SOCIOECONOMICS AND HEALTH SERVICES
SECTION EDITOR: PAUL P. LEE, MD
Errors in Strabismus Surgery
Elizabeth Shen, BS; Travis Porco, PhD, MPH; Tina Rutar, MDObjectives:To determine the prevalence of and con-tributing factors for errors in strabismus surgery. Methods:Five hundred seventeen of 1103 strabismus surgeons (46.87%) completed a survey administered dur-ing the 2011 American Association for Pediatric Oph-thalmology and Strabismus national meeting or e-mailed to members of the association.
Results:One hundred seventy-three strabismus sur-geons (33.5%) self-reported having operated on the wrong eye or muscle or performed the wrong procedure at least once. The mean error rate was 1 in 2506 (95% CI, 2128-2941) operations. Surgeons who performed fewer than the median 1500 procedures had an error rate 5.9 (95% CI, 4.1-8.2) times higher than surgeons who performed
more than the median (P⬍.001). The most common
fac-tors contributing to errors were confusion between the type of deviation (esotropia/exotropia) and/or the
sur-gical procedure (recession/resection) (34 of 114 re-sponses [29.8%]), globe torsion (20 [17.5%]) leading pri-marily to inadvertent operation on the inferior rectus rather than the intended medial rectus muscle, and in-attention and/or distraction (19 [16.7%]). Running more
than 1 operating room (P= .02) and failing to mark eye
muscles preoperatively (P= .03) were associated with an
increased likelihood of error.
Conclusions:Self-reported error in strabismus surgery is a complication approximately as common as perior-bital cellulitis. Reducing error in strabismus surgery might entail confirming that the deviation matches the surgi-cal plan preoperatively, more elaborate site marking, and involving an assistant in a preoperative verification of the specific eye muscles and surgical procedure.
JAMA Ophthalmol. 2013;131(1):75-79
S
URGICAL ERRORS HAVE GAINEDincreasing attention in the media and medical litera-ture.1-7According to the Joint
Commission on Accredita-tion of Healthcare OrganizaAccredita-tions, wrong-site surgery is the most common error
causing patient injury.8A review of
ad-verse events within Veterans Health Ad-ministration hospitals found that ophthal-mology was second to neurosurgery as having the highest rates of surgical
er-rors.9Wrong intraocular lens (IOL)
im-plantation is the most common error in ophthalmic surgery, constituting 59% to 64% of errors.9-11
In 2004, the Joint Commission on Ac-creditation of Healthcare Organizations es-tablished the Universal Protocol to re-duce surgical errors. The protocol involves (1) systematic preoperative verification, in which relevant documents are reviewed for the correct patient, procedure, and site; (2) site marking; and (3) a “time-out” or suspension of activity to verify the spe-cific area and surgical procedure
imme-diately before incision.12The American
Academy of Ophthalmology has en-dorsed a preoperative checklist specific to
ophthalmology requiring verification of equipment to be used during each proce-dure (eg, the IOL) in addition to the
com-ponents of the Universal Protocol.13
Such protocols may be less effective in addressing error in strabismus surgery. Stra-bismus surgery can be performed on mul-tiple muscles in one or both eyes. Mark-ing the correct eye would not prevent a surgeon from operating on the incorrect muscle. The terms and abbreviations ET for esotropia, XT for exotropia, HT for hyper-tropia, HoT for hypohyper-tropia, rec for reces-sion, and res for resection can be easily mis-transcribed or confused. Because the surgical site is small, a nurse or an anes-thesiologist cannot easily verify that the muscle undergoing the operation is the in-tended muscle. The surgeon generally op-erates sitting at the patient’s head, creat-ing the potential for right/left and up/ down confusion.
We surveyed strabismus surgeons to es-timate the prevalence of errors in strabis-mus surgery and to assess factors that may have contributed to them. We used these data to suggest practices that might pre-vent strabismus surgery errors.
Author Aff Proctor Ins Ophthalmo Departmen (Drs Porco Epidemiolo (Dr Porco), (Dr Rutar), California, Ms Shen is University Francisco, Author Affiliations:Francis I.
