Surgical complications have been defined by Sokol

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1 Severe complications of strabismus surgery John A. Bradbury, MBChB, FRCOphth, a and Robert H. Taylor, MBBS, FRCOphth b PURPOSE METHODS RESULTS CONCLUSIONS To determine the type, incidence, and clinical outcomes of severe complications from strabismus surgery in the United Kingdom. Cases were identified prospectively through a national surveillance unit between September 1, 2008, and August 31, Questionnaire data were requested at the time of the complication recognition and at 6 months follow-up. Outcome was graded I to V, with a poor or very poor outcome meaning either loss of corrected visual acuity or primary position double vision. A total of 60 completed reports of adverse events and complications were received during the study period. During the same time approximately 24,000 strabismus surgeries were performed in the United Kingdom, yielding an overall incidence of 1 in 400 operations (95% binomial confidence, 1 per operations). The most common reported complication was perforation of the globe (19 [0.08%]), followed by a suspected slipped muscle (16 [0.067%]), severe infection (14 [0.06%]), scleritis (6 [0.02%]), and lost muscle (5 [0.02%]). Overall, complications were reported in adults and children in equal numbers; however, scleritis was significantly more common in adults. A poor or very poor clinical outcome was recorded as 1 operation per 2,400. This study provides an assessment of the overall risks associated with strabismus surgery in the United Kingdom. Complications with the potential for a poor outcome are relatively common, but the final clinical outcome is good in the majority of cases. ( J AAPOS 2013; 17:59-63) Surgical complications have been defined by Sokol and Wilson 1 as any undesirable, unintended, and direct result of an operation affecting the patient, which would not have occurred had the operation gone as well as could reasonably be hoped. This definition could be expanded to include an unexpected result. Complications can be self-limiting or severe. Severe complications of strabismus are defined here as potentially associated with a poor outcome, for example, reduced visual acuity or intractable double vision. The range of complications and their sequelae is large; for example, an inadvertent perforation is usually of little significance but can lead to loss of the eye. A suspected slipped muscle may require further surgical exploration on the part of the surgeon, only to find the muscle securely attached where the original surgeon intended. Author affiliations: a Bradford Royal Infirmary, Bradford, United Kingdom; b York Hospital, York, United Kingdom Financial support: National Eye Research (Yorkshire). National Eye Research played no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript. Submitted June 2, Revision accepted October 13, Published online January 25, Correspondence: John A. Bradbury, MBChB, FRCOphth, Eye Department, Bradford Royal Infirmary, Duckworth Lane, Bradford, BD9 6RJ, United Kingdom ( John. Bradbury@bthft.nhs.uk). Copyright Ó 2013 by the American Association for Pediatric Ophthalmology and Strabismus /$ Studies on complications of strabismus surgery have usually concentrated on one type of incident, such as ocular perforation, 2 orbital infection, 3 or slipped and lost muscles. 4 Some complications, such as scleritis, have only been reported as a single case 5 or small case series. 6 The definitions of some of these complications vary, 2,7 as do the incidence rates of, for example, globe perforation (from 0.13% of operations 5 to 7.8% of eyes operated 2 ) and orbital infections (from 1: to 1: ). The authors have found no data on the incidence of lost muscle or surgically induced necrotizing scleritis. Although in many publications authors report clinical outcomes, 9,10 it is difficult to glean an overall incidence rate. The purpose of this study is to determine the incidence of severe complications of strabismus surgery and to outline their clinical outcomes. Methods Multicenter ethical committee approval was granted for this study. A 2-year prospective study into severe complications of strabismus surgery was conducted based on data from the British Ophthalmic Surveillance Unit (BOSU). The methodology has been used before in many studies through BOSU, an active surveillance system. 11 All consultant and associate specialist ophthalmologists in the United Kingdom are surveyed monthly by BOSU concerning up to 10 rare eye conditions of interest that are currently being tracked. The recipient list 59

