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Validation of a novel strabismus surgery 3D-printed silicone eye model for simulation training
Journal Pre-proof Validation of a novel strabismus surgery 3D-printed silicone eye model for simulation training Lisa Jagan, MD, Will Turk, MD, FRCSC, Christian Petropolis, MD, FRCSC, Rylan Egan, PhD, Nicholas Cofie, PhD, Kenneth W. Wright, MD, Yi Ning J. Strube, MD, FRCSC PII:
S1091-8531(20)30003-3
DOI:
https://doi.org/10.1016/j.jaapos.2019.10.008
Reference:
YMPA 3119
To appear in:
Journal of AAPOS
Received Date: 1 April 2019 Revised Date:
1 October 2019
Accepted Date: 20 October 2019
Please cite this article as: Jagan L, Turk W, Petropolis C, Egan R, Cofie N, Wright KW, Strube YNJ, Validation of a novel strabismus surgery 3D-printed silicone eye model for simulation training, Journal of AAPOS (2020), doi: https://doi.org/10.1016/j.jaapos.2019.10.008. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Copyright © 2020, American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.
Validation of a novel strabismus surgery 3D-printed silicone eye model for simulation training Lisa Jagan, MD,a Will Turk, MD, FRCSC,b Christian Petropolis, MD, FRCSC,c Rylan Egan, PhD,d Nicholas Cofie, PhD,d Kenneth W. Wright, MD,e and Yi Ning J. Strube, MD, FRCSCa Author affiliations: aDepartment of Ophthalmology, Queen’s University and Kingston Health Sciences Centre, Kingston, Ontario; bDepartment of Ophthalmology, University of Manitoba, Winnipeg, Manitoba; cDepartment of Surgery, Section of Plastic Surgery, University of Manitoba, Winnipeg, Manitoba; dOffice of Health Sciences Education, Faculty of Health Science, Queen’s University, Kingston, Ontario; eWright Foundation for Pediatric Ophthalmology and Strabismus, Los Angeles, California; Keck School of Medicine at University of Southern California, Los Angeles, California Financial support: grant funding from the Wright Foundation for Pediatric Ophthalmology and Strabismus, a not-for-profit 501(c)(3) foundation in Los Angeles. The sponsor or funding organization participated in conducting the study and reviewing the manuscript. US provisional patent pending (WT, CP) for silicone eye model: US 62/627, 853; Human Anatomic Model for Use in Surgical Simulation Having Synthetic Tissue Planes. Presented as a poster at the 122nd Annual Meeting of the American Academy of Ophthalmology, Chicago, Illinois, October 27-30, 2018. Submitted April 1, 2019. Revision accepted October 22, 2019. Corresponding Author: Yi Ning J. Strube, MD, MS, FRCSC, DABO, Department of Ophthalmology, Queen’s University, Hotel Dieu Hospital, 166 Brock Street, Kingston, Ontario, K7L 5G2, Canada (email: [email protected]). Word count: 2,991 Abstract only: 236
Abstract Purpose To demonstrate the validity of a new 3D-printed silicone model for practicing strabismus surgery, compared with the rabbit head, in terms of simulator fidelity. Methods In this multicenter study, a validated questionnaire was developed to assess fidelity of the model and rabbit head. Participants were asked to rate overall globe, conjunctiva, muscle, and scleral fidelity using a 5-point scale. The survey instrument was disseminated at three strabismus instruction courses: at two meetings, participants practiced on the model and rabbit head prior to completing the questionnaire; at the third, instructors demonstrated advanced surgical skills using only the model and then completed the questionnaire. Repeated measures analysis of variance compared ratings. Pearson’s or Spearman’s correlation evaluated correlation between years of experience to participants’ responses. Qualitative data were coded into themes. Results A total of 47 participants completed the questionnaire. The model rated 18% higher than rabbit head for anatomical accuracy (mean difference, 0.667; P = 0.001) and 25% higher for position of eyes within the head (mean difference, 0.867; P = 0.006). More experienced participants were more likely to strongly agree that the silicone conjunctiva effectively mimics real conjunctiva (ρ = 0.337; P = 0.036) and that scleral tissue effectively mimics real sclera (ρ = 0.298, P = 0.042). Qualitative data supported the model. Conclusions This study demonstrated the validity of the surgical model in terms of fidelity compared to the rabbit head.