Proctor Institute for Research in Ophthalmology (Dr Porco) and Departments of Ophthalmology (Drs Porco and Rutar), Epidemiology and Biostatistics (Dr Porco), and Pediatrics (Dr Rutar), University of California, San Francisco. Ms Shen is a medical student at University of California, San Francisco, School of Medicine.
METHODS
SURVEY ADMINISTRATION
We distributed a survey (eFigure; http://www.jamaophth .com) to strabismus surgeons during the American Associa-tion for Pediatric Ophthalmology and Strabismus 2011 na-tional meeting and via the association’s e-mail list. One thousand three surgeons had an opportunity to participate in the survey by completing it on paper at the national meeting from March 30 through April 3, 2011, or by completing it online (http:// www.surveymonkey.com) from April 29 through May 20, 2011. Survey participants were guaranteed anonymity. The study was approved by the institutional review board of the University of California, San Francisco.
DATA ANALYSIS
We defined an error in strabismus surgery as operating on the wrong eye or muscle or performing the wrong procedure for the patient’s underlying ocular deviation. The self-reported er-ror rate was calculated as the number of erer-rors divided by the number of lifetime strabismus operations reported by all sur-geons. We also calculated this rate for individual sursur-geons. We
compared the individual surgeon error rate between surgeons who had performed fewer than the median number of proce-dures (inexperienced surgeons) and those who had per-formed greater than the median (experienced surgeons) using the Wilcoxon rank sum test with continuity correction.
Errors were categorized as the wrong eye, the wrong extra-ocular muscle, the wrong procedure (such as resection in-stead of recession), or the wrong patient. For all errors that were adequately described by reporting surgeons, we classified con-tributing factors that may have led to the error.
We investigated whether the daily caseload or the running of multiple operating rooms might influence the likelihood of er-ror by performing a multivariate logistic regression in which we controlled for lifetime surgical volume. We used the Fisher ex-act test to compare error-prevention strategies between sur-geons who had experienced an error during their careers and those who had not. For all potential predictors of error in strabismus surgery found to be statistically significant (P⬍.05), we ex-plored whether the statistical significance withstood the Holm test of multiple comparisons.14Statistical analyses were performed using the R statistical package (http://www.r-project.org).
RESULTS
Surveys were completed by 517 of 1103 surgeons (211 during the American Association for Pediatric Ophthal-mology and Strabismus meeting and 306 online), for a response rate of 46.87%. One hundred seventy-three re-spondents (33.5%) reported an error made during their training or as an attending surgeon. Of the 152 sur-geons who reported having made an error as an attend-ing surgeon, 98 (64.5%) reported 1 error; 27 (17.8%), 2 errors; and 3 (2.0%), 3 errors during their careers. Twenty-four surgeons (15.8%) did not answer the question.
ERROR RATE
The error rate in strabismus surgery was 1 error for every 2506 (95% CI, 2128-2941) cases. The mean error rate for individual surgeons was 1 in 909 (95% CI, 714-1316) cases. The median error rate for individual surgeons was 1 in 2326 cases, with an upper quartile of 1 in 769 cases and a lower quartile of 1 in 4000 cases. The median number of re-ported strabismus procedures performed in a surgeon’s ca-reer was 1500. Inexperienced surgeons were 5.9 (95% CI, 4.1-8.2) times more likely to experience an error than ex-perienced surgeons (inexex-perienced surgeon error rate of 1 in 476 [357-714] cases vs experienced surgeon error rate
of 1 in 2778 [2439-3226] cases;P⬍.001).