2 60 Bradbury and Taylor Volume 17 Number 1 / February 2013 Table 1. Complications studied a Complication Globe perforation Suspected slipped muscle Orbital infection Intraoperative lost muscle Endophthalmitis Retinal detachment Definitions to include A breach of the scleral wall into the suprachoroidal space or beyond Scleral pass that intuitively feels has passed into the suprachoroidal space Presentation of choroidal pigment Presentation of vitreous Intraocular hemorrhage Unexpected misalignment with duction deficit in the action of the suspected slipped muscle, with or without double vision. Postoperative inflammation of the orbital tissues beyond expected (2 days to 3 months). Whole muscle, including capsule, is uncontrolled during strabismus surgery Muscle may or may not be found again. Excludes longitudinal split Vitreous cells postoperatively (1 day to 3 months) Separation of neurosensory retina (1 day to 3 months) SINS, surgically induced necrotizing scleritis. a Scleritis and SINS were not defined on the original literature; however, questionnaires were returned to the authors reporting scleritis and as associated with a poor outcome, in some cases, are included. is maintained by BOSU, who monitor and conduct an annual telephone census of new appointments. If the consultant has treated one of the conditions within the previous month, this is communicated to BOSU, which informs the principle investigator (J.A.B.), who sends the consultant a questionnaire to document the case; a follow-up questionnaire is sent 6 months later to record the outcome or, in some cases, persistent symptoms and signs (for the original and follow-up questionnaires, see e-supplement 1, available at jaapos.org). From September 1, 2008, to August 31, 2010, the card included severe complications of strabismus surgery. The complications studied and definitions used are provided in Table 1. In addition to the 7 target complications, cases of scleritis and surgically induced necrotizing scleritis were reported because surgeons were asked to report any serious postoperative complication. To reflect common practice, complications have been classified as sight-threatening (globe perforation, infection, scleritis) and ocular motility-related, causing duction deficits and/or double vision (slipped muscle, lost muscle). The clinical outcomes of the complications were classified as defined in Table 2. This classification was conceived by the primary author (J.A.B.) for the present study. To calculate risk, the total number of strabismus operations performed annually in the United Kingdom was ascertained from the Hospital Episode Statistics database 12 of the Information Centre for Health and Social Care. The data are derived from health care episodes, including surgical procedures, in the National Health Service in England. In (the latest year published) 11,209 strabismus surgeries were reported. To estimate the total operation rate of the United Kingdom, as opposed to England alone, we rounded this figure up to 12,000. To corroborate this figure, we surveyed surgeons in the North East of England performing strabismus surgery for the period September 9, 2009, to November 30, In this population of approximately 8.5 million, a total of 513 procedures were on 964 muscles. Scaling this up for the entire United Kingdom would yield a rate of approximately 14,000 operations per annum. By using 12,000, we believed that any error would calculate a slight overestimation of the complication rate, which we thought would be safer than an underestimation. Table 2. Classification of clinical outcome at 6 months Type Characteristics I No intervention a required: good outcome II Surgical or medical intervention: asymptomatic b ; good outcome III Surgical or medical intervention: asymptomatic; outcome compromised c IV Surgical or medical intervention: poor outcome Reduced corrected visual acuity (up to 2 lines loss on Snellen chart) and/or Double vision in the primary position, treated with prisms, or double vision in some gaze positions or distance, requiring treatment (eg, partial occlusion or prisms in reading glasses) V Surgical or medical intervention: very poor outcome Reduced corrected visual acuity of $2 lines of loss on Snellen chart Intractable double vision a Intervention included any