Simulation-based training has become an integral part of surgical education. In ophthalmology, cataract surgery simulators have reduced intraoperative complications and accelerated resident learning.1-5 For strabismus surgery, however, ophthalmology residency programs still traditionally rely on operating room experience under the direct supervision of experienced mentors. This dependence on live experience is partly due to lack of appropriate simulators. There is minimal literature describing strabismus surgery simulation,6-12 yet simulation would be particularly valuable in this field, because opportunities for residents to refine their skills in the operating room are relatively limited compared, for example, to higher case volume cataract surgery. Strabismus surgery simulators include biologic and nonbiologic models. Biologic models include human cadaver, rabbit, pig, and cow eyes.9-12 These models are useful for simulating scleral needle passes, only one of many steps in strabismus surgery. Cadaver eyes vary in quality, often lack extraocular muscles and, as with animal eyes, require specialized facilities. Rabbit heads with eyes in situ allow for surgery on extraocular muscles within the orbit. It is the biologic system most similar to the human eye in terms of size and anatomy and is used by the authors in their strabismus surgical skills courses. Extraocular muscle substitutes for simulation have been described, including bacon,9 chicken breast,10 and, more recently, a multistep-assembly nonbiologic model12; although costefficient, they do not offer the same fidelity as silicone synthetic models. In the field of simulation, fidelity is defined as the degree to which a simulator looks and feels like a human patient. High-fidelity simulators are considered more realistic than low-fidelity simulators. To our knowledge, only two synthetic models (Phake-i, Eye Care and Cure, Tucson, AZ; Simulated Ocular Surgery model, Phillips Studio, Bristol, UK) are commercially available and have not
been validated in the literature with regard to fidelity. To target the limitations of available strabismus surgical simulators, 2 of the authors (CP, WT) designed a novel, cost-efficient, highfidelity 3D-printed silicone model. The purpose of this study was to compare the model to the rabbit head in terms of strabismus surgery simulator fidelity. Methods Queen’s University Health Sciences Research Ethics Board approval was obtained for this multicenter simulation fidelity study. Our research adhered to the tenets of the Declaration of Helsinki, and informed consent was obtained from all study participants. Silicone Model Design and Assembly The model is a proprietary design realized through 3D-printing technology. The anatomical references along with computed tomography and magnetic resonance imaging data were used to create 3D-representations of the globe, extraocular muscles, conjunctiva, cornea, and face. These components were assembled using silicone in a multiplanar fashion to ensure both anatomic fidelity and realistic tissue plane movement. Multiple iterations of the model prototype were rapidly produced in succession. Each subsequent prototype incorporated new design modifications to more accurately reflect tissue properties and surgical realism. The model requires minimal assembly. First, the eyes are attached to a silicone base (Figure 1A) using 4 tension bands, allowing the eye to rotate freely. The eye has both a conjunctival and scleral layer, between which lie 4 rectus muscles (Figure 1B). The base is covered with the silicone head so the eyes are appropriately aligned in the sockets (Figure 1C). Lubrication is used to allow fluid movements when sliding instruments along the conjunctiva, sclera, and muscle. The silicone head is reusable and does not require replacement with regular use. Each eye can be used for 4-8 practice muscle surgeries, depending on the surgeries being
performed. Rabbit Head Preparation Rabbit heads ordered from a local butcher were transported frozen and thawed prior to use and disposed of as biohazardous material after single use. They were pinned to a board laterally with the third eyelid and excess fur trimmed for globe exposure. A water-filled syringe allowed for eye inflation as needed. Pilot Project and Questionnaire Development A pilot project was undertaken at the 2017 annual meeting of the Canadian Ophthalmological Society, Strabismus Surgical Skills Transfer Course, held in Montreal. Participants practiced surgical skills on both the model and rabbit head (Figure 2) and voluntarily provided anonymous feedback regarding both models using a structured questionnaire. The promising results of the pilot data was the impetus to design a formal, validated questionnaire for this study. A modified Delphi technique was used to develop a validated questionnaire. A panel of 6 expert pediatric ophthalmologists provided feedback on the components of the pilot questionnaire. This feedback was obtained electronically using an online survey (Qualtrics, Provo, UT). Each pediatric ophthalmologist rated each statement on the questionnaire based on its effectiveness in assessing the fidelity of the models and provided free-text feedback regarding how the wording or content of the question could be changed in terms of wording or content. This process for obtaining expert feedback on the questionnaire was performed until 90% consensus was achieved. Validated Questionnaire The final validated questionnaire used for our study (see eSupplement 1, available at jaapos.org) collected demographic data and asked participants to rate both the model and the rabbit head
based on level of agreement with statements regarding the simulator’s fidelity. The agreement options included the following: 1 = strongly disagree, 2 = disagree, 3 = neutral, 4 = agree, and 5 = strongly agree. Statements were grouped into four categories describing overall globe, conjunctiva, muscle, and sclera fidelity. Participants could provide qualitative feedback using free text to describe their experiences using both models. Data Collection Data was obtained from three separate strabismus surgery skills transfer courses: (1) American Academy of Ophthalmology (AAO) Strabismus Surgery Skills Transfer Lab, New Orleans, Louisiana, November 12, 2017; (2) World Congress of Paediatric Ophthalmology and Strabismus (WCPOS) ORBIS-Sponsored Strabismus Surgery Breakfast Symposium, Hyderabad, India, December 2-3, 2017; and (3) the Wright Strabismus Surgery Course, Redondo Beach, California, January 20, 2018. The strabismus surgical techniques taught varied between courses and included rectus muscle plication, central tenotomy, central plication, nasal transposition of the lateral rectus muscle for oculomotor nerve palsy, and adjustable sutures. The validated questionnaire was disseminated, and data were collected using either an online or hardcopy survey. To avoid response bias of the participants with access to both the model and rabbit head, two versions of the hard copy survey were printed that varied the order of questions presented; participants were randomly given one version to complete. The designers of the model were not involved in data collection or analysis. Study Timeline and Course Details Participants in the AAO course had access to a rabbit head, model, and an operating microscope. A 1-hour didactic lecture preceded the 2-hour skills transfer course. Each participant practiced the surgical techniques on the rabbit head and the model (with randomization of order in which
