Association between crystalline lens thickness and intermittent exotropia in children: a cross-sectional observational clinical study.

Abstract

Purpose: To investigate the relationship between crystalline lens thickness (LT) and subtypes of intermittent exotropia (IXT) in children, focusing on ocular biometry and accommodation characteristics.

Methods: This cross-sectional study included 501 children aged from 8 to 12 years: 122 with orthophoria (Group A) and 379 with IXT, which were further categorized into basic type (Group B, n = 254), convergence insufficiency (CI) type (Group C, n = 92), and divergence excess (DE) type (Group D, n = 33). Evaluation of strabismus was measured after diagnostic occlusion. Cycloplegic refraction and assessments of accommodation and convergence functions were performed. All children were examined with Lenstar LS-900 with fixation at non-accommodative target monocularly and ocular biometric parameters including axial length (AL), mean keratometry (Km), central corneal thickness (CCT), LT and aqueous depth (AD) were recorded. Regression analyses were performed to evaluate associations among groups.

Results: The basic type was the most prevalent IXT subtype (67.0%), followed by CI (24.3%) and DE (8.7%). The CI group exhibited greater binocular LT (P = .002) and lower accommodative convergence-to-accommodation (AC/A) ratio compared to the basic type (P = 0.016). Compared to orthophoric controls, the basic IXT group showed greater accommodative amplitude (AMP) (P = 0.004), reduced accommodation lag (P = 0.006), and more distant near point of convergence (NPC) (P < 0.001). Both univariate and multivariate logistic regression analyses indicated that the CI IXT was associated with greater LT (P = 0.006) and lower AC/A ratio (P = 0.007) compared to basic IXT. Basic IXT was correlated with greater AMP (P < 0.001), reduced lag of accommodation (P = 0.002) and more distant NPC (P = 0.003) compared to controls.

Conclusions: Increased LT and lower AC/A ratio were significantly associated with the CI subtype of IXT in children. The basic type is characterized by greater AMP, reduced accommodation lag, and more distant NPC compared to orthophoric controls. These findings could serve as valuable clinical markers for managing IXT, and contribute to a deeper understanding of the pathophysiology of types of IXT.