TYPES OF ERRORS AND CONTRIBUTING FACTORS
The 173 errors consisted of 61 wrong procedures (35.3%), 38 wrong muscles (22.0%), 16 wrong eyes (9.2%), 4 wrong patients (2.3%), 11 miscellaneous (6.4%), and 43 unspeci-fied errors (24.9%). Of the 173 respondents, 114 de-scribed factors that may have contributed to the error. The most common contributing factors were confusion be-tween the type of deviation and/or surgical procedure (34 errors [29.8%]), globe torsion or anatomical difficulties (20 [17.5%]), and inattention and/or distraction (19
[16.7%]).Table 1describes the contributing factors by
Table 1. The Most Common Self-reported Contributing Factors Leading to Error in Strabismus Surgery
Factor No. (%) of Errorsa Wrong procedure (n = 54) Esotropia/exotropia or recession/resection confusion 34 (63) Hypertropia/hypotropia confusion 8 (15)
Inattention and/or distraction 6 (11)
Following preset pattern 5 (9)
Kestenbaum-Anderson confusionb 3 (6)
Wrong preoperative plan 3 (6)
Wrong muscle (n = 32)
Ocular torsion 20 (63)
Scarring, reoperation, or bleeding 8 (25)
Inattention and/or distraction 5 (16)
Wrong eye (n = 15)
No time-out 7 (44)
Lack of site marking or incorrect draping 4 (25)
Hypertropia/hypotropia confusion 4 (25)
Inattention and/or distraction 2 (13)
Wrong preoperative plan 2 (13)
Following preset patternc 2 (13)
Wrong patient (n = 4)
Wrong medical record consulted 2 (50)
Similar patient names 2 (50)
Change to surgical schedule resulting in a new order of patients
1 (25) Sequential patients with similar deviations; order
of patients confused
1 (25) Miscellaneous (n = 9)
Inattention and/or distraction 6 (67)
New assistant 3 (33)
Following preset pattern 2 (22)
aMore than 1 contributing factor could be attributed to each error case; thus, total percentages exceed 100.
bDefined as eye muscle surgical procedure performed in the direction opposite that needed to correct an anomalous head posture.
cIncludes repetition of a procedure performed previously on the same operative day; for example, a surgeon performs esotropia surgery on a fifth exotropic patient because the prior 4 patients had esotropia.
error subtype. Sixteen of the 114 respondents (14.0%) re-ported a combination of factors contributing to the error. The inferior rectus muscle was the most common “wrong muscle” (20 of 32 cases described in sufficient detail [62.5%]). In 16 of these cases, the surgeons described in-advertent inferior rectus surgery rather than intended me-dial rectus surgery.
Surgeons reported when the error was detected and corrected and who assisted in the case that resulted in surgical error. Results are shown in the eTable.
TIME-OUT
When asked if the surgeon had performed a time-out be-fore the case that resulted in an error, 86 (49.7%) of the 173 respondents reported not having performed a time-out, 53 (30.6%) did perform a time-out, and 34 (19.7%) did not answer the question. A time-out had been performed but failed to prevent an error in 22 (36.7%) of 60 wrong pro-cedures, 17 (48.6%) of 35 cases involving the wrong muscle, 4 (30.8%) of 13 involving the wrong eye, and 2 (50.0%) of 4 involving the wrong patient. Errors that could not be clas-sified were not counted in this calculation.
SURGICAL VOLUME
Most respondents (216 [45.8%]) performed 4 to 5 cases daily; few (13 [2.8%]) performed more than 10 cases daily. Twenty respondents (4.2%) ran 2 or more operating rooms simultaneously. In a multivariate analysis controlling for lifetime surgical volume, daily caseload was not a signifi-cant predictor of error (P= .13), but surgeons who ran mul-tiple operating rooms had a higher likelihood of reporting an error than surgeons who ran only 1 (P= .02;P= .06 af-ter correcting for multiple comparisons).
PREVENTIVE MEASURES
Table 2compares preventive practices of surgeons who reported and did not report errors. Only marking eye muscles before surgery was associated with a decreased likelihood of error (odds ratio, 0.63 [95% CI, 0.41-0.97];P= .03;P= .07 after correcting for multiple com-parisons).