participants were exposed to each system), with guidance from the instructors. Participants were invited to complete the hard copy questionnaire on course completion (n = 16 registered participants). The WCPOS course involved 8 international expert strabismus surgeons and was held on 2 separate days, with 4 experts instructing a total of 20 delegates each day. Each instructor taught a specific surgical technique of their choosing to a group of 4-5 delegates for 15 minutes, repeating 4 times in the 1-hour course. The instructor demonstrated the specific technique using only the model and surgical loupes; there were no rabbit heads for comparison. The instructors voluntarily completed the online questionnaire, which pertained to the model alone (n = 8 registered instructors). In the Wright Strabismus Surgery Course, each participant had access to a rabbit head, model, and surgical loupes. The course included a didactic lecture the day before the 2-hour skills transfer course. Equal numbers of tables were set up with either the rabbit head or model eye. Participants started the course at one table and switched tables midway during the course, allowing equal and randomized order of exposure to each system. Each participant practiced the surgical techniques on the rabbit head and the model with guidance from instructors. Participants were invited to complete the hard copy questionnaire on course completion (n = 39 registered participants). Statistical Analysis Questionnaire responses were analyzed using SPSS version 24 (IBM Corp, Armonk, NY). Repeated measures analysis of variance compared the rabbit and model ratings from the combined AAO and Wright courses, as participants had practiced on both the rabbit head and model. Spearman’s ρ correlation analysis was applied due to the violation of normality for the
variable “years of experience.” Pearson’s r parametric correlation analysis was performed when data from all three courses was combined for the model ratings alone. Qualitative data was coded and organized into themes. Results Combined demographic data from the 47 participants of the three courses who answered the questionnaire is summarized (Table 1). Average participation rate of instructors and course attendees to answer the questionnaire was 75% (Table 2). The participants were instructed to leave ratings blank if they did not use a given system, which allowed calculation of the percentage of participants that used either the rabbit head and/or the model. Combined Results Comparing the Model and Rabbit Head The model rated 18% higher than the rabbit head in terms of anatomical accuracy for strabismus surgery (mean difference [MD], 0.667; standard error [SE], 0.182; P = 0.001 [95% CI, 0.2951.038]). The model rated 25% higher than the rabbit head for the position and orientation of the eyes within the head (MD, 0.867; SE, 0.295; P = 0.006 [95% CI, 0.264-1.469]). The rabbit head rated 26% higher than the model for conjunctival tissue elasticity (MD, −0.767; SE, 0.266; P = 0.007 [95% CI, −1.310 to 0.223]). The model rated 13% higher than the rabbit for the “overall globe” grouping (MD, 0.467; SE, 0.219; P = 0.042 [95% CI, 0.019- 0.914]). The rabbit head rated 18% higher than the model for the “overall conjunctiva” grouping (MD, −0.550; SE, 0.234; P = 0.026 [95% CI, −1.028 to −0.720]). There was no statistically significant mean difference between the ratings of the model and rabbit head for all other statements/groupings of statements in the questionnaire (Figure 3). There was no statistically significant mean difference between the ratings of the model and rabbit head when the AAO course data was compared separately to the Wright course data.
The number of years in practice was plotted against the ratings of the model and rabbit head. The mean years of experience for pediatric ophthalmologists was 15.7 years; the combined mean years of experience for all other participants was 5.1 years. Therefore, participants with more years of experience were primarily seasoned pediatric ophthalmologists. More-experienced participants were more likely than less-experienced participants to strongly agree that the behavior and feel of the conjunctiva in the model effectively mimicked real conjunctiva (ρ = 0.337; P = 0.036). More-experienced participants were also more likely than less-experienced participants to strongly agree that the model scleral tissue effectively mimicked the resistance of real sclera when performing the scleral needle pass (ρ = 0.298; P = 0.042). More-experienced participants were less likely to strongly agree that the rabbit eye was anatomically accurate for strabismus surgery (ρ = −0.344; P = 0.046). Combined Results from AAO, Wright, and WCPOS Courses There was no statistically significant difference in the ratings of the model across the three courses. More-experienced participants were more likely to strongly agree that the model sclera effectively mimicked the resistance of real sclera for scleral passes (ρ = 0.298; P < 0.05). Qualitative Data Qualitative data was coded using Microsoft Excel (Microsoft Corporation, Redmond, WA) and grouped based on recurring themes. Table 3 summarizes all qualitative data from the courses. Discussion This study demonstrates the validity of a newly designed 3D-printed silicone model for strabismus surgery compared with the rabbit head in terms of simulation fidelity. Fidelity in this context refers to how well the model simulates live human surgery. Although the simulation literature suggests that low-fidelity models can be equally effective as high-fidelity models, this
usually applies to novice learners practicing simple technical skills.13-15 For the novice surgeon, even the lowest-fidelity simulator provides a useful learning experience; however, as the learner becomes more experienced and the surgical techniques become relatively more complex, a higher-fidelity simulator is likely to yield a more favorable experience. The intention of this study was to design and validate a high-fidelity model useful to a range of learners, from junior resident to experienced surgeon aiming to improve proficiency in new techniques. The model scored higher than the rabbit head for anatomical accuracy, position, and orientation of eyes within the globe, and overall globe ratings. Although the rabbit head scored higher than the model for conjunctival fidelity, participants with more years of experience rated the conjunctiva and sclera of the model more favorably than those with less experience. The qualitative data suggests that participants who had issues with the model’s conjunctiva found it to be too fragile under tension. It is possible that this was in part a reflection of surgical experience; that is, more-experienced surgeons handle tissue differently and therefore rated their experience with the tissue more favorably than did less-experienced surgeons. The qualitative data helped us understand participants’ experiences with both models, with the comments supporting the quantitative analysis. Although not formally assessed based on the study design, the qualitative data suggested that the model had advantages for teaching and learning, including, compared with the rabbit head, better exposure to demonstrate suture techniques. Strengths of this study include its use of the modified Delphi technique to validate the questionnaire.16 The consensus of pediatric ophthalmologists on the questionnaire limited significant gaps in content. Our study participation rate was very high (75%) and included a diverse group of international participants with varying expertise. The majority of participants
