Introduction

Infantile esotropia is defined as an inward ocular misalignment that develops before 6 months of age;¹ however, its pathogenesis remains unknown. The existing theory suggests that mutations or disturbances extending subcortical neuroplasticity beyond the neonatal period contribute to inward eye deviation.² Globally, the incidence of infantile esotropia ranges from 0.1% to 1%.³

Treatment options for ocular misalignment in infantile esotropia include nonsurgical and surgical approaches. Nonsurgical treatment, such as Botox injections, has shown promising results either alone or as an adjunct to surgery.⁴ However, surgery remains the preferred treatment for cases of persistent infantile esotropia. Previous studies advocate for early surgical intervention, ideally before 2 years old, to maximize the chance of regaining binocularity, which ranges from 13.5% to 36.4%.^5,6 and diminishes over time. Surgery aims to achieve an orthotropic or at least a monofixation range.⁷ Depending on the specific case, surgical techniques may involve a pure horizontal muscle surgery or a combination of horizontal and oblique muscle surgeries.

Globally, the success rates of surgical outcomes for infantile esotropia vary widely, ranging from 23%–94.11%,^7–19 due to differences in participant characteristics and the success criteria used. Among two-muscle surgeries, bilateral medial rectus recession is the most common procedure, with success rates of 56.45%–80.70%.^7,9,10,15 The unilateral recession-resection technique is also effective, with success rates of 30.97%–78.9%.^7,9,16 Additionally, studies involving Asian populations report success rates of 52%–90.27%.^7–9,11,12 However, the association between the type of strabismus surgery (ie, symmetrical or asymmetrical) and successful outcomes remains controversial. The literature lacks consistency in successful outcomes regarding the types of surgical procedures. Moreover, there is a lack of data on success rates within the Thai population, and the prognostic factors influencing surgical outcomes in infantile esotropia remain unknown.

Our study aims to report the success rate of surgery in infantile esotropia in a tertiary hospital setting in Thailand, as well as to factors associated with its success.

Materials and Methods

This is a retrospective cohort study, which collected from electronic data from the outpatient and inpatient clinics of Phramongkutklao Hospital from January 1, 2013 to June 30, 2023.

Participants

The study included patients with infantile esotropia who regularly followed-up for at least 3 months. The ICD10 code “H500, comitant esotropia” and ICD9 code “15.1–15.9” were used to search for the population of patients with esotropia. Participants with other causes of esotropia, incomplete data, incomplete follow-up, previous surgeries, coincidental intracranial abnormalities, and ocular diseases were also excluded from our study. The flowchart of participant recruitment is shown in Figure 1.

Figure 1 Flowchart of participant recruitment.

Disease Definition

Infantile esotropia is defined as an inward eye deviation before 6 months of age. Additionally, signs of disruption of binocular vision, including dissociated vertical deviation, latent nystagmus, or asymmetrical smooth pursuit, might be associated features.

Surgical Intervention

Three surgical techniques were employed in this study: unilateral medial rectus recession, unilateral medial rectus muscle recession combined with lateral rectus muscle resection, and bilateral medial rectus recession. The surgical dosages were determined using the Marshall Parks table as a reference. Surgical success was defined as having a postoperative angle of less than 10 prism diopters (PD) using the alternate cover test technique.

Data

General demographic data, preoperative evaluation, surgical techniques, and postoperative outcomes were collected. Visual acuity was measured with a LogMar value. Refraction was measured by subjective refraction from one optometrist. Spectacles were prescribed for best-corrected visual acuity.

Statistical Analysis

Descriptive statistics were used to obtain the basic data of the sample group from the general data. Group data regarding the amount and percentage of quantitative data were also analyzed. The Shapiro–Wilk test was used to assess data normality. If the data significantly deviated from normality, nonparametric tests were used for analysis. For normally distributed data, the mean and standard deviation were measured. For non-normally distributed data, the average value was summed with the median. Numbers and percentages represent clustered data. The Mann–Whitney U-test was employed to compare differences between groups for continuous variables with non-normal distributions. Fisher’s exact test was applied to assess associations for categorical variables, particularly with small sample sizes. These tests were chosen for their suitability in analyzing non-normal data and ensuring reliable group comparisons.

