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Ferromagnetism of intraocular foreign body causes unilateral blindness after MR study.

The rapid ascent of magnetic resonance (MR) imaging as an important tool in neurodiagnosis has been fueled primarily by its unparalleled sensitivity for lesion detection, even when compared with its predecessor, computed tomography (CT). The absence of ionizing radiation is another attractive feature of MR that has provided additional momentum for its rapid development. However, only recently, and on the eve of widespread distribution of this new technology, has significant attention been focused on the potential biologic hazards of MR. Among the risks to which MR patients may be exposed are included ferromagnetic forces that may be exerted on certain internal metal objects. Most patients harboring various types of surgically implanted aneurysm and hemostatic clips as well as other types of metallic hardware can be readily identified by history. Exclusion of individuals with a history of cerebral aneurysm treated by aneurysm clips from consider ation for MR eliminates the fearsome risk of a hemorrhagic event or other injury as a result of ferromagnetically induced motion of the metal clip. However, accurate recognition of the presence of small metallic foreign bodies such as an iron filing or shrapnel fragment, prior to consideration for MR, can be more problematic, even with preliminary CT, as we discov ered. A former sheet metal worker with a clinically occult intraocular metal fragment experienced a vitreous hemor rhage with resulting blindness during an MR examination. According to the Food and Drug Administration, this case represents the first reported instance of a serious complica tion related to induced ferromagnetism. Attention to the oc cupational history and a high index of suspicion may help avert this type of calamity in other patients similar to ours. The demonstrated ability of MR to cause serious injury as a result of ferromagnetism has important implications for a much larger group of potential MR candidates with surgically implanted metallic devices.