities of the four visual displays

Figure 5: Subgroup analysis of time taken by each group

Figure 6: Subgroup Analysis of path length

Figure 7: Subgroup analysis: accuracy (distance from cautery to target point to nearest 0.5mm)

Figure 8: subgroup analysis: Task Workload Index (as quantified by the NASA-TLX)