were pediatric ophthalmologists, an ideal population for a fidelity study because their experience with strabismus surgery makes them more attuned to the nuances of a simulator’s fidelity. The participant responses from the WCPOS course acted as a useful control, demonstrating the data’s robustness. At the WCPOS course, only instructors filled out the questionnaire, solely with access to the model. Despite this, their model scores were similar to the participants’ scores from the other courses, where participants used both the model and rabbit head. Even without a rabbit head comparator, the model was rated consistently across the three courses. The findings also indicate that a group of expert pediatric ophthalmologists at the WCPOS course perceived their experiences similarly to groups with more variable levels of expertise from the AAO and Wright courses, further supporting the value of this high-fidelity model for use by both novice and expert skill levels. Our sample size may be considered a study limitation; however, strabismus surgical skills courses are offered much less frequently than intraocular surgical skills courses due to costs, limited simulator availability, and the relatively lower volume of ophthalmologists performing strabismus surgery. This study was purposefully arranged based on the fortuity of three highquality, international courses occurring within a year, where two of the authors (YS, KW) were invited skills course directors. Therefore, the sample size can be considered reasonable in this context. Another limitation is that participants may have had more surgical attempts using one system than the other, and the number of attempts with each model was not recorded; nor did we record who started with which model and how this affected the responses. Limitations of the model include the lack of Tenon’s capsule, lack of oblique muscles, and the need for lubrication. The creators of this model are currently working to further optimize the model, including the
addition of oblique muscles, and refining the sclera and conjunctival tissue. Overall, this novel 3D-printed silicone model holds promise as a high-fidelity, costefficient simulator for strabismus surgery. Compared to biologic simulators, the silicone model obviates the need for biohazard precautions and disposal, and it is a reusable, clean, and ethical simulation platform that allows for ease of assembly and transportation outside of a formal wet lab for resident training. The ease of assembly, portability, and demonstrated fidelity of the model are useful qualities for use in remote areas and for varying levels of expertise. Future developments of the model are in progress for teaching more advanced oblique muscle surgeries. The model is being developed to limit costs to allow for greater accessibility and will be significantly cheaper than currently available noncadaveric models and cheaper than the costs of cadaveric rabbit heads. Ultimately, a simulator’s success depends on the fidelity of the simulator. However, it also depends on the curriculum that supports the simulator. Simulation is becoming a standard in medical education. It is important that in ophthalmology residency programs we prioritize simulation, including in strabismus surgery. Accordingly, we are currently developing an ophthalmology resident formal strabismus surgery curriculum using this model.
References 1.
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Roohipoor R, Yaseri M, Teymourpour A, Kloek C, Miller JB, Loewenstein JI. Early performance on an eye surgery simulator predicts subsequent resident surgical performance. J Surg Educ 2017;74:1105-15.
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Gertsch KR, Kitzmann A, Larson SA, et al. Description and validation of a structured simulation curriculum for strabismus surgery. J AAPOS 2015;19:3-5.
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McClatchey SK, Lane RG, Kubis KC, Boisvert C. Competency checklists for strabismus surgery and retinopathy of prematurity examination. J AAPOS 2012;16:75-9.
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Thomsen AS, Subhi Y, Kiilgaard JF, la Cour M, Konge L. Update on simulation-based surgical training and assessment in ophthalmology: a systematic review. Ophthalmology 2015;122:1111-30.e1.
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White CA, Wrzosek JA, Chesnutt DA, Enyedi LB, Cabrera MT. A novel method for
teaching key steps of strabismus surgery in the wet lab. J AAPOS 2015;19:468-70.e1. 10.
Fisher JB, Binenbaum G, Tapino P, Volpe NJ. Development and face and content validity of an eye surgical skills assessment test for ophthalmology residents. Ophthalmology 2006;113:2364-70.
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Vagge A, Gunton K, Schnall B. Impact of a strabismus surgery suture course for firstand second-year ophthalmology residents. J Pediatr Ophthalmol Strabismus 2017;54:33945.
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Adebayo T, Abendroth M, Elera GG, et al. Developing and validating a simple and costeffective strabismus surgery simulator. J AAPOS 2018;22:85-8.e2.
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Dunkin B, Adrales GL, Apelgren K, Mellinger JD. Surgical simulation: a current review. Surg Endosc 2007;21:357-66.
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Legends FIG 1. 3D-printed silicone model, requiring minimal assembly. A, The eyeballs are attached to a silicone base via four tension bands. B, There is a conjunctival layer (black arrowhead) covering the rectus muscles (asterisk) and the scleral layer (arrow). C, A silicone head faceplate covers the eyes for anatomically correct positioning of the eyeballs in socket. FIG 2. Muscle plication technique demonstrated on both models. A, Silicone model (earlier iteration). B, Rabbit head model. FIG 3. Combined results comparing the silicone model and rabbit head model (AAO and Wright courses). There were 13 statements pertaining to the silicone model and rabbit head (see questionnaire, page 2/3 [eSupplement 1]); only statistically significant differences are displayed in the graph. “Overall globe” refers to the combined ratings for the first three statements; “overall conjunctiva” refers to the combined ratings for the subsequent four statements on page 2 and 3 of the questionnaire.
a
Table 1. Combined demographic data of participants who answered questionnaire (N = 47) Variable Level of training Junior resident Senior resident Pediatric ophthalmology fellow Pediatric ophthalmologist General ophthalmologist Country or region of practice United States Canada Asia Europe Other Prior strabismus wet lab simulations 0 1 2 3 >3 Number of live strabismus surgeries performed 0 1 to 10 11 to 50 51 to 200 >200 Years in practice, mean (range) a
No. (%) 0 (0.0) 3 (6.4) 3 (6.4) 36 (76.6) 5 (10.6) 27 (57.4) 1 (2.1) 8 (17.0) 3 (6.4) 8 (17.0) 21 (44.7) 7 (14.9) 4 (8.5) 1 (2.1) 14 (29.8) 3 (6.4) 3 (6.4) 1 (2.1) 10 (21.3) 30 (63.8) 13.5 (0-51)
Participants of the three strabismus surgery instruction courses: AAO, Wright Strabismus Course, and WCPOS.
