Diminished ciliary muscle movement on accommodation in myopia.

The contribution of ciliary muscle to the development and progression of myopia has been addressed. A thickened ciliary muscle in myopia has been speculated as an internal equatorial growth restriction, possibly a matter of hypertrophy with potentially poor contractility, which may result in the development and progression of myopia. In this preliminary study, we evaluated the interrelationship of ciliary muscle characteristics and myopia in 31 volunteers (aged 19-35), via ultrasound biomicroscope (UBM), with eyes focused on far and near targets. Univariate and multivariate regression analysis (using stepwise variable selection) were employed to analyze the relationship between axial length/refractive error and various parameters of ciliary muscle (CM)-cross-sectional area (CMA); length from scleral (CMLs) and vitreous (CMLv) aspects; thickness at 1.0 mm (CMT1), 2.0 mm (CMT2), and 3.0 mm (CMT3) posterior to scleral spur; maximum thickness (CMTm); and apical angle. The impact on accommodation of changes (Δ) in above parameters and of centroid variations was subsequently assessed. In a univariate analysis, axial length showed positive relationship with CMLs (r = 0.454, p = 0.017) and CMT3 (r = 0.460, p = 0.018), and negative relationship with ΔCMTm (r = -0.501, p = 0.008) and Δapical angle (r = -0.400, p = 0.039). Multivariate regression analysis showed that ΔCMTm (β = -0.506, p = 0.008) was independently related with axial length. A negative correlation between CMTm and ΔCMTm was also observed (r = -0.432, p = 0.024). These results suggest that accentuated ciliary muscle thickness, suggesting muscular hypertrophy, may account for the inherent dysfunction in myopia. Further studies are necessary to confirm these preliminary observations and hypotheses.