AR Projections for Eye-gaze Evaluation in Phantoms
Phase: NA
Conditions: Kidney Stones
Sponsor: Vanderbilt University Medical Center

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
  
  
  
  
  
  
  
Development and Validation of a Gaze-based Training for Endoscopic Kidney Stone Surgery 
  
Nicholas Kavoussi md 
Assistant Professor of Urologic Surgery 
Vanderbilt University Medical Center 
Department of Urologic Surgery 
6/11/24 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
  
Table of Contents: 
  
Study Schema 
1.0          Background 
2.0          Rationale and Specific Aims 
3.0          Animal Studies and Previous Human Studies 
4.0          Inclusion/Exclusion Criteria 
5.0          Enrollment/Randomization 
6.0          Study Procedures 
7.0          Risks of Investigational Agents/Devices (side effects) 
8.0          Reporting of Adverse Events or Unanticipated Problems involving Risk to  
   Participants or Others 
9.0          Study Withdrawal/Discontinuation 
10.0       Privacy/Confidentiality Issues 
11.0       Follow-up and Record Retention 
12.0       Funding 
  
 
 

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
 
1.0          Background 
This project aims to develop an augmented reality (AR) tool to enhance skill 
acquisition for endoscopic kidney stone surgery. Of the 100,000 patients who 
undergo an endoscopic kidney stone treatment annually in the United 
States, 25% will require a repeat stone surgery within 20 months of their index 
surgery [1, 2, 3, 4]. The repeat stone surgery rate is almost completely driven by 
postoperative residual stone fragments, which lead to ureteral obstruction 
causing pain, urinary tract infection, and kidney injury [5, 6, 7]. One significant 
factor that contributes to residual stone fragments is limited visualization of the 
entire collecting system - a skill directly associated with surgeon experience [8]. 
This leads to novice surgeons having a much higher recurrence rate than 
experienced ones. As the incidence of kidney stone disease continues to 
increase (prevalence of 10%, incidence of 1116 per 100,000), improved 
endoscopic surgical training is required to improve outcomes of stone surgeries 
and minimize complications by improving stone-free rate [9, 4]. 
Currently, skill assessment during endoscopic stone surgery is limited. There are 
no objective metrics for endoscopic surgery to assess skill. The only feedback 
trainees get is in the form of verbal communication from expert surgeons, usually 
after the conclusion of surgery. Thus, most feedback is synoptic and limited in 
facilitating skill acquisition [10]. Operative time and patient safety concerns 
restrict the amount of active, real-time feedback given during a case for skill 
acquisition. Endoscopic kidney stone surgery is uniquely challenging given the 
small depth and field of view of current endoscopes, which complicate the 
complete visualization of the entire collecting system. Navigation of the collecting 
system relies on mentally mapping preoperative imaging to the endoscopic 
surgical field. Success in mapping relies on hand-eye coordination, memory, and 
spatial reasoning, which are gained through practice. Thus, there is a need for 
tools that facilitate endoscopic surgical skill acquisition. 
The overarching hypothesis for this research is that we can improve surgical skill 
acquisition and outcomes for endoscopic kidney stone surgery by integrating eye 
gaze sharing during procedures. Eye gaze guidance has been shown to lead to 
better skill acquisition in virtual reality surgical tasks compared with motion 
guidance alone [11]. The proposed system would provide real-time education for 
trainees during endoscopic stone surgery such as through head-mounted 
displays (i.e., the Microsoft Hololens 2). We have previously demonstrated eye 
gaze sharing in phantoms. By implementing this system in the operating room 
(OR), we would be able to instill durable skill acquisition in trainees. 
2.0          Rationale and Specific Aims 

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
The aims of this study are to: 
1. Evaluate skill level during endoscopic stone surgery using optical tracking. 
2. Evaluate skill acquisition during endoscopic stone surgery using optical 
tracking. 
3.0          Animal Studies and Previous Human Studies 
We have previously demonstrated an eye tracking method during endoscopic 
kidney stone surgery using the Microsoft HoloLens 2 (Microsoft Corporation, 
Redmond, WA) [27]. Our method of eye tracking is independent of head motion 
or surgeon movement. We evaluated the method in a task-directed study in 
phantoms, comparing six trainees and four expert surgeons. Surgeons are 
categorized as expert (fellowship-trained endourologist, average case volume of 
> 100 ureteroscopy per year) or trainees (< 100 ureteroscopy per year). 
Specifically, we asked each participant to localize fiducial kidney stones in three 
phantoms. We evaluated and compared eye tracking metrics between experts 
and trainees. We found statistically significant differences in multiple parameters, 
including gaze path, fixation number and time, and gaze area. Specifically, expert 
surgeons completed the task in 52s compared to 318 s for trainees (p < 0.01), 
experts’ gaze traveled 7.32 m during that time compared to 19.92 m for trainees 
(p < 0.01), and the total area covered by experts’ gaze was 1045 cm2 compared 
to 1433 cm2 for trainees (p < 0.01). This suggests that experienced surgeons 
have more deliberate eye movements overall when exploring surgical anatomy, 
while trainees have to visually examine more of the displayed anatomy to 
complete a task (Fig. 1).  
 
Fig 1: Trace of gaze over an entire stone identification trial for trainee and expert overlaid on a screenshot. Trainees’ 
gaze explores a much larger area whereas experts’ gaze is more focused. 