Table 2. Participant response rate to questionnaire Course Responses/total (%) AAO 2017 15/16 (94) WCPOS 2017 8/8 (100) Wright Strabismus 2018 24/39 (62) Total 47/63 (75)
Table 3. Summary of qualitative data from three separate strabismus skills courses Rabbit head Pros Cons Conjunctival tissue Messy, bloody, feels more realistic unpleasant smell (5) (24) Facilitates learning for Animal cruelty (4) oblique surgery (3)
Silicone model Pros Cons No obliques (8) Anatomically accurate (16)
Good exposure and orientation of muscles (14) Soft collapsible eyes Facilitates learning (13) plications and suture techniques (8) Small muscles, difficult Facilitates learning new exposure, harder to see surgical techniques (4) suture techniques (9) Reusable, clean (5)
a
a
Friable conjunctiva (10)
Cheese-wiring sclera (6)
Lubrication needed when hooking muscles; silicone can be sticky (4)
Numbers in parentheses represent the total number of individual comments of the specified theme. Repetitive comments from a single participant were considered a single comment.
S1091-8531(20)30003-3
DOI:
https://doi.org/10.1016/j.jaapos.2019.10.008
Reference:
YMPA 3119
To appear in:
Journal of AAPOS
Received Date: 1 April 2019 Revised Date:
1 October 2019
Accepted Date: 20 October 2019
Please cite this article as: Jagan L, Turk W, Petropolis C, Egan R, Cofie N, Wright KW, Strube YNJ, Validation of a novel strabismus surgery 3D-printed silicone eye model for simulation training, Journal of AAPOS (2020), doi: https://doi.org/10.1016/j.jaapos.2019.10.008. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Copyright © 2020, American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.
Validation of a novel strabismus surgery 3D-printed silicone eye model for simulation training Lisa Jagan, MD,a Will Turk, MD, FRCSC,b Christian Petropolis, MD, FRCSC,c Rylan Egan, PhD,d Nicholas Cofie, PhD,d Kenneth W. Wright, MD,e and Yi Ning J. Strube, MD, FRCSCa Author affiliations: aDepartment of Ophthalmology, Queen’s University and Kingston Health Sciences Centre, Kingston, Ontario; bDepartment of Ophthalmology, University of Manitoba, Winnipeg, Manitoba; cDepartment of Surgery, Section of Plastic Surgery, University of Manitoba, Winnipeg, Manitoba; dOffice of Health Sciences Education, Faculty of Health Science, Queen’s University, Kingston, Ontario; eWright Foundation for Pediatric Ophthalmology and Strabismus, Los Angeles, California; Keck School of Medicine at University of Southern California, Los Angeles, California Financial support: grant funding from the Wright Foundation for Pediatric Ophthalmology and Strabismus, a not-for-profit 501(c)(3) foundation in Los Angeles. The sponsor or funding organization participated in conducting the study and reviewing the manuscript. US provisional patent pending (WT, CP) for silicone eye model: US 62/627, 853; Human Anatomic Model for Use in Surgical Simulation Having Synthetic Tissue Planes. Presented as a poster at the 122nd Annual Meeting of the American Academy of Ophthalmology, Chicago, Illinois, October 27-30, 2018. Submitted April 1, 2019. Revision accepted October 22, 2019. Corresponding Author: Yi Ning J. Strube, MD, MS, FRCSC, DABO, Department of Ophthalmology, Queen’s University, Hotel Dieu Hospital, 166 Brock Street, Kingston, Ontario, K7L 5G2, Canada (email: [email protected]). Word count: 2,991 Abstract only: 236
Abstract Purpose To demonstrate the validity of a new 3D-printed silicone model for practicing strabismus surgery, compared with the rabbit head, in terms of simulator fidelity. Methods In this multicenter study, a validated questionnaire was developed to assess fidelity of the model and rabbit head. Participants were asked to rate overall globe, conjunctiva, muscle, and scleral fidelity using a 5-point scale. The survey instrument was disseminated at three strabismus instruction courses: at two meetings, participants practiced on the model and rabbit head prior to completing the questionnaire; at the third, instructors demonstrated advanced surgical skills using only the model and then completed the questionnaire. Repeated measures analysis of variance compared ratings. Pearson’s or Spearman’s correlation evaluated correlation between years of experience to participants’ responses. Qualitative data were coded into themes. Results A total of 47 participants completed the questionnaire. The model rated 18% higher than rabbit head for anatomical accuracy (mean difference, 0.667; P = 0.001) and 25% higher for position of eyes within the head (mean difference, 0.867; P = 0.006). More experienced participants were more likely to strongly agree that the silicone conjunctiva effectively mimics real conjunctiva (ρ = 0.337; P = 0.036) and that scleral tissue effectively mimics real sclera (ρ = 0.298, P = 0.042). Qualitative data supported the model. Conclusions This study demonstrated the validity of the surgical model in terms of fidelity compared to the rabbit head.
