Abstract: Objective To analyze magnetic resonance imaging data of the extraocular muscles in convergence. Design Experimental study. Participants Eight normal subjects aged (27.4±3.1) years. Methods Eight normal subjects, non-convergence state, asymmetrical convergence: a total amount of 20△ base-out prism was placement in front of the right eye or the left eye; symmetrical convergence: 10△ base-out prism was placement in front of both eyes. Extraocular muscles (EOMs) paths were evaluated by axial, coronal and sagittal MRI scans during the subject focus to a target at a distance of 5 m from the eye. Main Outcome Measures In convergence, the contractile changes of the EOMs and the converging eye rotated degrees. Results In asymmetrical convergence, the converging eye lateral rectus (LR) muscles exhibited significant relaxational thinning compared with the non-convergence eye (cross-sectional area were 0.4710±0.1077 and 0.5155±0.1168 cm2，P=0.037), while the other EOMs did not showed significant contractile changes. The converging eye rotated nasally 11.03±1.44°, the aligned eye rotated nasally 1.40±0.46°, and the converging eye showed 1.0° intorsion of the rectus pulley array. In symmetrical convergence, the eye rotated nasally 5.26±1.15°; there were no significant contractile changes in the cross sections of the EOMs. Conclusion The converging eye LR muscles exhibited large contractile cross-section changes. The significant changes of the eye rotation associated with the asymmetrical convergence and symmetrical convergence. (Ophthalmol CHN, 2014, 23: 251-255)

Key words: magnetic resonance imaging, extraocular muscles, convergence, asymmetrical