The onset of acute acquired comitant esotropia (AACE) is related to long-term near work, according to a study published in Clinical and Experimental Optometry.
The study describes the clinical characteristics and etiology of AACE based on medical records of 51 patients with AACE as well as their age, occupation, daily average time spent on near work, angle of deviation, and refractive error.
The study found that the age of onset ranged from 8 years to 55 years, with 76.5% (n=39) of participants between the ages of 12 years and 36 years. Participants with myopia consisted of 82.4% (n=42) of the sample. During near fixation, the angle of deviation was 20∆ (12∆ to 35∆), and during distance fixation, 25∆ (18∆ to 40∆), and this difference was statistically significant (P <.001). On average, the daily time of near work before onset was 9.0 hours (8.0 to 10.0 hours), and 68.6% (n=35) of participants, whose occupations required use of electronics for long periods, spent more than 8 hours performing near work. No correlation was found between angle of deviation and duration of near work (P >.05). Following treatment, diplopia resolved in 47 cases, and the angle of deviation was 0∆ (0∆ to 5∆) during near fixation and 0∆ (0Δ to 3Δ) during distance fixation.
The researchers explain that AACE is classified into 3 types, 1 of which — the Bielschowsky type — is caused by myopia, and it occurs mostly in adolescents and adults.
“The pathogenesis is related to uncorrected myopia,” the study notes. “Near work induces excessive convergence, and an increase in the tension of the medial rectus muscle, resulting in an imbalance in the strength between the convergence and divergence of the eyes, finally resulting in esotropia.”
Furthermore, the researchers suggest a physiological mechanism that may contribute to their finding a difference between the angle of deviation at distance and at near fixation.
“The reason may be that patients stare at objects at close distances for a long time, resulting in increasing tension of the medial rectus muscle and decreasing the use of the lateral rectus muscle,” according to the research.
Meng Y, Hu X, Huang X, et al. Clinical characteristics and aetiology of acute acquired comitant esotropia. Clin Exp Optom. Published online April 29, 2021. doi:10.1080/08164622.2021