2.1

Excessive near work

Excessive near-work activities, including studying and using electronic devices, especially the overuse of electronic devices at night, increase the risk of AACE. In addition, excessive near work can induce convergence spasm, accommodative spasm and anomalies in the sensory and motor fusion, further promoting the occurrence of AACE. Young adults use electronic devices for longer periods compared to other age groups, explaining the higher proportion of young adults diagnosed with AACE in recent years.

2.2

Abnormal fusional vergence

The occurrence of the Swan type is attributed to the disruption of fusion functions. Researchers previously demonstrated that none of the AACE cases they studied fit into traditional classifications, indicating that these cases could be caused by a decreased compensatory capacity for latent esodeviation due to reduced fusion amplitude.

2.3

Abnormal convergence and accommodation

A research based on 22 patients revealed that the patients had a higher ratio of accommodation-convergence to accommodation and accommodative insufficiency than healthy subjects. The findings showed that patients required more convergence effort when viewing nearby objects due to accommodative insufficiency. Notably, excessive convergence could affect the tension of the medial rectus muscle leading to AACE.

2.4

Malposition of extraocular muscle

Extraocular muscles are abnormally located in AACE patients. The distance from the insertion of medial rectus to the limbus is shorter in AACE patients, potentially causing an unbalance between convergence and divergence, subsequently resulting in esotropia.

2.5

Central nervous system dysfunction

A resting-state functional magnetic resonance imaging performed on AACE patients demonstrated abnormalities in central function.

2.6

Neurological diseases

AACE has been reported in Chiari I malformation, brain tumors and hydrocephalus.

A comprehensive neurological examination is recommended for patients exhibiting ocular symptoms (such as nystagmus, overaction of the superior oblique muscle and A pattern) and neurological signs (including headaches, poor motor coordination, papilledema and clumsiness) to identify potential neurological disorders for early diagnosis and effective treatment, thereby improving patient prognosis. Patients without neurological symptoms have a lower risk of underlying neurological disorders. However, careful monitoring is recommended for AACE patients without any neurological symptoms. For patients under the age of four, if there is no hyperopia or if esotropia does not improve after a full hyperopic prescription, the possibility of a neurological disorder should be considered. In pediatric AACE patients, key risk factors include neurological symptoms, a large deviation angle when viewing distant objects, recurrence after therapy and an older age of onset (over six years old). If any of these factors is present, a cranial magnetic resonance imaging examination should be performed.

4.1

Prism therapy

Prism glasses are effective in AACE patients with eye misalignment of less than 25 prism diopters (PD).

4.2

Botulinum toxin injection

Botulinum toxin injection includes administering botulinum toxin into the medial rectus muscle to effectively weaken its strength. Botulinum toxin injection is conducted through three methods: electromyography (EMG) guidance without conjunctival incision, direct injection without incision and EMG guidance, and injection with conjunctival incision and without EMG guidance. The conjunctival microincision injection technique enables simple and precise positioning of the extraocular muscle and is suitable for beginners. A review of studies based on the criteria of at least six months of follow-up, evaluating dose-dependent effects and achieving a 70 % success rate showed that the recommended dosage is 1.0–4.0 units for deviations ranging from 10 to 20 PD, 2.0–5.0 units for deviations between 21 and 40 PD, 4.0–6.0 units for deviations ranging from 41 to 60 PD and 7 units for deviations exceeding 60 PD.

The efficacy of botulinum toxin injection versus surgery remains controversial, with most studies reporting comparable outcomes for the two treatment approaches, particularly within the first six months of posttreatment. Botulinum toxin injections are particularly suitable for patients who opt out of surgery, patients with smaller angles of deviation and AACE patients with potential binocular vision. Measuring the strabismus angle two weeks post–botulinum toxin treatment can serve as a predictor for long-term treatment efficacy.

5.1

Preoperative prism adaptation test (PAT) or base-out recovery point

PAT is conducted before surgery to evaluate the latent strabismus angle thus reducing the risk of postoperative recurrence. Notably, PAT requires significant patient cooperation and time investment. For uncooperative patients, the preoperative base-out recovery point can be used as a surgical target. This approach offers a simpler and more efficient alternative to reveal the latent deviation angle.

5.2

Deviation angle

Patients should receive treatment after the deviation angle is stable.

5.3

Surgical dose

To avoid under-correction, a higher surgical dosage is recommended for AACE patients for both medial rectus recession and recession-resection procedures. A previous study established a surgical dosage calculation method for AACE patients. The findings showed that the dose-response relationship for medial rectus recession and lateral rectus resection surgery was 5.11 PD/mm and 2.51 PD/mm, respectively, for patients with a strabismus degree less than 30 PD. The additional dose-response relationship for lateral rectus recession was 5.48 PD/mm for correcting the deviation exceeding 30 PD in patients with a strabismus degree greater than 30 PD.

The timing of treatment initiation is a significant factor in the development of normal stereopsis. The possibility of decompensated monofixation syndrome should be considered if stereopsis is not resolved after treatment.

Notably, these consensus statements are not meant to be exhaustive. These recommendations should be viewed as a framework to guide treatment rather than definitive protocols because research is ongoing to explore additional clinical approaches for the treatment of this condition. Clinicians should apply their professional judgment and consider individual patient circumstances when making treatment decisions.