Surgical outcomes of unilateral medial rectus recession for partially accommodative esotropia
Partially accommodative esotropia (PAET) is composed of accommodative and non-accommodative components. After full hyperopic correction, various options such as occlusion, prismatic correction, botulinum toxin injection, and surgical intervention have been attempted to treat the residual esotropia – . Residual esotropia of ≥ 10–15 prism diopters (PD) with poor binocularity is generally managed surgically , , , however, long-term surgical results are disappointing because PAET develops at a relatively early age of 2–3 years , with immature stereopsis, resulting in a high rate of under-correction , , , postsurgical drift, or decompensation occurring during long-term follow-up, together with the change in hyperopic refractive errors as the patients grow . Therefore, various approaches have been made to achieve successful surgical outcomes. In the preoperative stage, a prism adaptation test is suggested to determine the optimal surgical target angle , . Regarding surgical techniques, comparing the results of single and multiple muscle surgery , the efficacy of concurrent botulinum toxin injection during surgery and that of faden operation or augmented surgery , , has also been demonstrated in previous studies. The optimal management of small to moderate angle PAET is not well understood. Early surgery may be beneficial in those with a suboptimal fusional response with prism glasses – . In our previous report of PAET patients showing successful motor fusion with prism glasses, only 7.3% of patients were successfully weaned off prism glasses and at the same time gained good motor fusion. The rest may need surgery to remove the prisms . Therefore, it is necessary to investigate the course and outcomes of surgery in PAET. To the best of our knowledge, the long-term surgical outcomes of unilateral medial rectus (UMR) recession for small to moderate angle PAET have not been reported. Determining whether fusion can be obtained or wearing of prism glasses can be weaned off with only one muscle surgery in patients with small to moderate angle PAET is meaningful. Herein, in this study, we aimed to evaluate the effectiveness of UMR recession in patients with PAET with a residual esotropia of less than 25 PD after full hypermetropic correction.   Twenty-eight patients fulfilled the inclusion criteria (Table ). The mean age at which esotropia was first observed by their parents was 3.2 ± 1.8 years (range, 0.3–7.0 years), and the age at surgery was 7.3 ± 2.0 years (range, 2.5–10.0 years). The mean surgical dose of UMR recession was 5.6 ± 0.7 mm (range, 4.0–7.0 mm) for correcting esotropia of 15.5 ± 3.7 PD (range, 10–25 PD) at distance fixation. Clinical manifestations were compared preoperatively and at the last follow-up examination (Table ). BCVA was significantly improved from 0.13 to 0.06 LogMAR in both eyes ( P = 0.006 in the right eye, P = 0.008 in the left eye). Refractive errors significantly decreased from + 2.91 ± 1.92 D to + 1.09 ± 2.69 D ( P < 0.001). Stereoacuity was not significantly different before and after surgery ( P = 0.508 in the W4D test, P = 0.626 in the Randot test). Changes in the angle of esodeviation after surgery are demonstrated in Fig. . The mean preoperative angle of esodeviation, 15.5 ± 3.7 PD at distance fixation, was significantly decreased to 7.3 ± 8.8 PD at 1 month postoperatively ( P < 0.001). During follow-up, the angle of esodeviation was 7.7 ± 9.9 PD at 6 months, 7.3 ± 11.9 PD at 1 year, and 6.2 ± 13.8 PD at the last follow-up visit. No significant difference in the angle of deviation at distance was observed at any time point ( P = 0.787 by repeated measures ANOVA). The rate of postoperative change in esotropia was 0.1 ± 1.3 PD/month from 1 month to 6 months postoperatively. Subsequently, esodeviation decreased at an average rate of 0.1 ± 1.2 PD/month from 6 months to 1 year postoperatively, and 0.0 ± 0.2 PD/month from 1 year postoperatively to the last visit. The rate of postoperative change in the angle of deviation was not significantly different in each period ( P = 0.703 and P = 0.903, respectively). No significant difference in the angle of deviation at near fixation was observed at each postoperative time point ( P = 0.834 by repeated measures ANOVA). Successful surgical outcome was defined as phoria of ≤ 5 PD based on the final distance alignment. Success rates were 39.2% at 1 month, 32.1% at 6 months, and 39.3% at 1 year postoperatively. At the last follow-up, 15 patients (53.6%) had surgical success, and 13 patients (46.4%) had failure; 3 (10.7%) had consecutive exotropia of > 5 PD, and 10 (35.7%) had residual esotropia of > 5 PD. Comparison of the characteristics of surgical success and failure groups are listed in Table . The mean age at surgery was 8.3 ± 1.4 years in the success group, which was older than 6.3 ± 2.1 years in the failure group ( P = 0.005). The interval between the age of onset and time of surgery was longer in the success group than in the failure group ( P = 0.002). The duration of prismatic correction before surgery was significantly longer in the success group than in the failure group ( P = 0.034). The amount of UMR recession was significantly larger in the success group with 6.0 ± 0.4 mm than that in the failure group with 5.2 ± 0.6 mm ( P < 0.001). Further, no significant differences were observed between the two groups.   