COMMENT
PREVALENCE OF HUMAN ERROR IN STRABISMUS SURGERY
We anonymously surveyed 517 strabismus surgeons to estimate the prevalence of self-reported errors in stra-bismus surgery. One-third of strastra-bismus surgeons re-ported a surgical error during their careers, some as many as 3 times. In comparison, 21% of orthopedic hand
sur-geons had operated on the wrong site,15and 32% of
neu-rosurgeons had removed lumbar disc material from the
wrong spinal level.16We found an error rate of 4.0 per
10 000 strabismus procedures, which falls in the upper range of 0.09 to 4.5 per 10 000 cases for wrong-site sur-gery across all surgical fields.17We estimated the rates
of other complications of strabismus surgery from the lit-erature. The prevalence of scleral perforations is 30 to 280 per 10 000 strabismus cases18-23; periorbital/orbital
cellulitis, 5 per 10 000 cases24,25; and endophthalmitis, 0.05
per 10 000 cases.26,27Retinal detachment after
strabis-mus surgery has been described only in case reports.28,29
Thus, self-reported human error is less common than scleral perforation, is as common as periorbital/orbital cellulitis, and is more common than endophthalmitis and retinal detachment.
FACTORS CONTRIBUTING TO ERROR IN STRABISMUS SURGERY
We qualitatively and quantitatively studied factors lead-ing to error in strabismus surgery. Common contribut-ing factors included (1) confusion between recession and resection, esotropia and exotropia, and hypertropia and hypotropia; (2) globe torsion and anatomical difficul-ties; (3) inattention and/or distraction; (4) following a preset pattern (a surgeon who performs 5 esotropia re-pairs in a row inadvertently performs the same repair on the sixth exotropic case); (5) time-out omissions; (6) con-sulting the wrong medical record; (7) lack of site mark-ing and inappropriate drapmark-ing; (8) Kestenbaum-Anderson confusion (ie, an eye muscle surgical procedure performed in the direction opposite that needed to cor-rect an anomalous head posture); and (9) working with new assistants. Some surgeons described multiple fac-tors contributing to error (eg, 1 case involved visiting a regional hospital 950 miles away, late arrival to the op-erating room, an angry parent, an unskilled and upset surgical team, and no time-out).
Wrong procedures constituted the greatest propor-tion of error cases. Most of the wrong procedures were due to confusion of horizontal muscle recession and re-section and/or esotropia and exotropia (63%), which is
Table 2. Preventive Measures Taken to Reduce Likelihood of Error Preventive Measure No. (%) of Surgeonsa P Value Reporting Error (n = 143) Reporting No Error (n = 329) Examine patient preoperatively
on the same day as operation to confirm deviation
67 (46.9) 150 (45.6) .84
Mark the eye muscles and procedure to be performed on the patient’s face or on the drape
85 (59.4) 230 (69.9) .03
Discuss the surgical plan with an assistant surgeon
76 (53.1) 170 (51.7) .84 Post the preoperative
examination results where they are visible to the surgeon in the operating room
79 (55.2) 180 (54.7) .92
Post the surgical plan where it is visible during the operation
100 (69.9) 233 (70.8) .91
aSurgeons could select more than 1 preventive measure on the survey; thus, total percentages could exceed 100. Forty-five of 517 respondents did not answer the specific question.
not surprising because these terms represent the most common types of strabismus procedures. Confusion of recession and resection is not equally problematic; a re-cession can easily be converted to a resection, but an in-advertent resection converted to a recession may result in muscle tightening that limits ocular rotations.
Operating on the wrong muscle was the second most common error subtype (22.0%) and occurred most of-ten because of globe torsion (63%). Surgeons ofof-ten de-scribed haste and unrecognized globe rotation by the as-sistant as factors leading to inadvertent operations on the inferior rectus rather than the medial rectus muscle. Un-usual anatomy was a rare cause of operating on the wrong muscle. Patients may have torsional rotation of the or-bits and extraocular muscles that the surgeon does not recognize preoperatively, or they may have unusual lo-cations of the extraocular muscles owing to prior pro-cedures and scarring. Disinsertion of the incorrect muscle may disrupt the anterior-segment blood supply.
In our exploration of the effects of surgical experi-ence and surgical volume on error in strabismus sur-gery, we found that inexperienced surgeons had an er-ror rate 5.9 (95% CI, 4.1-8.2) times higher than
experienced surgeons (P⬍.001). Surgeons who
expe-rience an error early in their careers likely make changes to their surgical practices to prevent future errors. Per-forming a large number of cases each day was not asso-ciated with an increased likelihood of error, but
run-ning more than 1 operating room was (P= .02;P= .06
correcting for multiple comparisons).
