Objective To investigate the feasibility of using magnetic resonance imaging (MRI) to measure the visual axis length in silicone oil filled eyeballs. Methods Thirty-two silicone oil-filled eyes of 32 patients were studied. The antesilicone oil spaces (ASS) and retro-silicone oil spaces (RSS) on the visual axis was measured on the cross-sectional T1 weighted images (T1 WI) and T2WI, the length of the visual axis was measured on the fatsuppressed T2WI. The length of the visual axis was the distance from the corneal vertex to the macular fovea, and it was also measured by A-mode ultrasound in sitting position with different ultrasonic velocity. The postoil gap was also measured by A-mode ultrasound in supine position. Results Compared with the signal of the contralateral vitreous body, the silicone oil signal was higher on T1WI images, lower on T2WI images. After fat suppression, the silicone oil signal and chemical shift artifact were reduced. There were different levels of ASS and RSS in the vitreous cavity of all 32 cases, the RSS depth was (2.47plusmn;1.31) mm on average by MRI. However, RSS was detected in only 56.25% (18 cases)eyeballs by A-mode ultrasound. The visual axis length of silicone oil-filled eyes was (23.52plusmn;4.67) mm by MRI, and (20.57plusmn;5.32) mm by A-mode ultrasound in sitting position. The differences between two measurements was statistically significant (t=30.17, P＜0.05). Conclusions In addition to A-mode ultrasound, MRI might be another effective method to detect RSS and ASS, and to measure the axial length of silicone oil-filled eyes.