Simulation-based training has become an integral part of surgical education. In ophthalmology, cataract surgery simulators have reduced intraoperative complications and accelerated resident learning.1-5 For strabismus surgery, however, ophthalmology residency programs still traditionally rely on operating room experience under the direct supervision of experienced mentors. This dependence on live experience is partly due to lack of appropriate simulators. There is minimal literature describing strabismus surgery simulation,6-12 yet simulation would be particularly valuable in this field, because opportunities for residents to refine their skills in the operating room are relatively limited compared, for example, to higher case volume cataract surgery. Strabismus surgery simulators include biologic and nonbiologic models. Biologic models include human cadaver, rabbit, pig, and cow eyes.9-12 These models are useful for simulating scleral needle passes, only one of many steps in strabismus surgery. Cadaver eyes vary in quality, often lack extraocular muscles and, as with animal eyes, require specialized facilities. Rabbit heads with eyes in situ allow for surgery on extraocular muscles within the orbit. It is the biologic system most similar to the human eye in terms of size and anatomy and is used by the authors in their strabismus surgical skills courses. Extraocular muscle substitutes for simulation have been described, including bacon,9 chicken breast,10 and, more recently, a multistep-assembly nonbiologic model12; although costefficient, they do not offer the same fidelity as silicone synthetic models. In the field of simulation, fidelity is defined as the degree to which a simulator looks and feels like a human patient. High-fidelity simulators are considered more realistic than low-fidelity simulators. To our knowledge, only two synthetic models (Phake-i, Eye Care and Cure, Tucson, AZ; Simulated Ocular Surgery model, Phillips Studio, Bristol, UK) are commercially available and have not
been validated in the literature with regard to fidelity. To target the limitations of available strabismus surgical simulators, 2 of the authors (CP, WT) designed a novel, cost-efficient, highfidelity 3D-printed silicone model. The purpose of this study was to compare the model to the rabbit head in terms of strabismus surgery simulator fidelity. Methods Queen’s University Health Sciences Research Ethics Board approval was obtained for this multicenter simulation fidelity study. Our research adhered to the tenets of the Declaration of Helsinki, and informed consent was obtained from all study participants. Silicone Model Design and Assembly The model is a proprietary design realized through 3D-printing technology. The anatomical references along with computed tomography and magnetic resonance imaging data were used to create 3D-representations of the globe, extraocular muscles, conjunctiva, cornea, and face. These components were assembled using silicone in a multiplanar fashion to ensure both anatomic fidelity and realistic tissue plane movement. Multiple iterations of the model prototype were rapidly produced in succession. Each subsequent prototype incorporated new design modifications to more accurately reflect tissue properties and surgical realism. The model requires minimal assembly. First, the eyes are attached to a silicone base (Figure 1A) using 4 tension bands, allowing the eye to rotate freely. The eye has both a conjunctival and scleral layer, between which lie 4 rectus muscles (Figure 1B). The base is covered with the silicone head so the eyes are appropriately aligned in the sockets (Figure 1C). Lubrication is used to allow fluid movements when sliding instruments along the conjunctiva, sclera, and muscle. The silicone head is reusable and does not require replacement with regular use. Each eye can be used for 4-8 practice muscle surgeries, depending on the surgeries being
performed. Rabbit Head Preparation Rabbit heads ordered from a local butcher were transported frozen and thawed prior to use and disposed of as biohazardous material after single use. They were pinned to a board laterally with the third eyelid and excess fur trimmed for globe exposure. A water-filled syringe allowed for eye inflation as needed. Pilot Project and Questionnaire Development A pilot project was undertaken at the 2017 annual meeting of the Canadian Ophthalmological Society, Strabismus Surgical Skills Transfer Course, held in Montreal. Participants practiced surgical skills on both the model and rabbit head (Figure 2) and voluntarily provided anonymous feedback regarding both models using a structured questionnaire. The promising results of the pilot data was the impetus to design a formal, validated questionnaire for this study. A modified Delphi technique was used to develop a validated questionnaire. A panel of 6 expert pediatric ophthalmologists provided feedback on the components of the pilot questionnaire. This feedback was obtained electronically using an online survey (Qualtrics, Provo, UT). Each pediatric ophthalmologist rated each statement on the questionnaire based on its effectiveness in assessing the fidelity of the models and provided free-text feedback regarding how the wording or content of the question could be changed in terms of wording or content. This process for obtaining expert feedback on the questionnaire was performed until 90% consensus was achieved. Validated Questionnaire The final validated questionnaire used for our study (see eSupplement 1, available at jaapos.org) collected demographic data and asked participants to rate both the model and the rabbit head
based on level of agreement with statements regarding the simulator’s fidelity. The agreement options included the following: 1 = strongly disagree, 2 = disagree, 3 = neutral, 4 = agree, and 5 = strongly agree. Statements were grouped into four categories describing overall globe, conjunctiva, muscle, and sclera fidelity. Participants could provide qualitative feedback using free text to describe their experiences using both models. Data Collection Data was obtained from three separate strabismus surgery skills transfer courses: (1) American Academy of Ophthalmology (AAO) Strabismus Surgery Skills Transfer Lab, New Orleans, Louisiana, November 12, 2017; (2) World Congress of Paediatric Ophthalmology and Strabismus (WCPOS) ORBIS-Sponsored Strabismus Surgery Breakfast Symposium, Hyderabad, India, December 2-3, 2017; and (3) the Wright Strabismus Surgery Course, Redondo Beach, California, January 20, 2018. The strabismus surgical techniques taught varied between courses and included rectus muscle plication, central tenotomy, central plication, nasal transposition of the lateral rectus muscle for oculomotor nerve palsy, and adjustable sutures. The validated questionnaire was disseminated, and data were collected using either an online or hardcopy survey. To avoid response bias of the participants with access to both the model and rabbit head, two versions of the hard copy survey were printed that varied the order of questions presented; participants were randomly given one version to complete. The designers of the model were not involved in data collection or analysis. Study Timeline and Course Details Participants in the AAO course had access to a rabbit head, model, and an operating microscope. A 1-hour didactic lecture preceded the 2-hour skills transfer course. Each participant practiced the surgical techniques on the rabbit head and the model (with randomization of order in which