Logistic regression was used to evaluate associated independent risk factors for successful surgery. Visual acuity was categorized as either good or poor vision (LogMar < 0.4 and ≥ 0.4, respectively). The preoperative strabismus angle was classified as either small or large (<50 and >50 PD, respectively). The types of surgery were classified into three groups: recession-resection, bilateral recession, and other procedures. Logistic regression was used to adjust for the number of surgical muscles, surgical technique, age, visual acuity, refraction, preoperative angle, and mean onset duration. Statistical significance was set at p <0.05, and Stata 14 (StataCorp LLC, the USA) was utilized for analysis.

Ethics Approval

The study was approved by the Institutional Review Board of the Royal Thai Army Medical Department (approval number S077h/66_Exp). Due to its retrospective nature, the need for informed consent was waived by the Royal Thai Army Medical Department. This study was conducted in accordance with the principles of the Declaration of Helsinki.

Results

The demographic data is shown in Table 1. The study included a total of 77 participants with infantile esotropia who underwent surgical correction at our tertiary hospital between 2013 and 2023. The mean age at the time of surgery was 9.54 ± 10.87 years. The mean follow-up time was 6.8 ± 0.42 months. The mean visual acuity was 0.41 ± 0.48 logMar. The mean refraction was −1.04 ± 4.16 diopters. The mean onset duration of esotropia detection was 9.34 ± 10.9 years. Stereopsis records were available for 30 participants, in which 16 exhibited measurable stereopsis. The mean preoperative stereopsis for these 16 cases was 1406.25 ± 590.25 arcseconds.

Table 1 Mann–Whitney U and Fisher’s Exact Tests for Preoperative Demographic Characteristics

Bilateral medial rectus recession was the most common surgical technique in our data set, at 66.2% (51/77). In comparison, unilateral recession and resection comprised 18.2% (14/77) of cases, while unilateral muscle surgery accounted for 15.6% (12/77). Recession-resection procedures yielded excellent results in all cases (14/14), while 62.7% (32/51) and 75% (9/12) of bilateral medial rectus recession and unilateral muscle surgeries, respectively, were considered successful.

Table 2 shows the postoperative data. Postoperative alignment success was achieved in 71.4% of patients at the final follow-up. The mean preoperative deviation was 49.52 ± 14.9 PD, and this improved to 5 ± 7.07 PD postoperatively. The mean postoperative stereopsis was 1296.87 ± 426.64 arcseconds at 6 months. No complications were reported in our study population. The reoperation rate was 15.6% (12/77) of patients, primarily due to residual esotropia.

Table 2 Mann–Whitney U and Fisher’s Exact Tests for Postoperative Demographic Characteristics

Table 3 presents the logistic regression analysis for successful surgical outcomes. Having a smaller preoperative deviation of <50 PD was significantly associated with successful outcomes, with an adjusted odds ratio of 7.13 (95% CI, 2.04–24.86; p < 0.05).

Table 3 Logistic Regression of Success in Infantile Esotropia Surgery

The reoperation rate in our study was 15.6% (12/77), mainly due to residual strabismus. All these cases underwent bilateral medial rectus recession.

Discussion

The success rate of surgery in our cohort was 71.4%, which is in line with previous reports.^7–14 The results of our study indicate favorable alignment outcomes for surgical intervention for infantile esotropia, particularly when performed under specific conditions. Notably, having an initial ocular deviation angle of <50 PD was identified as a prognostic factor associated with successful surgical outcomes, and this is consistent with previous literature.²⁰ This association can be attributed to the relative ease of surgically correcting smaller deviations, resulting in a more precise postoperative alignment. Trigler et al²¹ demonstrated that patients with esotropia with smaller deviation angles had better alignment outcomes and required fewer reoperations. Having smaller deviations may also indicate less severe underlying ocular motility issues, making surgical correction more straightforward and effective. Our data also suggests that two-muscle surgeries may be inadequate for larger angles, which need three or more muscle surgeries. This finding parallels results in populations with exotropia, wherein smaller preoperative strabismus angles were similarly associated with better outcomes.^22–25

