Abstract
A total of 167 cases (0.111%) of infectious complications (endophthalmitis, orbital cellulitis, preseptal cellulitis, and postoperative infection) were identified in patients after strabismus surgery. The incidence of postoperative endophthalmitis was approximately 1 per 13,700 strabismus surgeries (0.007%) among 151,011 strabismus surgeries in US claims databases.
Infections following strabismus surgery include subconjunctival abscess, sub-Tenon’s abscess, periorbital and orbital cellulitis, and endophthalmitis. Mild periocular infections can be treated with antibiotics with no long-term sequelae; however, severe periocular or intraocular infections, including orbital cellulitis and endophthalmitis, can result in vision loss.
Several studies have reported the incidence of infectious complications following strabismus surgery; however, two of these studies were based on surveys of strabismus surgeons and did not provide an exact denominator, and a third study was limited to data from a single institution.1–3 We conducted this study to determine the incidence of infectious complications following strabismus surgery using commercial insurance claims data.
Subject and Methods
This research is covered under Stanford Population Health Sciences (PHS) protocol 40974. This population-based retrospective cohort study was performed using claims data that were analyzed separately from the Optum SES Medical Claims dataset from Optum’s De-identified Clinformatics Data Mart (CDM, 2003–2020) and MarketScan Research Databases (IBM, 2007–2016). The CDM database is a deidentified commercial and Medicare Advantage claims database. The dataset comprises patient claims information on approximately 15–18 million annually covered lives, for a total of over 63 million lives from a geographically diverse population spanning all 50 states of the United States. The Optum dataset from CDM provides demographic and medical claims data for inpatient and outpatient services, including surgery. The MarketScan Databases comprises more than 240 million patients insured by 350 unique health carriers. These data include health insurance claims across the continuum of care as well as enrollment data from large employers and health plans across the United States. Data access for this project was provided by the Stanford Center for Population Health Science Data Core.
Patients in either database who had undergone strabismus surgery constituted the denominator for the purposes of calculating postoperative infection rates. Only patients who had International Classification of Disease (ICD) codes for infectious complications (endophthalmitis, orbital cellulitis, preseptal cellulitis and postoperative infection) between the date of strabismus surgery and 1 month postoperatively were defined as cases of postoperative infection. To ensure the accuracy of the diagnosis of postoperative endophthalmitis, data analysis included only patients who had a claim submitted for intravitreal aspiration, intravitreal injection, or vitrectomy within 2 weeks of the diagnosis of endophthalmitis (eSupplement 1, available at jaapos.org). For patients with more than one strabismus surgery occurring during the enrollment period, all subsequent surgeries after the first surgery were considered reoperations. The add-on Current Procedural Terminology (CPT) code (67332), which implies previous surgery involving the extraocular muscles, was used to identify cases in which the first strabismus surgery occurring during the enrollment period was itself a reoperation. We assessed sex, age, surgical methods, reoperation, and the period between the day of strabismus surgery and diagnosis of infectious complications in both databases, separately.
Results
A total of 7,601,339,218 claims for 66,228,965 patients were analyzed using the Optum SES Medical Claims dataset (version 4.0), and a total of 8,713,134,185 claims for 123,637,720 patients were analyzed in the MarketScan Databases (version 2.0). Among 55,516 strabismus surgeries, 67 patients had infectious complications following strabismus surgery in the Optum dataset. In the MarketScan Databases, among 95,495 strabismus surgeries, 100 patients had infectious complications postoperatively (0.111%, 167/151,011). The median age was 7.0 years (Q1-Q3, 3.0–30.0), and 78 patients (46.7%) were female. The median interval between strabismus surgery and the diagnosis of infectious complications was 6.0 days (Q1-Q3, 4.0–12.5). Children (age <13years) accounted for 111 cases (66.5%). Of all strabismus surgery cases, 67.9% (102,539/151,011) were children, with a postoperative infectious complication rate of 0.108% (111/102,539) among children. Overall, fifty-three cases (31.7%) had postoperative infectious complications after reoperation. The percentage of reoperation among all strabismus surgery cases was 29.8% (44,963/151,011), with a postoperative infectious complication rate of 0.118% (53/44,963). In cases of primary strabismus surgery, the postoperative infectious complication rate was 0.107% (114/106,048). The number of patients with postoperative infections who underwent only horizontal or vertical muscle surgeries was 133 (79.7%), and the number of patients who underwent combined vertical and horizontal muscle surgery was 34 (20.4%). The postoperative infectious complication rate was 0.108% (133/123,337) in cases with only horizontal or vertical muscle surgeries and 0.123% (34/27,674) in cases with combined vertical and horizontal muscle surgery.