participants were exposed to each system), with guidance from the instructors. Participants were invited to complete the hard copy questionnaire on course completion (n = 16 registered participants). The WCPOS course involved 8 international expert strabismus surgeons and was held on 2 separate days, with 4 experts instructing a total of 20 delegates each day. Each instructor taught a specific surgical technique of their choosing to a group of 4-5 delegates for 15 minutes, repeating 4 times in the 1-hour course. The instructor demonstrated the specific technique using only the model and surgical loupes; there were no rabbit heads for comparison. The instructors voluntarily completed the online questionnaire, which pertained to the model alone (n = 8 registered instructors). In the Wright Strabismus Surgery Course, each participant had access to a rabbit head, model, and surgical loupes. The course included a didactic lecture the day before the 2-hour skills transfer course. Equal numbers of tables were set up with either the rabbit head or model eye. Participants started the course at one table and switched tables midway during the course, allowing equal and randomized order of exposure to each system. Each participant practiced the surgical techniques on the rabbit head and the model with guidance from instructors. Participants were invited to complete the hard copy questionnaire on course completion (n = 39 registered participants). Statistical Analysis Questionnaire responses were analyzed using SPSS version 24 (IBM Corp, Armonk, NY). Repeated measures analysis of variance compared the rabbit and model ratings from the combined AAO and Wright courses, as participants had practiced on both the rabbit head and model. Spearman’s ρ correlation analysis was applied due to the violation of normality for the
variable “years of experience.” Pearson’s r parametric correlation analysis was performed when data from all three courses was combined for the model ratings alone. Qualitative data was coded and organized into themes. Results Combined demographic data from the 47 participants of the three courses who answered the questionnaire is summarized (Table 1). Average participation rate of instructors and course attendees to answer the questionnaire was 75% (Table 2). The participants were instructed to leave ratings blank if they did not use a given system, which allowed calculation of the percentage of participants that used either the rabbit head and/or the model. Combined Results Comparing the Model and Rabbit Head The model rated 18% higher than the rabbit head in terms of anatomical accuracy for strabismus surgery (mean difference [MD], 0.667; standard error [SE], 0.182; P = 0.001 [95% CI, 0.2951.038]). The model rated 25% higher than the rabbit head for the position and orientation of the eyes within the head (MD, 0.867; SE, 0.295; P = 0.006 [95% CI, 0.264-1.469]). The rabbit head rated 26% higher than the model for conjunctival tissue elasticity (MD, −0.767; SE, 0.266; P = 0.007 [95% CI, −1.310 to 0.223]). The model rated 13% higher than the rabbit for the “overall globe” grouping (MD, 0.467; SE, 0.219; P = 0.042 [95% CI, 0.019- 0.914]). The rabbit head rated 18% higher than the model for the “overall conjunctiva” grouping (MD, −0.550; SE, 0.234; P = 0.026 [95% CI, −1.028 to −0.720]). There was no statistically significant mean difference between the ratings of the model and rabbit head for all other statements/groupings of statements in the questionnaire (Figure 3). There was no statistically significant mean difference between the ratings of the model and rabbit head when the AAO course data was compared separately to the Wright course data.
The number of years in practice was plotted against the ratings of the model and rabbit head. The mean years of experience for pediatric ophthalmologists was 15.7 years; the combined mean years of experience for all other participants was 5.1 years. Therefore, participants with more years of experience were primarily seasoned pediatric ophthalmologists. More-experienced participants were more likely than less-experienced participants to strongly agree that the behavior and feel of the conjunctiva in the model effectively mimicked real conjunctiva (ρ = 0.337; P = 0.036). More-experienced participants were also more likely than less-experienced participants to strongly agree that the model scleral tissue effectively mimicked the resistance of real sclera when performing the scleral needle pass (ρ = 0.298; P = 0.042). More-experienced participants were less likely to strongly agree that the rabbit eye was anatomically accurate for strabismus surgery (ρ = −0.344; P = 0.046). Combined Results from AAO, Wright, and WCPOS Courses There was no statistically significant difference in the ratings of the model across the three courses. More-experienced participants were more likely to strongly agree that the model sclera effectively mimicked the resistance of real sclera for scleral passes (ρ = 0.298; P < 0.05). Qualitative Data Qualitative data was coded using Microsoft Excel (Microsoft Corporation, Redmond, WA) and grouped based on recurring themes. Table 3 summarizes all qualitative data from the courses. Discussion This study demonstrates the validity of a newly designed 3D-printed silicone model for strabismus surgery compared with the rabbit head in terms of simulation fidelity. Fidelity in this context refers to how well the model simulates live human surgery. Although the simulation literature suggests that low-fidelity models can be equally effective as high-fidelity models, this
usually applies to novice learners practicing simple technical skills.13-15 For the novice surgeon, even the lowest-fidelity simulator provides a useful learning experience; however, as the learner becomes more experienced and the surgical techniques become relatively more complex, a higher-fidelity simulator is likely to yield a more favorable experience. The intention of this study was to design and validate a high-fidelity model useful to a range of learners, from junior resident to experienced surgeon aiming to improve proficiency in new techniques. The model scored higher than the rabbit head for anatomical accuracy, position, and orientation of eyes within the globe, and overall globe ratings. Although the rabbit head scored higher than the model for conjunctival fidelity, participants with more years of experience rated the conjunctiva and sclera of the model more favorably than those with less experience. The qualitative data suggests that participants who had issues with the model’s conjunctiva found it to be too fragile under tension. It is possible that this was in part a reflection of surgical experience; that is, more-experienced surgeons handle tissue differently and therefore rated their experience with the tissue more favorably than did less-experienced surgeons. The qualitative data helped us understand participants’ experiences with both models, with the comments supporting the quantitative analysis. Although not formally assessed based on the study design, the qualitative data suggested that the model had advantages for teaching and learning, including, compared with the rabbit head, better exposure to demonstrate suture techniques. Strengths of this study include its use of the modified Delphi technique to validate the questionnaire.16 The consensus of pediatric ophthalmologists on the questionnaire limited significant gaps in content. Our study participation rate was very high (75%) and included a diverse group of international participants with varying expertise. The majority of participants