PREVENTION OF HUMAN ERROR IN STRABISMUS SURGERY
We found that, in 53 of 139 surgical error cases (38.1%), a time-out had been performed but failed to prevent an error. The time-out, as commonly performed under the Universal Protocol, focuses on laterality and the type of procedure to be performed; for example, the surgeon might say, “Time-out, strabismus surgery, both eyes.” The time-out does not involve verification that a recession vs a resection is appropriate to treat the underlying devia-tion. Confusing recession and resection would be more devastating than operating on the wrong eye for a pa-tient undergoing a unilateral medial rectus resection and
lateral rectus recession for intermittent exotropia. Based on the quantitative and qualitative survey data analyses, we suggest that strabismus surgeons consider some modi-fications to the Universal Protocol (Figure).
Preoperative Verification
In addition to the standard preoperative verification, the surgeon should repeat an ocular alignment test to verify that the deviation matches that described in the medical record and confirm that the surgical plan correctly addresses the deviation. Although few surgeons operate with assistants knowledgeable in strabismus, when possible, an assistant should repeat these steps. The patient and caregivers should be involved in the preoperative verification process within the constraints of understanding strabismus.
Site Marking
We found that surgeons who marked eye muscles were less likely to experience error than those who did not
(P= .03;P= .07 after correcting for multiple
compari-sons). Because recession and resection and the abbre-viationsrecandrescan easily be mistranscribed and con-fused, using alternative terms may be more appropriate. We suggest that the surgeon place skin marks corre-sponding to the location of specific eye muscles rather than just marking the operative eye. The surgeon could
placeWfor weakening andSfor strengthening next to
these marks. Site markings should remain visible after
the patient is prepped and draped10and likely should be
placed after anesthesia induction for children who are fearful of marks being placed near the eyes.
Most errors involving wrong muscles were inadver-tent isolations of inferior rectus rather than medial rectus muscle. Thus, when performing medial rectus opera-tions, marking the nasal limbus with a dot can allow the surgeon and assistant to maintain appropriate orienta-tion before beginning manipulaorienta-tions that induce torsion.
Time-out
The strabismus surgery time-out should include the de-viation, the specific muscles to undergo operation, and the intended procedure (ie, “weakening both medial rec-tus muscles for esotropia” rather than “strabismus sur-gery, both eyes”). This recommendation is analogous to the American Academy of Ophthalmology Wrong-Site Task Force advocating the verification of IOL type and power—in addition to verifying the correct eye—to
ad-dress wrong IOL implantations.13The surgeon and staff
should recognize potential causes of error, including fol-lowing a preset pattern, distraction, a new assistant, run-ning multiple operating rooms, etc.
LIMITATIONS
Data were collected from an opt-in survey subject to se-lection bias of respondents. Reporting of errors, descrip-tions of errors, and lifetime surgical volume were sub-ject to recall bias. The self-reported surgical error rate could underestimate or overestimate the true rate. Al-Strabismus-specific modifications to the Universal Protocol
Preoperative verification
Verify that the preoperative ocular deviation matches the surgical plan
Site marking
Mark W or S next to the operative eye muscles, indicating weakening (recession) or strengthening (resection)
1. The preoperative deviation 2. The specific eye muscles
3. Whether weakening or strengthening will be performed
Time-out
Perform a time-out with the surgical assisant that includes:
Figure.Strabismus-specific modifications to the Universal Protocol to reduce surgical errors. We propose modifying the protocol to make it more likely to detect common sources of error in strabismus surgery.
though we ensured anonymity to survey respondents, con-cerns regarding professional reputation or liability may have led to underreporting of errors. Alternatively, sur-geons who had experienced error may have been more likely to participate owing to interest in the subject.