Endophthalmitis occurred in 11 (0.007%) patients and the median age of these patients was 46.0 (Q1-Q3, 16.5–58.0) years (Table 1). The median interval between strabismus surgery and the diagnosis of endophthalmitis was 10.0 (Q1-Q3 5.0–13.5) days.
Table 1.
Demographics and characteristics of patients with infectious complications following strabismus surgery
| Patient characteristic | Total patients (n = 167) | Infectious complication rates (%) |
|---|---|---|
| Sex, n (%) | ||
| Female | 78 (46.7) | |
| Male | 89 (53.3) | |
| Age, yearsa | 7.0 [3.0;30.0]a | |
| Surgical methods, no. (%) | ||
| Horizontal or vertical muscle surgery | 133 (79.6) | |
| Combined vertical and horizontal muscle surgery | 34 (20.4) | |
| Reoperation, no. (%) | 53 (31.7) | |
| Infectious complications, no. (%) | 0.111 | |
| Endophthalmitis | 11 (6.6) | 0.007 |
| Orbital cellulitis | 60 (35.9) | 0.040 |
| Preseptal cellulitis | 68 (40.7) | 0.045 |
| Postoperative infection | 28 (16.8) | 0.019 |
| Time between strabismus surgery and diagnosis of infectious complication, days | 6.0 [4.0;12.5]a |
Median value [quartile 1; quartile 3].
Discussion
Periocular and orbital infections are rare after strabismus surgery, but they can be sight-threatening. The Periocular Infection Study Group reported 25 cases of cellulitis and 3 cases of subconjunctival abscess in a survey of 308 AAPOS members.4 Infectious complications occurred predominantly in preschool patients. Another study that surveyed 63 strabismus surgeons reported an incidence of orbital cellulitis of 1 per 1,900 cases (0.052%).1 A prospective study in the United Kingdom reported that of approximately 24,000 patients who underwent strabismus surgery, 0.06% developed an orbital infection, and 1 patient developed endophthalmitis.2 However, these studies were based on surveys and did not provide an exact denominator. A recent single-institution prospective study reported that the incidence of periorbital infection was 0.07% among 4,076 consecutive strabismus operations.3 A few studies have reported a higher incidence of infections after strabismus surgeries in children than in adults.2,4 Our study by contrast found a similar rate of infections in children and adults (children, 0.108%; overall, 0.111%). Endophthalmitis is the most serious complication following strabismus surgery. A few studies have reported the incidence of endophthalmitis following strabismus surgery to be between 1:3,500 and 1:185,000.1,5,6 In a recent study using the Dutch registry of Strabismus Operations, the incidence of postoperative endophthalmitis was reported to be approximately 1 per 11,000 strabismus surgeries.7 However, all of these studies used an approximate number of strabismus surgeries as a denominator. We found an incidence of endophthalmitis of 0.007% (approximately 1 per 13,700) among 151,011 strabismus surgeries in the United States. The median age of these patients was 46.0 years.
Our study has some limitations. First, it was conducted using claims data, which did not include clinical data, such as visual acuity, angle of deviation, amount of surgery, and presence of systemic diseases. Moreover, CPT codes do not allow us to determine which horizontal muscle underwent strabismus surgery. While they are specific for the superior oblique muscle, they are not specific for other vertical muscles. Second, miscoding may have occurred when the provider submitted an incorrect diagnosis or procedure code. Third, we could not investigate patient data outside the enrollment period. Hence it is possible that the first strabismus surgery in the enrollment period might have been a reoperation; to minimize this error, we analyzed whether the strabismus reoperation ICD code (67332) was used for the first strabismus operation during the enrollment period. Fourth, we could not assess risk factors for postoperative endophthalmitis due to the small number of patients who developed endophthalmitis. Future work is needed to determine which factors contribute to the development of endophthalmitis, and to investigate the vulnerability of children versus adults and the role of prior intraocular surgery, as this was not possible within the constraints of the current study.
In conclusion, our study showed that infectious complications after strabismus surgery occurred in approximately one per 900 strabismus surgeries and endophthalmitis in one per 13,700 strabismus surgeries using claims data from a geographically diverse population spanning all 50 states of the US thereby reflecting real-world practice.
Supplementary Material
Financial support:
National Institutes of Health Grants P30 EY026877 and Research to Prevent Blindness Inc. The sponsor or funding organization had no role in the design or conduct of this research. Data for this project were accessed using the Stanford Center for Population Health Sciences Data Core. The PHS Data Core is supported by a National Institutes of Health National Center for Advancing Translational Science Clinical and Translational Science Award (UL1 TR001085) and from internal Stanford funding. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Footnotes
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