Dissociation between globe shape-induced rectus muscle pulley displacement and abduction limitation in patients aged 40 years and older with high myopic strabismus.

PURPOSE: We hypothesized that high myopia (HM)-induced globe deformation displaces rectus muscle (RM) pulleys, contributing to mild ocular motility restriction. This study investigated the effects of globe shape on RM pulley positions in older Japanese patients with acquired strabismus (AS) and mild motility restriction-defined as the ability to abduct both eyes beyond the midline.

METHODS

In this retrospective case series, 28 patients (mean age ± standard deviation: 61.2 ± 9.0 years) with adult-onset AS were included: 6 patients with (LAB group) and 22 patients without abduction limitation (NLAB group). In each subject, the eye with the longer axial length (AL ≥ 26 mm), measured using an AL measurement apparatus, was analyzed using magnetic resonance imaging (MRI). RM pulley positions relative to the globe center and equatorial diameter (ED) were measured; the ED-to-AL ratio (EAR) was calculated. We compared these parameters between groups and analyzed correlations of globe-shape factors (EAR, AL, and ED) with pulley positions and age.

RESULTS

No significant differences in EAR, AL, ED, or pulley positions were detected between LAB and NLAB groups, possibly owing to the limited sample size and group imbalance, in the analyzed eyes. However, as EAR decreased (prolate deformation), the superior rectus (SR) pulley (r = 0.68, P < 0.01) and inferior rectus (IR) pulley (r = 0.40, P = 0.03) significantly displaced nasally. AL (r = -0.52, P < 0.01) correlated with the horizontal SR pulley position. Furthermore, age significantly correlated with AL (r = 0.45, P = 0.02) and decrease in EAR (r = -0.41, P = 0.03).

CONCLUSIONS

In older Japanese patients with HM and AS, prolate globe deformation was associated with age and significantly correlated with SR and IR pulley positions. While the direct relationship between these structural changes and the clinical degree of mild abduction limitation requires further investigation in larger cohorts, EAR sensitively reflected age-related morphological shifts; thus, when used in conjunction with AL, EAR may represent a readily measurable MRI-based parameter associated with restrictive motility tendencies in strabismus with high myopia.