Most strabismus surgeons in the United States had the opportunity to participate in the survey, and we had a re-sponse rate of 46.87%. Because no mandatory or stan-dardized reporting of strabismus surgery errors exists, our survey data from 517 surgeons’ self-reports are currently the best available on this topic. Simon et al10analyzed data
from Ophthalmic Mutual Insurance Company malprac-tice claims and from the New York Patient Occurrence Re-porting and Tracking System and found only 1 strabis-mus case of 106 ophthalmic cases involving surgical confusion. Patients treated for strabismus often undergo reoperations. Thus, unlike lens exchanges, which are not expected after cataract surgery, reoperations for strabis-mus surgery errors could easily be underreported.
Our strabismus-specific modifications to the Univer-sal Protocol have not been prospectively evaluated as a means of reducing error. In the absence of mandated re-porting of errors and the relative rarity of such compli-cations, executing a prospective trial to evaluate a stra-bismus-specific Universal Protocol would be challenging. However, in a prospective trial involving 2 826 367 op-erations in 8 hospitals worldwide, Kwaan and
col-leagues4showed that implementing a specific checklist
for general surgery decreased mortality and surgical com-plications by 36%. Regimented adherence to protocols or checklists should not impair the surgeon’s flexibility in making intraoperative decisions. Rather, strabismus surgeons should adapt error-prevention strategies to their varied practice situations. Empowering assistants to par-ticipate in the preoperative verification and in the time-out and to verify correct muscle isolation and correct pro-cedure intraoperatively would take the onus off of the surgeon as the sole member of the surgical team respon-sible for these critical steps.30
In conclusion, our study found a self-reported error rate of 1 in 2506 strabismus cases. Most of the errors were confusion of recession and resection and of esotropia and exotropia. Site marking (ie, specific eye muscles, not just the eye) was associated with a decreased likelihood of error. Surgeon inexperience and running multiple oper-ating rooms were associated with an increased likeli-hood of error. Considering the results of this study, we suggest that strabismus surgeons consider modifying the Universal Protocol to address their subspecialty-specific causes of error better.
Submitted for Publication:February 9, 2012; final re-vision received May 26, 2012; accepted June 25, 2012.
Correspondence:Tina Rutar, MD, Department of Oph-thalmology, University of California, San Francisco, 10 Koret Way, K301, San Francisco, CA 94143 (rutart @vision.ucsf.edu).
Conflict of Interest Disclosures:The authors have no proprietary or commercial interest in any materials dis-cussed in this article.
Funding/Support:This study was supported by an un-restricted grant from Research to Prevent Blindness and
by institutional P30 core grant NEI EY002162-31 from the National Institutes of Health.
Online-Only Material:The eTable and eFigure are avail-able at http://www.jamaophth.com.
REFERENCES
1. A follow-up review of wrong site surgery.Jt Comm Perspect. 2002;22(1):10-11. 2. Catchpole K, Panesar S, Russell J, Tang V, Hibbert P, Cleary K.Surgical Safety Can Be Improved Through Better Understanding of Incidents.London, England: National Patient Safety Agency; 2009.
3. White MM, Gupta M, Utman SA, Dhillon B. Importance of side marking in oph-thalmic surgery.Surgeon. 2009;7(2):82-85.
4. Kwaan MR, Studdert DM, Zinner MJ, Gawande AA. Incidence, patterns, and pre-vention of wrong-site surgery.Arch Surg. 2006;141(4):353-358.
5. Clarke JR, Johnston J, Finley ED. Getting surgery right.Ann Surg. 2007;246(3): 395-405.
6. Clark S, Hamilton L. WHO surgical checklist: needs to be customised by specialty.
BMJ. 2010;340:c589. doi:10.1136/bmj.c589.
7. Ali N, Little BC. Causes of cataract surgery malpractice claims in England 1995-2008.
Br J Ophthalmol. 2011;95(4):490-492.
8. Joint Commission on Accreditation of Healthcare Organizations. Sentinel event statistics as of September 30, 2010. http://www.jointcommission.org/assets/1 /18/Stats_with_all_fields_hidden30September2010_(2).pdf. Accessed June 8, 2011.
9. Neily J, Mills PD, Eldridge N, et al. Incorrect surgical procedures within and out-side of the operating room.Arch Surg. 2009;144(11):1028-1034.
10. Simon JW, Ngo Y, Khan S, Strogatz D. Surgical confusions in ophthalmology.
Arch Ophthalmol. 2007;125(11):1515-1522.