were pediatric ophthalmologists, an ideal population for a fidelity study because their experience with strabismus surgery makes them more attuned to the nuances of a simulator’s fidelity. The participant responses from the WCPOS course acted as a useful control, demonstrating the data’s robustness. At the WCPOS course, only instructors filled out the questionnaire, solely with access to the model. Despite this, their model scores were similar to the participants’ scores from the other courses, where participants used both the model and rabbit head. Even without a rabbit head comparator, the model was rated consistently across the three courses. The findings also indicate that a group of expert pediatric ophthalmologists at the WCPOS course perceived their experiences similarly to groups with more variable levels of expertise from the AAO and Wright courses, further supporting the value of this high-fidelity model for use by both novice and expert skill levels. Our sample size may be considered a study limitation; however, strabismus surgical skills courses are offered much less frequently than intraocular surgical skills courses due to costs, limited simulator availability, and the relatively lower volume of ophthalmologists performing strabismus surgery. This study was purposefully arranged based on the fortuity of three highquality, international courses occurring within a year, where two of the authors (YS, KW) were invited skills course directors. Therefore, the sample size can be considered reasonable in this context. Another limitation is that participants may have had more surgical attempts using one system than the other, and the number of attempts with each model was not recorded; nor did we record who started with which model and how this affected the responses. Limitations of the model include the lack of Tenon’s capsule, lack of oblique muscles, and the need for lubrication. The creators of this model are currently working to further optimize the model, including the
addition of oblique muscles, and refining the sclera and conjunctival tissue. Overall, this novel 3D-printed silicone model holds promise as a high-fidelity, costefficient simulator for strabismus surgery. Compared to biologic simulators, the silicone model obviates the need for biohazard precautions and disposal, and it is a reusable, clean, and ethical simulation platform that allows for ease of assembly and transportation outside of a formal wet lab for resident training. The ease of assembly, portability, and demonstrated fidelity of the model are useful qualities for use in remote areas and for varying levels of expertise. Future developments of the model are in progress for teaching more advanced oblique muscle surgeries. The model is being developed to limit costs to allow for greater accessibility and will be significantly cheaper than currently available noncadaveric models and cheaper than the costs of cadaveric rabbit heads. Ultimately, a simulator’s success depends on the fidelity of the simulator. However, it also depends on the curriculum that supports the simulator. Simulation is becoming a standard in medical education. It is important that in ophthalmology residency programs we prioritize simulation, including in strabismus surgery. Accordingly, we are currently developing an ophthalmology resident formal strabismus surgery curriculum using this model.
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Legends FIG 1. 3D-printed silicone model, requiring minimal assembly. A, The eyeballs are attached to a silicone base via four tension bands. B, There is a conjunctival layer (black arrowhead) covering the rectus muscles (asterisk) and the scleral layer (arrow). C, A silicone head faceplate covers the eyes for anatomically correct positioning of the eyeballs in socket. FIG 2. Muscle plication technique demonstrated on both models. A, Silicone model (earlier iteration). B, Rabbit head model. FIG 3. Combined results comparing the silicone model and rabbit head model (AAO and Wright courses). There were 13 statements pertaining to the silicone model and rabbit head (see questionnaire, page 2/3 [eSupplement 1]); only statistically significant differences are displayed in the graph. “Overall globe” refers to the combined ratings for the first three statements; “overall conjunctiva” refers to the combined ratings for the subsequent four statements on page 2 and 3 of the questionnaire.
a
Table 1. Combined demographic data of participants who answered questionnaire (N = 47) Variable Level of training Junior resident Senior resident Pediatric ophthalmology fellow Pediatric ophthalmologist General ophthalmologist Country or region of practice United States Canada Asia Europe Other Prior strabismus wet lab simulations 0 1 2 3 >3 Number of live strabismus surgeries performed 0 1 to 10 11 to 50 51 to 200 >200 Years in practice, mean (range) a
No. (%) 0 (0.0) 3 (6.4) 3 (6.4) 36 (76.6) 5 (10.6) 27 (57.4) 1 (2.1) 8 (17.0) 3 (6.4) 8 (17.0) 21 (44.7) 7 (14.9) 4 (8.5) 1 (2.1) 14 (29.8) 3 (6.4) 3 (6.4) 1 (2.1) 10 (21.3) 30 (63.8) 13.5 (0-51)
Participants of the three strabismus surgery instruction courses: AAO, Wright Strabismus Course, and WCPOS.
Table 2. Participant response rate to questionnaire Course Responses/total (%) AAO 2017 15/16 (94) WCPOS 2017 8/8 (100) Wright Strabismus 2018 24/39 (62) Total 47/63 (75)
Table 3. Summary of qualitative data from three separate strabismus skills courses Rabbit head Pros Cons Conjunctival tissue Messy, bloody, feels more realistic unpleasant smell (5) (24) Facilitates learning for Animal cruelty (4) oblique surgery (3)
Silicone model Pros Cons No obliques (8) Anatomically accurate (16)
Good exposure and orientation of muscles (14) Soft collapsible eyes Facilitates learning (13) plications and suture techniques (8) Small muscles, difficult Facilitates learning new exposure, harder to see surgical techniques (4) suture techniques (9) Reusable, clean (5)
a
a
Friable conjunctiva (10)
Cheese-wiring sclera (6)
Lubrication needed when hooking muscles; silicone can be sticky (4)
Numbers in parentheses represent the total number of individual comments of the specified theme. Repetitive comments from a single participant were considered a single comment.