procedure, modification of a procedure, or medical treatment that would not have occurred without the complication. It excluded further examinations (such as retinal examination) that may have occurred in the case of a suspected complication. b Asymptomatic was used to describe the absence of symptoms that could be construed to be secondary to the complication. c Compromised was defined as not requiring specific treatment but double vision present only in eccentric gaze, a duction deficit, or a primary position deviation of.10 D from aimed. The patient with some retinal traction near a perforation entry site but with no visual sequelae was also included in this category. Results There were 40 replies in the first year and 20 in the second year. On the basis of our calculation of 12,000 strabismus surgeries per annum, yielding an incidence of primary complications of 1 in 300 after the first year (95% CI, 1 per operations) and 1 per 400 operations (95% CI one per operations) for both years. Sightthreatening complications occurred in 1.6 per 1,000 operations; motility-related complications, 0.9 per 1,000 operations. Demographic characteristics of the patient cohort with complications are provided in Table 3. Secondary complications occurred in 10% of the 60 patients

3 Volume 17 Number 1 / February 2013 Bradbury and Taylor 61 Table 3. Characteristics of population reported with complications Number of patients Criteria (frequency) Type of primary surgery Esotropia 30 of 60 (50%) Exotropia 25 of 60 (40%) Other Preoperative refraction $ of 60 (10%): 2 SO weakness, 1 nystagmus surgery, 1 thyroid 7 of 45 (15%) myopia ( D) Reoperations 22 of 60 (36.7%) Age groups All patients (mean age, 12.2 yrs) 60 Children a (mean age, 6.7 yrs) 28 Adults (mean age, 45.1 yrs) 32 Adjustable planned Adults (n 5 32) 14 (43%) Children (n 5 28) 3 (9.7%) Intraocular muscle Medial rectus Lateral rectus Superior rectus Superior oblique Inferior rectus Suture material Polyglactin of 57 (98%) Nylon 1 of 57 (2%) Secondary complication 24 of 51 (41%): 58% OS 20 of 51 (20%): 45% OS 3 of 51 (5%): 2 OD, 1 OS 2 of 51 (3%): bilateral case 2 of 51 (3%): both OU Laterality Right eye 27 of 60 Left eye 31 of 60 Bilateral 2 of 60 Surgeon position Head 38 of 59 (64%) Side 20 of 59 (34%) Both 1 of 59 (2%) Surgeon hand dominance Right 53 of 58 (91%) Left 5 of 58 (9%) 6 of 60 (10%): 3 slipped muscle, 1 RD, 1 IR weakness, 1 endophthalmitis D, diopters; IR, inferior rectus muscle; OD, right eye; OS, left eye; OU, both eyes; RD, retinal detachment; SO, superior oblique muscle. a Defined as \16 years of age at the time of surgery. Table 4A. Clinical outcomes of all complications reported in adults a Classification type b Complication I II III IV V Total Perforation Slipped muscle Infection Scleritis Lost muscle Retinal detachment 1 1 Endophthalmitis 0 Table 4B. Clinical outcomes of all complications reported in children Classification type b Complication I II III IV V Total Perforation Slipped muscle Infection Scleritis 0 Lost muscle 0 Retinal detachment 0 Endophthalmitis 1 1 a Inferior rectus weakness is not included. Note, patients with multiple complications are counted more than once. b Classification types are defined in Table 2. after globe perforation (1 retinal detachment, 1 endophthalmitis), infection (3 suspected slipped muscles), and scleritis (1 inferior rectus weakness). The clinical outcomes of all primary and secondary complications are provided in Table 4. Surgically induced scleritis was significantly more common in adults (P ). No other statistical significance between adults and children was found. Of the 60 patients, 10 (4 adults, 6 children) had a poor or very poor outcome (grade IV or V), yielding an overall rate of 0.04%, or 1 in 2,400 patients, for all strabismus procedures. Of the 19 cases of globe perforation (0.08% of all strabismus surgeries), 17 were recognized at the time of the surgery, with 1 patient presenting on day 17 with a field defect secondary to a choroidal hemorrhage and 1 case presenting with a corneal abscess (Streptococcus pneumoniae) and perforation 10 days after surgery. In 3 cases the anterior chamber was perforated during placement of a traction suture; in 1 of these, the procedure was subsequently abandoned because of a soft eye, and in 1 case an anterior chamber wash-out was performed and the perforation repaired. There was a nearly equal distribution of laterality, where information was provided (8 right, 9 left), and 