This is a single-center, prospective, randomized controlled trial evaluating type A botulinum toxin injection and prism therapy for the treatment of small-angle acute acquired concomitant esotropia.

Specific Aim 1 (Primary): To compare the reduction of deviation angle and improvement of diplopia symptoms between botulinum toxin injection and prism therapy for the treatment of small-angle acute acquired concomitant esotropia.

Specific Aim 2 (Secondary): To compare the improvement of visual functions between botulinum toxin injection and prism therapy for the treatment of small-angle acute acquired concomitant esotropia.

Acute acquired concomitant esotropia (AACE) belongs to the category of concomitant strabismus, which manifests as sudden onset, often accompanied by diplopia, and no change in the strabismus angle of each eye position. In recent years, with the increase in the use of smartphones and other screen devices, the incidence of AACE has been on the rise. Commonly used treatments in clinical practice include surgical treatment, botulinum toxin injection, and prism treatment. Patients with large deviation angel generally require surgical intervention to fundamentally correct their eye position and eliminate diplopia, but surgical treatment requires waiting for six months and can only be performed after the patient's strabismus degree is stable, and there is a risk of intraoperative trauma and secondary surgery. Patients with early and small-angle strabismus often choose prism treatment.

The principle of prism treatment is light refraction. After the light is refracted through the prism, it falls on the fovea of the strabismic eye, eliminating diplopia. In the treatment of AACE, the main target population of prisms is patients with mild strabismus (the strabismus angle is usually less than 25 PD. Wearing prisms can eliminate diplopia and relieve related symptoms, but it does not really correct the patient's strabismus problem.

Botulinum toxin treatment is to inject botulinum toxin type A into the medial rectus muscle to weaken the muscle strength and improve strabismus. Although it has not been widely used in clinical practice, a large number of studies have compared the efficacy of botulinum toxin treatment and surgical treatment. Some studies have found that the efficacy of the two is equivalent, which indicates that botulinum toxin treatment may be a good treatment option for AACE. Botulinum toxin treatment has the advantages of simple operation, low patient cooperation requirements, fast recovery, low trauma, and low treatment cost. It may become a treatment option for patients with small angle AACE. There are also reports that temporary ptosis and overcorrection may occur after botulinum toxin injection. The safety of botulinum toxin injection treatment also needs to be explored. However, existing studies have not fully explored the effectiveness and safety of botulinum toxin in the treatment of small-angle AACE, nor have studies compared the therapeutic effects of prisms and botulinum toxin on small-angle AACE.

In order to better guide clinical practice, we conducted this prospective cohort study to objectively evaluate and compare the therapeutic effects of botulinum toxin and prism treatment on AACE. It is expected that the results of the study will provide more treatment options for AACE patients and provide important guidance for the clinical selection of appropriate methods to treat small-angle AACE.

Inclusion Criteria:

1. acute acquired concomitant esotropia diagnosis (sudden onset of esotropia or diplopia, no significant change in the degree of strabismus in each eye position, and no limitation in eye movement)
2. strabismus angle ≤ 25PD
3. best corrected visual acuity of both eyes ≥ 1.0
4. intracranial disease is excluded by cranial CT or magnetic resonance imaging

Exclusion Criteria:

1. reduction of strabismus angle by more than 10 prism diopters after refractive correction
2. history of other ocular diseases or ocular surgeries
3. presence of organic brain lesions or systemic diseases

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