Purpose: To quantitatively analyze the shape of eyes with high myopia and provide assistance for posterior scleral reinforcement (PSR) using high-resolution three-dimensional (3D) magnetic resonance imaging (MRI). Method: In all, 260 eyes of 134 patients with high myopia were assessed in this study; 120 emmetropic volunteers were enrolled as a control group. The subjects were examined using 3D T2-weighted CUBE sequences. Results: The eyeballs' axial, horizontal, and vertical lengths were longer and their volume was larger in the subjects with high myopia than in those with emmetropia. The sites of the four recti and optic nerve attachment to the eye were clearly seen on 3D MRI, and the geometric information could be quantified for PSR preparation. The scleral strip was revealed by 3D MRI after surgery. Conclusions: 3D MRI can quantitatively analyze the shape of eyes with high myopia. 3D MRI examination might be necessary before and after PSR for preoperative preparation and postoperative assessment.