1 perforation was bilateral (during bilateral superior oblique surgery on a patient with high myopia). Surgery was being performed on the medial rectus muscle (6 patients), lateral rectus muscle (9 patients), superior rectus muscle (1 patient), and superior oblique muscle (1 bilateral patient). All surgeons but one were right-handed, and all but one sat at the head of the table. Dilated fundus examination was performed during the strabismus surgery in 12 patients, and postoperatively in 3 more, in response to the suspected perforating injury. In the 4 remaining cases no retinal examination was reported. A perioperative vitreoretinal opinion was available in 5 cases (and was obtained subsequently in the 3 cases). Retinal treatment was as follows: no treatment (7 patients), cryotherapy (3 patients), diode laser (2 patients), and cryotherapy and gas (1 patient). All retinal treatments were performed at the time of strabismus surgery, with 1 exception (diode laser carried out for a retinal detachment 5 days postoperatively). The 1 patient with a choroidal hemorrhage resolved without any long-term sequelae. One child presented with a corneal abscess, infiltrating the limbus, after suspected corneal perforation. The presentation was 10 days after surgery and Streptococcus pneumoniae was isolated. Intensive topical and systemic antibiotics were

4 62 Bradbury and Taylor Volume 17 Number 1 / February 2013 commenced. A conjuctival flap was used to preserve the globe and the patient referred to a second center, where no further treatment was recommended. The child presented with prolapsed ocular contents 6 weeks after surgery. After discussion with the parents, an evisceration was performed to prevent sympathetic ophthalmia. Postoperative antibiotics were prescribed systemically in 2 patients (in one patient, intravenous ciprofloxacin per operatively followed by oral administration). Overall the outcome was good, although in 3 adults this was compromised (1 patient with retinal traction and 2 patients with duction deficits). One of these was the myopic patient who had bilateral perforations, during Harado Ito procedures and retinal laser in one eye. There were 16 cases (0.07%) of suspected slipped muscle. All muscles were initially sutured with 6-0 polyglactin 910 sutures. The medial rectus slipped in 8 cases, the lateral rectus in 6, and the inferior rectus in 2. Of the 7 adults, 5 had an adjustable suture. All had subsequent surgery to correct the resultant overcorrection (with the exception of the 1 perioperative slip). The reasons given for a slipped muscle included hang-back snapped, suture cheese wired or cut out at scleral bite (2 patients), adjustable slipped (1 patient), muscle found further back than intended (3 patients), slipped muscle found at correct location (3 patients) and pseudotendon (4 patients). These last 4 presented at 9, 42, 53, and 104 days after surgery. The outcome in adults after surgical revision was very good but compromised in children, with 2 having a compromised outcome (grade III), 1 having a duction deficit, 1 having poor alignment, and 3 with persistent double vision (grade IV). There were 14 patients with orbital infection (0.06%), 9 presenting with symptoms and signs characteristic of cellulitis (pain, swelling, redness) of the periorbita/muscles (Table 5). Information on medication, where provided, consisted of intravenous antibiotics in 4 cases, oral antibiotics in 5, and systemic antibiotic in 1 (route unspecified). Further procedures were performed on 6 patients for excision of suture granuloma (2 patients), 3 who had a suspected slipped muscle, and 1 of whom had subconjunctival antibiotics. Two children had persistent symptoms of inflammation, with 1 report of inflammation, double vision, and poor appearance at 6 months (graded IV). One further case had intermittent double vision following a secondary slipped muscle (graded IV). There were 6 adults (no children) reported with scleritis (0.02%). Information on systemic conditions was not requested. Information is available on treatment in 5 cases, which included cyclophosphamide, intravenous methylprednisolone, oral and topical steroids, and oral nonsteroidal anti-inflammatory drugs. One patient, who presented with an irritable eye 14 days after surgery, had a scleral melt and required a conjunctival autograft nearly 2 years later with a good visual outcome. Six months postoperatively, 2 further patients were waiting for