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
4.0          Inclusion/Exclusion Criteria 
For expert surgeons 
Exclusion Criteria 
 
1. If the expert surgeon does not wish to participate. 
Inclusion criteria 
1. Any board-certified urologist who would like to participate 
 
 
For residents 
Exclusion Criteria 
1. Medical students, fellows or other non-urologic residents 
2. Urology residents who wish to not participate 
Inclusion Criteria 
1. Any urology resident 
For Patients 
Exclusion Criteria 
1.Pediatric patients (<18 years old). 
2. Anatomy or medical history that precludes ureteroscopy 
3. Kidney stones >2cm in the longest diameter 
Inclusion Criteria 
1.Patients who are candidates for kidney stone surgery with ureteroscopy 
 
5.0          Enrollment 
We will identify all urology residents who are undergoing surgical training at 
VUMC. All residents will perform perioperative and operative duties as per 
standard of care and training at our facility as determined by the American College 
of Graduate Medical Education (ACGME). The identified resident information will 
be shared with investigators using standard secure file transfer according to 
protocol. Expert surgeons will be identified as any board certified urology faculty 
at VUMC. Identifying information (name, DOB, etc) will be saved in encrypted, 

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
password protected files. We plan on enrolling 10 residents in this initial study for 
evaluation of the technology and workflow. Patients undergoing ureteroscopy will 
be informed of the study.  
6.0          Study Procedures 
We will recruit ten urology residents who will prospectively be randomized into 
the control and experimental groups and measure their performance 
intraoperatively during stone localization. Specifically, each trainee will be tasked 
with stone localization as is standard of care during ten endoscopic stone surgery 
under the guidance of an expert surgeon. Ten expert surgeons will also be 
recruited. All trainees and experts will wear HoloLens 2s to track their eye gaze. 
The trainees and experts in the control group’s HoloLenses will not show any 
augmentation, but trainees in the control group will receive verbal feedback from 
an expert surgeon as is standard procedure. In the experimental group, the 
trainees’ HoloLenses will project the experts eye gaze (in the form of a virtual 
pointer) in addition to verbal feedback from the expert surgeon. Each trainee will 
perform stone localization in six separate patients with either solely verbal 
(control group) or verbal and gaze guidance to test skill acquisition (expert 
group). Then, the trainees will perform stone identification in four additional 
patients without guidance. After localization, the remainder of the case will 
continue as is standard of care. After the first six patients, each trainee in both 
groups will perform the same visualization task on four new patients with only 
verbal guidance. Quantitative metrics: We will measure the total percentage eye 
gaze area seen during all ten surgeries to assess skill acquisition. Additionally, 
we will measure if there is a significant difference between the performance of 
each group in the last four surgeries. We will also evaluate differences in the 
NASA Task Load Index for the surgeons. Statistical Evaluation and Sample Size: 
A t-test will evaluate the hypothesis that surgeons eye gaze area decreases with 
exposure to the eye gaze sharing system. With an estimated average of 70% 
decrease, each surgeon must complete 10 cases to measure a 15% 
improvement in gaze area with a statistical significance of 0.05 and a power of 
0.8. 
7.0          Risks of Investigational Agents/Devices 
As the surgery itself will proceed as standard of care, there is little risk residents. 
The greatest risk would be a privacy breach which will be mitigated by securely 
storing identifying information and promptly destroying it once it is no longer 

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
needed. There are no foreseen risks to patients as surgery is to proceed as is 
standard of care. No patient data will be recorded. 
8.0          Reporting of Adverse Events or Unanticipated Problems involving 
Risk to Participants or Others 
No adverse events are anticipated. However, unanticipated problems will be 
reported to the IRB by the PI within 5 business days of the discovery. 
9.0          Study Withdrawal/Discontinuation 
Subjects will be withdrawn from the study if access is unobtainable in a 
retrograde fashion. Subjects may withdraw from the study at any time. 
10.0         Privacy/Confidentiality Issues 
Data will be collected and stored within REDCap (Research Electronic Data 
Capture). Only key study personal listed as the principal investigator, study 
coordinator research- clinical roles and REDCap data manager will have access 
to the research information. The investigator and study coordinator at each site 
will have access to the medical record numbers and unique study identification 
numbers for each of their participants. Only the study coordinator and research-
clinical roles will have access to the surgeon survey responses; the principal 
investigator and those listed as sub-investigators will not have access to this data 
prior to data analysis. Eye gaze data will be de- identified when stored in an 
encrypted drive and will be accessible only by key study personnel. Consent 
forms will be obtained per REB requirements and will be secured in a password 
protected-electronic study binder or paper study binder, stored in a locked office. 
Responses to surgeon questionnaires will be collected via REDCap. At the 
completion of the study, study data will be downloaded from REDCap to be 
stored on the study binder. 
11.0         Follow-up and Record Retention 
It is anticipated the data collection will take 12 months to complete, and another 
12 months to analyze the data.  All identifiers will be destroyed 4 years after the 
study initiation, or 2 years after data collection is complete, whichever is sooner.  
12.0         Funding 
National Institute of Health 1R211EB035783 (pending review): Development and 
Validation of Gaze-based Training for Endoscopic Kidney Stone Surgery 

Vanderbilt University Medical Center  
Department of Urologic Surgery  
A-1302 Medical Center North  
Nashville, TN 37232-2765 
 
 
 
 
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