11. Simon JW. Preventing surgical confusions in ophthalmology (an American Oph-thalmological Society thesis).Trans Am Ophthalmol Soc. December 2007; 105:513-529.
12. Joint Commission on Accreditation of Healthcare Organizations (JCAHO). JCAHO Universal Protocol for preventing wrong site, wrong procedure. 2003. http://www .jointcommission.org/standards_information/up.aspx. Accessed June 4, 2011. 13. American Academy of Ophthalmology. Patient safety: Recommendations of Ameri-can Academy of Ophthalmology Wrong-Site Task Force. http://one.aao.org/CE /PracticeGuidelines/Patient_Content.aspx?cid=d0db838c-2847-4535 -baca-aebab3011217. Accessed June 16, 2011.
14. Holm S. A simple sequentially rejective multiple test procedure.Scand J Stat. 1979;6(2):65-70.
15. Meinberg EG, Stern PJ. Incidence of wrong-site surgery among hand surgeons.
J Bone Joint Surg Am. 2003;85(2):193-197.
16. Jhawar BS, Mitsis D, Duggal N. Wrong-sided and wrong-level neurosurgery: a national survey.J Neurosurg Spine. 2007;7(5):467-472.
17. Devine J, Chutkan N, Norvell DC, Dettori JR. Avoiding wrong site surgery: a sys-tematic review.Spine (Phila Pa 1976). 2010;35(9)(suppl):S28-S36. doi:10.1097 /BRS.0b013e3181d833ac.
18. Surachatkumtonekul T, Phamonvaechavan P, Kumpanardsanyakorn S, Wong-pitoonpiya N, Nimmannit A. Scleral penetrations and perforations in strabismus surgery: incidence, risk factors and sequelae.J Med Assoc Thai. 2009;92(11): 1463-1469.
19. Dang Y, Racu C, Isenberg SJ. Scleral penetrations and perforations in strabis-mus surgery and associated risk factors.J AAPOS. 2004;8(4):325-331. 20. Noel LP. Retinal complications of strabismus surgery.Curr Opin Ophthalmol.
1998;9(3):56-58.
21. Park K, Hong S, Chung W, et al. Inadvertent scleral perforation after strabismus surgery: incidence and association with refractive error.Can J Ophthalmol. 2008; 43(6):669-672.
22. Taherian K, Sharma P, Prakash P, Azad R. Scleral perforations in strabismus sur-gery: incidence and role of prophylactic cryotherapy—a clinical and experimen-tal study.Strabismus. 2004;12(1):17-25.
23. Awad AH, Mullaney PB, Al-Hazmi A, et al. Recognized globe perforation during strabismus surgery: incidence, risk factors, and sequelae.J AAPOS. 2000; 4(3):150-153.
24. Kivlin JD, Wilson ME Jr; Periocular Infection Study Group. Periocular infection af-ter strabismus surgery.J Pediatr Ophthalmol Strabismus. 1995;32(1):42-49. 25. Ing MR. Infection following strabismus surgery.Ophthalmic Surg. 1991;22(1):
41-43.
26. Simon JW, Lininger LL, Scheraga JL. Recognized scleral perforation during eye muscle surgery: incidence and sequelae.J Pediatr Ophthalmol Strabismus. 1992; 29(5):273-275.
27. Recchia FM, Baumal CR, Sivalingam A, Kleiner R, Duker JS, Vrabec TR. Endoph-thalmitis after pediatric strabismus surgery.Arch Ophthalmol. 2000;118(7): 939-944.
28. Wolf E, Wagner RS, Zarbin MA. Anterior segment ischemia and retinal detachment after vertical rectus muscle surgery.Eur J Ophthalmol. 2000;10(1):82-87. 29. Casteels I, Gobin CV. Choroidal effusion with serous retinal detachment as a
com-plication of strabismus surgery [published online November 27, 2009].J Pedi-atr Ophthalmol Strabismus. doi:10.3928/01913913-20091118-02. 30. Sexton JB, Thomas EJ, Helmreich RL. Error, stress, and teamwork in medicine
