The hazard of magnetic resonance (MR) imaging at low field strength (0.06 T) was examined by using both in vitro and in vivo animal experiments. Ferromagnetic fragments, 0.25-2.2 mm in diameter, were placed in vitreous humor obtained from excised cow eyes and in rabbit eyes. The magnetic field strength at which motion occurred was measured for each fragment size. Two types of motion, rotation and translation, were observed. The authors found that fragments that could not be seen on plain radiographs did not appear to move enough to be a significant ocular hazard during MR imaging at a field strength of 0.06 T.