cataract surgery. One of these had a reduction of vision to 6/24 from 6/6 (grade V) and the other to a level of 6/18 from 6/12 (grade IV). Table 5. Frequency of primary complications Complication a Total number (adults:children b ), percentage of all strabismus surgery Mean time between surgery and presentation, days (range) Globe perforation b 19 (7:12), 0.08 N/A (0-17) Slipped muscle 16 (7:9), (0-104) Infection 14 (3:11), (1-65) Scleritis/SINS 6 (6:0), (7-34) Intraoperative lost muscle 5 (5:0), 0.02 N/A N/A, not available; SINS, surgically induced necrotizing scleritis. a Secondary complications (not included) occurred after globe perforation (1 retinal detachment, 1 endophthalmitis), infection (3 suspected slipped muscles), and scleritis (1 inferior rectus weakness). b Defined as \16 years of age at the time of surgery. There were 5 cases, all adults, of lost muscle (0.02%), 4 of which involved the medial rectus muscle and one the lateral rectus muscle. Reasons provided included muscle snapped over hook (2 medial, 1 lateral rectus), sutures cut too short at adjustment, and muscle split while placing sutures. Of these 5 cases, 4 were reoperations; the muscle was found in all 4. In the fifth patient, the medial rectus muscle was found but snapped a second time on attempted reattachment and not relocated. This patient had a stay suture through the inferior and superior rectus to hold the eye in adduction for 6 weeks. In this case the patient ended up with an overcorrection of 18 D but still had a 1 adduction deficit. There was a poor outcome in 1 patient (grade IV), who required prism to control double vision and 3 patients who graded III because of duction deficits. Discussion To our knowledge, this is the first prospective multicenter, multicomplication study of severe complications of strabismus surgery. The overall complication rate is similar for adults and children; however, some complications, such as scleritis, are more common in adults. Lost muscle also was more common in adults (but not statistically significant), possibly in association with repeated operations, particularly on the medial rectus muscle. Infections were more common in children (but not statistically significant), also reported by Kivlin and Wilson. 3 We agree that this is likely due to fingers reaching the eyes in the postoperative period or coexistent sinus disease. The greater incidence of perforation in children may be related to surgical access (although this again was not statistically significant). Dang and colleagues 2 make a distinction between ocular perforation (defined as a breach in the scleral wall) and penetration (where a retinal hole is observed). Our reported rate of ocular perforation (including penetration) is much lower than that of Dang s prospective study (7.8%) and more in line with 1.42%. 13 In our study the outcome was generally good; however, 1 case had an extremely unusual postoperative course resulting in evisceration. In 2 other cases perforation occurred into the anterior chamber in association with the placement of traction sutures. This

5 Volume 17 Number 1 / February 2013 Bradbury and Taylor 63 complication was higher than expected. Another prospective study 13 suggested that treatment of retinal holes might not be required, based on an animal model. A further study recommended prophylactic laser. 14 Parks and Bloom 15 used the term slipped muscle to describe a muscle attached via its capsule. The term pseudotendon is often used (rightly or wrongly) to describe what could be a slipped muscle or stretched scar. 16 In 3 cases of our cases, the muscle was found at reoperation to be where it had been reattached, suggesting simply an exaggerated response to surgery (for whatever reason). We recorded these cases as slipped because they fit our predefined definition. The frequency of orbital infections (0.07%) was slightly less than that reported by Kivlin and Wilson. 3 Two cases were reported with suspected suture granulomas: correspondence confirmed the coexistence of bacterial contamination in one of these. In addition, 3 cases of infection subsequently developed slipped muscles, all of which required further surgery to reattach the muscle; these cases suggest that infection may alter the healing process and lead to poor muscle adherence. In our study, scleritis occurred only in adults, and we believe this is the first study to highlight this complication as significant (0.025%); however, information on pre-existing conditions that might predispose patients to scleritis, such as systemic autoimmune conditions and ischemia, was not collected. We included snapped muscle in the lost muscle group, although this has been defined as a separate entity. 