The type of surgical procedure did not yield an odds ratio value in the logistic regression analysis because all cases in the recession-resection group were successful, and thus there was no data for the nonsuccess group. Nonetheless, our data suggests that recession-resection surgery produced more favorable outcomes versus other procedures in our cohort, indicating it may be particularly effective for infantile esotropia. However, our findings differ from those reported by Kim et al⁹ and Singh et al,⁷ who found higher long-term success and lower reoperation rates with bilateral recession compared to the recession-resection technique. The differences in outcomes between bilateral medial rectus recession and unilateral recess-resect surgeries highlight their distinct approaches and impact on postoperative success. Bilateral medial rectus recession, which involves equally weakening both medial rectus muscles, is often preferred for its balanced approach, because it typically leads to more stable long-term ocular alignment and lower reoperation rates. Conversely, unilateral recess-resect, which includes recessing the medial rectus and resecting the lateral rectus of the same eye, offers a more targeted correction for severe misalignments, but it is associated with more variable long-term outcomes and a higher chance of reoperations. Previous evidence revealed comparable outcomes between the two operations,^15,26 whereas other studies showed better outcomes and a lower reoperation rate in bilateral recession versus the recess-resect procedure.^7,9,27 While these are general trends, our study found all cases of recess-resect to be successful, suggesting that it can yield promising results in certain situations. These findings emphasize the need for further prospective, multicenter studies to comprehensively compare these surgical techniques and refine treatment protocols based on individual patient characteristics.

Beyond achieving ocular alignment, this study demonstrated improved binocular vision 6 months postoperatively. This enhancement in stereopsis aligns with previous research reporting improvements of 5%–30%.^10,12,14,15 Recent evidence suggests that earlier surgical intervention leads to greater binocular gains compared with later surgery.^7,11 Although this study did not show a significant impact of early surgery on binocular function, the findings support surgery even after a late diagnosis, as it might still promote binocular function. However, owing to the limited stereopsis data, this factor could not be included in the logistic regression analysis of successful surgical outcomes.

The old age of participants in this study reflects the tendency for delayed surgery in infantile esotropia cases within the setting. Although this study showed improved stereopsis postsurgery in the successful and unsuccessful groups, the difference was not statistically significant when comparing preoperative and postoperative measures. This limitation might be attributed to the referral system and shortage of healthcare providers, which delay timely intervention. These findings highlight the need for health policies that promote earlier detection and surgical intervention, as delayed surgery is associated with poorer motor and sensory outcomes compared with early intervention.^7,11,18

The findings underscore the high success rate of surgical intervention in achieving successful motor outcomes for infantile esotropia. Identifying smaller deviation angles as prognostic factors should guide clinicians in their decision-making process, allowing them to inform patients most likely to benefit from long-term ocular alignment surgery. Additionally, surgery in infantile esotropia improves stereopsis, even when performed later. The strengths of this study include a large patient population, identification of key prognostic factors for successful outcomes, comprehensive data collection, and the expertise of an experienced surgical team. These factors enhance the reliability of our findings, which provide valuable clinical insights for managing infantile esotropia.

Despite the aforementioned strengths, the study’s retrospective design and single-center setting limit the generalizability of the findings. Additionally, the variability in follow-up duration may have impacted the consistency of long-term outcome assessments. Future research should involve prospective, multicenter studies with standardized follow-up protocols to validate these findings and assess the long-term outcomes of surgical correction for infantile esotropia. Additionally, investigating the impact of different surgical techniques, timing, and genetic and environmental factors can help refine treatment strategies and improve patient-specific outcomes.

Conclusion

The cohort demonstrated a 71.4% success rate of surgery for infantile esotropia, and having a smaller preoperative angle (<50 PD) was significantly associated with better outcomes. Identifying prognostic factors can aid in patient selection, care, and prognostic advice. Further studies are required to support their association, as well as analyze additional prognostic factors that can influence the success of surgery.