For the surgical management of esotropia, deciding whether to perform unilateral or bilateral MR recession varies depending on the amount of deviation, type of esotropia, and the surgeon’s preference , , . Because of the merit of less operating time, less potential complications and preventing overcorrection, there have been many reports describing the success of UMR recession in patients with esotropia. Procianoy and Justo mentioned that esotropia of 15–35 PD were treated with 6–8 mm UMR recession and achieved 96% of surgical success without overcorrection. Stack et al. have reported that a 6 mm UMR recession resulted in 13.2 PD total change in deviation, and one muscle surgery was adequate for esotropia < 25 PD. Grin and Nelson have also reported that a UMR recession of 6–6.5 mm is a safe method for treating moderate-angle esotropia of 30–35 PD, with a success rate of 80%. However, direct application of these positive outcomes of UMR recession to PAET should be considered carefully because the main cause of surgical failure of PAET is undercorrection or postoperative drift to esodeviation , , . It is clear that multiple muscle surgeries are performed for the treatment of large-angle of PAET . However, determining the number of surgical muscles required for the treatment of small- to moderate-angle PAET remains a concern. Therefore, we aimed to investigate the efficacy of UMR recession for treating PAET ≤ 25 PD and achieving complete weaning of prism glasses. As a result, the success rate was 53.6% at 4.4 ± 3.1 years postoperatively. The surgical success rate of UMR recession in various types of esotropia, resulting in a favorable deviation of ≤ 10–12 PD, ranges from 80 to 100%. 15, , , The success rate of our study is lower than that which may be attributed to the relatively long postoperative follow-up period of 4.4 years and a strict success criteria within 5 PD of phoria. Furthermore, the success rate was only 10% among the 10 patients who underwent UMR recession of ≤ 5 mm in our study. The mean surgical amount of these 10 patients was 4.9 ± 0.3 mm (range, 4–5 mm). This indicates that a sufficient amount of recession of more than 5 mm is required to manage PAET effectively. In our study, three patients were overcorrected with consecutive exotropia of > 5 PD, who had undergone 4.5–5 mm recession for treating 14–19 PD of esotropia. In all of these patients, immediate overcorrection of more than 10 PD was found at 1 month after operation, and at the last follow-up examination, their exodeviation were 8 PD, 10 PD, and 28 PD at distance fixation, respectively. No specific risk factor for overcorrection was identified, such as surgical age at surgery, angle of preoperative deviation, period of wearing prism glasses, degree of stereoacuity, presence of amblyopia, history of preterm birth, and degree of hyperopia, probably due to the small number of patients. In previous reports regarding surgical overcorrection of esotropia, a history of cerebral palsy and preterm birth were mentioned as risk factors of surgical overcorrection , . In spite of the reduced amount of MR recession, esotropia with cerebral palsy resulted in a greater surgical response, and the significantly higher incidence of late overcorrection than patients without cerebral palsy . In addition, the surgical dose-response was significantly greater in preterm patients than in full-term patients with infantile esotropia . Common mechanisms mentioned in these studies include abnormal cortical reflexes in patients with neurological deficits, defective substrate of binocularity and muscle tone abnormality. However, authors could not find risk factor corresponding to hypothesis of previous research because there are only three patients with overcorrection in our study and none of them had any neurological deficits, or developmental delays. Future studies with a large number of enrolled patients will be meaningful. Many studies have demonstrated that stereopsis improves after strabismus surgery for PAET , . Kim and Cho have reported that patients with partial stereopsis increased from 20 to 78% after surgery, and the prognosis for stereopsis of PAET was favorable, which is different from congenital esotropia that causes consistent low stereopsis throughout one’s life. Kurup et al . also demonstrated favorable postoperative sensory outcomes of 100 arcsec. Unlike previous studies , , good fusional response in W4D test and degree of stereopsis in the Randot test were not significantly changed after surgery in our study. Moreover, no significant differences in binocularity or stereopsis were observed between the success and failure groups. Regarding this result, the authors believe that the binocularity and stereopsis of enrolled