Retrobulbar microvascular and biomechanical changes associated with axial elongation in myopic eyes

This study aimed to investigate retrobulbar biomechanical and microvascular changes associated with increasing axial length in myopic eyes using shear wave elastography and a quantitative vascularity index. In this prospective cross-sectional study, 99 eyes from 99 adults were classified into three groups according to axial length: <24.00 mm (Group 1), 24.00-25.99 mm (Group 2), and ≥ 26.00 mm (Group 3). All participants underwent comprehensive ophthalmologic and ultrasonographic evaluations. Shear wave elastography was used to quantify the stiffness of the optic nerve and adjacent retrobulbar fat tissue. Retrobulbar microvascularity was assessed using ultra-microangiography, with color pixel percentage measured as a vascularity index. No significant differences in tissue stiffness were observed among axial length groups (all p > 0.05). However, the vascularity index differed significantly between groups (p = 0.026) and remained independently associated with axial length after adjusting for age and sex (p = 0.041), suggesting progressive reduction in retrobulbar microvascularity, reflected by lower vascularity index values, with increasing axial elongation. Optic nerve diameter significantly decreased with increasing axial length (p = 0.010). These findings indicate that axial elongation in myopic eyes is associated with significant retrobulbar microvascular changes without corresponding alterations in tissue stiffness.