In this study, 60 patients with AACE received our treatment. The study included significantly more male patients were than female patients (42:18). Excessive near work appeared to be an important risk factor for AACE in patients > 14 years of age; among the population included in our study, the average time devoted to near work was 11.4 ± 2.48 hours per day. This value is similar to those reported previously [2, 4, 5]. Mental stress may also be involved in the occurrence of esotropia. However, for children < 14 years of age, the relationship between near work and AACE was not obvious. This type of AACE is more like late-onset concomitant esotropia in childrenare more likely to have late-onset concomitant esotropia . We also found that convergence force was significantly greater than divergence force in these AACE patients. Sustained near work may enhance the force generated by the medical rectus muscles.
Patients with AACE are willing to choose botulinum toxin injection treatment because of its advantages: simplicity, convenience, minimal trauma, and low cost. In this study, 40 of 60 patients (66.6%) chose botulinum toxin injection treatment, including 31 adults and adolescents with age ≥ 14 years .
Botulinum toxin was first used to treat strabismus in 1979. Currently it have been used to treat various types of strabismus. One of most important indications for botulinum toxin is the treatment of infantile esotropia[1, 2, 9, 11–13]. Of course, it is also used to treat pediatric acute-onset acquired esotropia[1, 2, 9, 12]. For example, Wan et al.compared the effects of botulinum toxin injection vs. surgery in children with AACE. There were 16 patients in the botulinum toxin group and 33 patients in the surgery group. The results showed no significant difference in the success rate between groups at 6 months (81% vs. 61%, P = 0.20) or at 18 months (67% vs. 58%, P = 0.74). The median angle of deviation and median stereoacuity were similar between groups at 6 and 18 months.
Generally speaking, the younger a patient, and the smaller the angle of strabismus, the better the treatment effect.[11, 12, 16, 17, 19] The effects of botulinum toxin in infants and children with squint are quite good, but the effects of botulinum toxin when used to treat constant squint in adults are uncertain. Recently, we found some authors reported the use of botulinum toxin to treat adult AACE [1, 2]. Wang described 6 AACE patients, aged 3–34 years, who were treated with botulinum toxin. The study included 3 patients aged > 14 years. The overall success rate in the study was 83.3 (5/6). In another recent study of 13 patients with AACE (age 3–24 years, average age 12.61 ± 6.74 years)in the botulinum toxin injection group ,also included adult patients. Although the authors do not clearly indicate those adult patients treatment results, we speculate that botulinum toxin was effective for them. So far, we have not found a study focused on botulinum toxin in the treatment of adult AACE.
In our study, 40 patients with AACE chose botulinum toxin injection therapy, including 31 patients > 14 years of age. After three doses of treatment, only 2 adult patients did not meet the criteria for cure. The treatment success rate reached 95%. Certainly, the treatment effect was not as great as observed in patients younger than 14 years of age. In the adult group, the residual angle of deviation after treatment was higher than in the pediatric group; 18 cases (58.0%) had esophoria after treatment, and 9 patients (29.0%) relapsed after 6 months of treatment. In the pediatric group, all 9 patients reached orthotropia after two dose of botulinum toxin injection, and no patients had relapse.The final treatment success rate was significantly different between the two groups( 64.5% vs 100%) .We speculate that, with an extended follow-up period, the chance of recurrence in the adult group may continue to increase. We believe that relapse in these patients is related to residual implicit deviation on the one hand, and continued excessive use of mobile phones on the other.
In general, the efficacy of botulinum toxin in the adult group was satisfactory. In addition to the mechanism of action of botulinum toxin that have reported by other studies[21–23], we speculate that it is also related to the characteristics of AACE. First, most adult patients with AACE had a relatively small esotropia angle. Second, the time elapsed since symptom onset was brief. AACE is an acute strabismus. The time from onset to treatment is generally within 2 years, usually about a few months. Therefore, after treatment, the extraocular muscles have a greater chance of remodeling and recovery. Other types of adult strabismus often start in childhood. Third, these patients have the potential for stereopsis. After treatment, stereopsis is re-established and plays a role in controlling eye position, so that the treatment effect can be sustained. In this study, all cured patients had relatively normal stereopsis after treatment, as determined by synoptophore or random-dot stereopsis pictures.
Only 20 patients in this study chose extraocular muscle surgery. Those patients had relatively large angles of esotropia (mean 44.0 ± 11.4 PD at distance and 39.6 ± 11.0 PD at near).
In the early years of AACE surgery, the undercorrection rate was very high, reaching 75%. Many of these patients required additional strabismus surgery. The reasons may be related to the prism-eating phenomenon caused by mechanisms that compensate for the deviation. Application of the prism adaptation test (PAT) significantly improved the success rate of surgery in AACE patients[6–8] However, the PAT itself requires a long time, especially for patients with high strabismus angles. It is difficult for these patients to wear prisms for several days. Some authors, including us, prefer to reduce the incidence of undercorrection and avoid the time and expense associated with PAT by increasing the amount of the correction during surgery[2, 3, 10] We increased the amount of surgery by 1–2 mm beyond what is typical for esotropia surgery.The results showed that the treatment effect was similar to that achieved with botulinum toxin injection. Three of the 20 patients (15%) underwent suture adjustment due to the undercorrection of esotropia, and 4 patients(20%) relapsed after half a year. Only 13 patients (65%) had satisfactory results after one operation. Therefore, it is still a challenge for strabismus correction doctors to determine the target surgical volume more conveniently and accurately for AACE patients.
In this study, 7 patients (17.5%) in the botulinum toxin injection group experienced monocular ptosis of the upper eyelid about one week after injection, and all recovered spontaneously within 1–3 months. No other obvious complications occurred. Therefore, surgery as well as botulinum toxin injection are safe for AACE patients.
During the same period, 16 patients who did not choose surgery or botulinum toxin treatment were followed through in-person visits to the hospital or via telephone. None of the symptoms of these patients improved. A study has reported that the esotropia of some patients may be improved or even resolved by reducing the time spent using mobile phones. This phenomenon did not appear in our patients. One of the important reasons may be that people are becoming more and more reliant on electronic products, especially smartphones, and it is difficult to effectively reduce the time spent on near-work.
This study has some limitations. First of all, for ethical reasons, we did not randomly group patients, resulting in a relatively small number of surgical patients. There was a significant difference in the angle of deviation between groups before treatment, which made the comparison of treatment effect between groups difficult. In addition, the follow-up period was not sufficiently long, and the long-term stability of these treatment effects needs further observation.