patients were already preserved through wearing of prism glasses preoperatively. We have previously reported the efficacy of prismatic correction in PAET , . In that study, 30.6% in PAET with ≤ 20 PD achieved binocular fusion and stable alignment of ≤ 10 PD after 3 years of prism-wear. In the present study, 23 patients (82.1%) were treated with preoperative prismatic correction for improving binocularity, and the mean period of prism glasses wearing was 27.7 ± 29.0 months. Hence, 64.3% of the patients in this study demonstrated good fusional responses with the W4D test preoperatively, and this value was higher than that in previous studies of 14.3–35% , . This study also evaluated clinical factors affecting surgical outcome. As a result, older age at surgery, longer time to wear prism glasses before surgery, and receiving a sufficient amount of surgical correction may improve the rate or surgical success. The duration of wearing prism glasses before surgery was significantly longer in the success group than that in the failure group. Although the patients in this study could not obtain stable ocular alignment of < 10 PD even with prismatic correction and eventually required surgery , it can be seen that sufficient prismatic correction before surgery may contribute to improve surgical outcomes. In addition, the longer period of wearing prism glasses in the success group compared to the failure group may be one of the reasons why the age at surgery is older in these patients. In previous studies regarding factors affecting surgical outcomes in PAET, deteriorated refractive esotropia, severe anisometropia, increasing hyperopia with age were mentioned as risk factors of poor surgical outcome . However, in this study, there were no significant differences in the degree of stereopsis and hyperopia between the success and failure groups. Kurup et al . mentioned that preoperative refractive error did not play a significant role in surgical outcomes, which is comparable to our results. The mean preoperative refractive errors of +3.1 ± 1.7 D in the success group was not statistically significant different from ± 2.7 ± 2.2 D in the failure group. This indicates that the degree of hyperopia did not play a role in surgical outcomes, which is similar to those of previous studies , , demonstrating that preoperative refractive errors were not different among the favorable, under-corrected, and over-corrected groups. The limitations of this study include its retrospective nature and small sample size of 28 patients. However, although our study was conducted with a small number of patients, the result of this study is valuable in that no previous studies that included a long-term observation of one muscle surgery in PAET. Additionally, as a second limitation, patients with amblyopia were enrolled. Amblyopia was treated with glasses and occlusion therapy as much as possible; however, amblyopia persisted despite sufficient treatment in three patients (10.7%). Further evaluations with more patients and strict exclusion criteria would be meaningful. Furthermore, direct comparison of our study to those of previous studies regarding the surgical outcome of UMR recession were not possible as the surgical dose and indications of PAET varied depending on the surgeons’ experience, preference and patients’ characteristics. In conclusion, successful results of UMR recession were obtained in 53.6% of patients with PAET of 25 PD or less. Considering that the period of wearing prism glasses was longer in the success group, sufficient preoperative prismatic correction for maintaining binocularity can positively influence surgical success. Furthermore, because the amount of hyperopia does not affect the surgical result, modifying the amount of recession according to hyperopia may not be necessary, and full surgical correction based on the maximum non-accommodative component of the deviation may improve surgical success. Finally, sufficient amount of UMR recession of more than 5 mm is required to manage PAET effectively.   This retrospective study was conducted after approval of the Seoul National University Bundang Hospital Institutional Review Board (no. B-2004-607-102), and all procedures adhered to the tenets of the Declaration of Helsinki. Informed consent was obtained verbally from all participants, with their guardians and residents as witnesses.   Medical records of children aged 10 years or younger with PAET who had residual esotropia of ≤ 25 PD at distance measurement after full hypermetropic correction and underwent UMR recession surgery between August 2009 and February 2021 were reviewed. Among them, we included patients who were followed up for at least 1 year postoperatively. The exclusion criteria were as follows: neurological deficits, developmental delays, ocular diseases such as optic nerve and retinal disorders, or a previous history of ocular surgery; with a vertical deviation in the primary position, an A or V pattern, or paralytic or restrictive esotropia.   All patients underwent a complete ophthalmologic examination, including a visual acuity test and cycloplegic refraction with cyclopentolate hydrochloride 1%. Patients underwent full hyperopic correction determined by cycloplegic refraction at the first visit, and prism glasses were prescribed for prismatic correction of residual esotropia at the second visit. Clinical factors, including sex, age at onset, age at surgery, best-corrected visual acuity (BCVA), changes in spherical equivalents (SE) refractive errors, amount of deviation, degree of stereopsis, and the presence of amblyopia were analyzed. Deviations were measured using the alternate prism cover test or the Krimsky method, depending on the patient’s age and cooperation, with fixation at 6 m and 1/3 m on accommodative targets in the fully corrected states of their hyperopia. Measurements of ocular deviation were performed by one examiner (J-M.H.). Amblyopia was defined as a BCVA of < 20/30 in one eye or an interocular difference in visual acuity of ≥ two lines. Mild to moderate amblyopia was defined as a two to five-line decrease in acuity than that in opposite eye. A decrease of ≥ six lines was considered severe amblyopia . Amblyopia was treated with glasses and occlusion therapy during follow-up. Stereoacuity was measured using the Randot stereoacuity test (Stereo Optical Co. Inc., Chicago, IL, USA), and binocular fusion was determined using the Worth 4-dot (W4D) test preoperatively and postoperatively. In the W4D test, only a fusional response of four lights visible was considered normal. Surgery was performed when orthotropia or esophoria < 10 PD was not maintained with prism glasses, or if the patients and/or parents wanted to wean off prism glasses. The target angle was based on the distance deviation measured using the prism and alternate cover tests. All patients were treated with UMR recession of 4 to 7 mm. The amount of UMR recession in this study referred to previous studies , , . 10–20 PD esotropia were treated with 4–6 mm recession, and 20–25 PD were treated with 5–7 mm recession. The surgical amount was adjusted by 0.5 to 1 mm augmentation according to intraoperative forced duction test results of the MR. To prevent overcorrection, in patients with mild hyperopia under + 2.50 diopters (D) of the spherical equivalents or a history of prematurity, the surgical amount was reduced compared to that in other patients with the same angle of esodeviation. Each surgery was performed under general anesthesia by a single surgeon (J-M.H.). The eye for which UMR recession was performed was determined by considering the presence of a dominant fixating eye and the degree of medial rectus muscle tightness through a forced duction test during surgery. Conjunctival incision was made at the superonasal quadrant of the eyeball. Tenon’s capsule was dissected and the MR muscle was isolated using the muscle hook. The muscle was detached from the insertion sited and MR recession was done. Detached muscles were sutured to the sclera and securely anchored to the insertion site of sclera using 6 − 0 vicryl sutures. Conjunctival incision repair with 8 − 0 vicryl was done.   A successful outcome was defined as a phoria of ≤ 5 PD at distance measurement. Surgical success rates were investigated at 1 month, 6 months, 1 year postoperatively, and at the last follow-up examination. Furthermore, based on the angle of deviation at the last follow-up, clinical factors in the success and failure groups were compared to identify the factors affecting surgical success. Statistical analyses Statistical analysis were performed using the SPSS version 22.0 software (IBM Corporation, Armonk, NY, USA). The preoperative and postoperative angles of esodeviation, BCVA, refractive errors, and stereopsis were compared using the paired t-test and McNemar’s test. Using one way repeated measures ANOVA, changes in esodeviation were analyzed at each postoperative time point. Comparisons of clinical factors, such as age at surgery, duration of prismatic correction, refractive errors, and degree of stereopsis, between the success and failure groups were evaluated using the independent t-test and Chi-square test. Statistical significance was set at P < 0.05. For the convenience of statistical analysis, the angles of esotropia and exotropia are expressed as positive and negative values, respectively.   Statistical analysis were performed using the SPSS version 22.0 software (IBM Corporation, Armonk, NY, USA). The preoperative and postoperative angles of esodeviation, BCVA, refractive errors, and stereopsis were compared using the paired t-test and McNemar’s test. Using one way repeated measures ANOVA, changes in esodeviation were analyzed at each postoperative time point. Comparisons of clinical factors, such as age at surgery, duration of prismatic correction, refractive errors, and degree of stereopsis, between the success and failure groups were evaluated using the independent t-test and Chi-square test. Statistical significance was set at P < 0.05. For the convenience of statistical analysis, the angles of esotropia and exotropia are expressed as positive and negative values, respectively.   