Botulinum toxin not as effective as extraocular muscle surgery in Acute Acquired Comitant Esotropia
Esotropia is a common type of strabismus that mostly occurs after infancy or during childhood, but it could appear in adults or even the elderly. Acute acquired comitant esotropia (AACE) is a subtype of esotropia defined by acute onset, the same deviation angle in all directions of gaze, and normal ocular motility. AACE can have various causes such as visual deprivation, refractive error, neurological abnormality, and excessive near work. The incidence of AACE appears to have risen in recent years, which may be attributable to increased computer and smartphone use. Moreover, the COVID-19 pandemic has led to more people working and studying online, which may aggravate the condition.
AACE may reduce the quality of life, causing diplopia, impaired stereopsis, and/or cosmetic, social, and amblyopic problems, the latter of which may lead to poor vision and blindness in children. Currently, choices for treatment include horizontal rectus muscle surgery and botulinum toxin injection. Due to the increasing number of AACE patients and insufficient hospital resources, the waiting list for surgery can be extremely long. In such cases, botulinum toxin may be employed as an alternative treatment. However, its rate of success remains unclear, as does the duration of its effect.
The aim of this study by Suwannaraj et al was to compare the success rate of strabismus surgery with that of botulinum toxin injection and compare the results in different magnitude of deviation angle in a larger series of AACE patients.
This is a retrospective cohort study in which authors treated 34 patients of AACE with botulinum toxin compared with 80 patients who had been treated with surgery. The data included angle of deviation in prism diopter (PD) at baseline and one, three, and six months after treatment. The main outcome was the success rate in each treatment group.
In the surgery group, mean esodeviation angles at baseline and one, three, and six months after treatment were 50.8 ± 18.3 PD, 4.9 ± 8.3 PD, 4.6 ± 9.5 PD, and 5.5 ± 10.3 PD, whereas those in the botulinum toxin group were 51.2 ± 14.3 PD, 13.9 ± 17.4 PD, 22.0 ± 19.3, and 31.3 ± 23.8 PD, respectively. There was a statistically significant difference in the deviation angles between the two groups (p < 0.001). The success rate in the surgery group at one, three, and six months was 81%, 84%, and 79%, whereas that in the botulinum toxin group was 50%, 27%, and 27%.
Currently, there are various choices for AACE treatment, two of which are conventional horizontal rectus muscle surgery and botulinum toxin injection. The principle of both treatments is to weakening the medial rectus muscle. Common choices of surgery can be either recession of the medial rectus and resection of the lateral rectus muscle in the deviating eye or medial rectus recession in both eyes. Botulinum toxin treatment, in the same manner, can be either injection at medial rectus in deviating eye or medial rectus muscles in both eyes. In this study, patients with AACE received either botulinum toxin injection or horizontal rectus muscle surgery. Generally, the younger the patient and the smaller the preoperative angle of deviation, the better the treatment effect. However, in our study, age at treatment and preoperative angle of deviation did not differ significantly between the two groups. Our study demonstrated that the horizontal rectus muscle surgery was more effective than botulinum toxin injection in the treatment of AACE in all subgroups and all time periods (one, three, and six months after treatment). The success rate in the surgery group reached 81.3% at one month after surgery and then declined slightly to 78.8% at six months. However, in the botulinum toxin group, it was only 50% at one month after injection and declined to just 26.5% at six months. The success rate of surgery was also higher in both preoperative deviation angle subgroups.
Botulinum toxin injection was not as effective as conventional surgery in AACE patients, and its effects were temporary. However, it had some therapeutic effect, and the procedure is simple, rapid in action, and has no serious side effects. This may be considered as a chance for patients not preferring surgery.
Source: Suwannaraj et al; Clinical Ophthalmology 2023:17
https://doi.org/10.2147/OPTH.S401019
