Rate of Divergence Insufficiency is Rising, 40-Year Clinic Study Reports

Until now, theories regarding the pathogenesis of divergence insufficiency (DI) in patients with acquired esotropia include eyeglasses underpowered for near work and sagging eye syndrome. An investigation from Wilmer Eye Institute found the incidence of DI is increasing, and progressive addition lenses (PALs) may play a part.

Investigators employed a uniform DI criterion for all esotropia patients of a single clinical practice from 1978 to 2018, with resulting data published in the Journal of The American Association for Pediatric Ophthalmology and Strabismus. “Our study found the use of PALs to be a risk factor for DI after controlling for age,” the analysis notes. From 1978 to 1998, 11.8% of patients with acquired esotropia presented with DI, but from 1999 to 2018, this percentage rose to 29.4% (P <.001).

In comparison, from 1978 to 1998, 5.3% of those with acquired esotropia wore PALS, but between 1999 to 2018, this figure rose to 16.8% (P <.001), according to the study. The analysis found increased odds of developing DI with the use of PALs, and 22.1% of patients with DI used progressives, compared with 11.4% of participants without DI (P <.001).

Of 646 acquired esotropia patients during the 41-year period, 256 were grouped as acquired esotropia without DI, and 390 classified as having or not having DI based on distance esotropia at ≥5Δ difference from near esotropia. The analysis showed an “accelerating (nonlinear) increase” in the amount of esotropia patients with DI through the years. In 10-year age groups, DI incidence rose in each group with an exception of patients 70 to 80 years of age. The age at which patients presented with acquired esotropia including DI increased until 75 years of age, then trended lower. 

Notably, researchers report a delay from patients’ first symptoms to eventually seeking care, compared with other esotropia-related conditions (P <.001). This may illustrate gradual evolution of the disorder — patients seeing double at distance, but having acceptable vision in close work. Other patients with acquired esotropia may have more immediate visual disturbances at far and near.

Investigators speculate that if DI was caused by orbital connective tissue deterioration alone, it would not completely account for the rising occurrence of DI, adjusted for age. Instead, other factors are likely involved. Individuals with under-corrected near vision, or not gazing to the bottom-most part of PALs may try harder to accommodate in near work. Further, for young adults, escalating use of smartphones and tablets may cause change in extraocular muscles, with shortening of the medial rectus muscle.

The retrospective nature of this analysis represents a limitation. Its strength is presenting new data regarding how current technology may affect DI. “These findings, combined with the occurrence of DI in young patients engaging in prolonged near work, support the concept that chronically increased convergence tonus, with subsequent shortening of medial rectus muscles relative to lateral rectus muscles, can be one of the mechanisms contributing to the etiology and/or evolution of many cases of DI,” the investigation suggests.

Reference

Chen X, Marsh JD, Zafar S, et al. Increasing incidence and risk factors for divergence insufficiency esotropia.J AAPOS. Published online September 24, 2021. . doi:10.1016/j.jaapos.2021.05.013