17 The medial rectus muscle was the most common lost muscle, as previously reported. 18 We found that the loss was often the result of a snapped muscle in adults who were undergoing repeat surgery. Relatively poor outcome was common (grade III or IV) due to poor alignment and duction deficits, despite the surgeon finding the lost muscle in 4 of 5 cases. The present study has several limitations. The questionnaire design led to limited clinical information on individual cases: however, we were seeking to report an overall percentage of severe complications and their clinical outcome. A second limitation is that we do not know the denominator in many of the subcategories that may predispose to complications (for example, reoperations, number of surgeries operated by trainees). We attempted to define the complications in line with previous publications. The complication rate may suffer from underreporting; for example, there was a decrease in patient reports in the second year, which may represent loss of interest in the study. Finally, the lack of statistical significance in some of our results may be due to the small numbers in each subgroup, which weakens any subsection analysis. In conclusion, the overall complication rate of severe complications is 1 in 400 operations of all patients operated on, with 16% of these experiencing a poor or very poor outcome (approximately 1 in 2,400). This is approximately the same for both adults and children, although the complications differ for each age group. We acknowledge that the study design might have led to underreporting and that small numbers in each category are not sufficient to provide firm recommendations. Literature Search PubMed and MEDLINE were searched for Englishlanguage results with unrestricted dates using strabismus complication(s) and associated terms: infection, slipped muscle, lost muscle, globe perforation, scleritis, retinal detachment. Acknowledgments The authors thank Andy Scally for help with the statistical calculations and Barny Foot (BOSU) for help and guidance with the questionnaire construction. References 1. Sokol DE, Wilson J. What is a surgical complication? World J Surg 2008;32: Dang Y, Racu C, Isenberg SJ. Scleral penetrations and perforations in strabismus surgery and associated risk factors. J AAPOS 2004;8: Kivlin JD, Wilson ME. The periocular infection study group. Periocular infection after strabismus surgery. J Pediatr Ophthalmol Strabismus 1995;32: Cherfan CG, Traboulsi El. Slipped, severed, torn and lost extraocular muscles. Can J Ophthalmol 2011;46: Kearney FM, Blaikie AJ, Gloe GA. Anterior necrotizing scleritis after strabismus surgery in a child. J AAPOS 2007;11: Sykes SO, Riemann C, Santos CI, et al. Haemophilus influenzae associated scleritis. Br J Ophthalmol 1999;83: Awad AH, Mullaney PB, Al-Hazmi A, et al. Recognized globe perforation during strabismus surgery: Incidence, risk factors and sequelae. JAAPOS 2000;4: Ing MR. Infection following strabismus surgery. Ophthalmic Surg 1991;22: Walton RC, Cohen AS. Staphylococcus epidermidis endophthalmitis following strabismus surgery. J AAPOS 2004;8: Recchia FM, Baumal CR, Sivalinham A, Kleiner R, Duker JS, Vrabec TR. Endophthalmitis after pediatric strabismus surgery. Arch Ophthalmol 2000;118: Foot BG, Stanford MR, Rahi J, Thompson JR. The British ophthalmological surveillance unit: An evaluation of the first 3 years. Eye 2003;17: Department of Health: HES online. Total procedures and interventions. siteid51937&categoryid5210. Updated Accessed May Taherian K, Sharma P, Prakash P, Azad R. Scleral perforation in strabismus surgery: Incidence and role of prophylactic cryotherapy a clinical and experimental study. Strabismus 2004;12: Sprunger DT, Klapper SR, Bonnin JM, Minturn JT. Management of experimental globe perforation during strabismus surgery. J Pediatr Ophthalmol Strabismus 1996;33: Parks MM, Bloom JN. The slipped muscle. Ophthalmology 1979; 86: Ludwig I. Scar remodeling after strabismus surgery. Trans Am Ophthalmol Soc 1999;47: MacEwen CJ, Lee JP, Fells P. Aetiology and management of the detached rectus muscle. Br J Ophthalmol 1992;76: Lenart TD, Lambert SR. Slipped and lost extraocular muscles. Ophthalmol Clin North Am 2001;14: