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Detection of Metallic Ocular Foreign Bodies With Handheld Sonography in a Porcine Model

Section of Emergency Ultrasound, Department of Emergency Medicine, Medical College of Georgia, Augusta, Georgia.

Address correspondence and reprint requests to Michael Blaivas, MD, RDMS, Department of Emergency Medicine, Medical College of Georgia, 1120 15th St, AF-2056, Augusta, GA 30912-4007. E-mail: blaivas{at}pyro.net

Objective. Eye conditions are common in emergency departments. Intraocular foreign bodies (IOFBs) are a frequent concern. Orbital computed tomography (CT) is traditionally used for evaluation. We sought to evaluate bedside ocular sonography for detecting metallic IOFBs. Methods. A pig model was chosen. A micrometer was used to create 3 precise metallic fragments: 0.012 x 0.012 x 0.012, 0.025 x 0.025 x 0.012, and 0.05 x 0.05 x 0.012 in. Individual eyes were randomized to the presence or absence of a foreign body. Randomization was also used to determine the specific size of any given IOFB. A standard 18-gauge spinal needle was used to puncture the sclera and introduce the IOFB into the vitreous. Each eye was then evaluated by 2 sonologists for the presence or absence of an IOFB. Results. A total of 28 eyes were used; 12 (43%) were randomized to no IOFB and 16 (57%) to the presence of an IOFB. Of the 16 eyes that received IOFBs, 8 (50%) were 0.012 x 0.012 x 0.012 in; 5 (31%) were 0.025 x 0.025 x 0.012 in; and 3 (19%) were 0.05 x 0.05 x 0.012 in. Sensitivity was 87.5% and specificity 95.8%. Positive predictive value (PPV) and negative predictive value (NPV) were 96.5% and 85.2%, respectively. Conclusions. Bedside sonography may identify the presence of metallic IOFBs. The PPV allows a high degree of certainty that an IOFB is actually present if seen and may negate the need for uninfused orbital CT. The NPV was 85.2%. Given the potential grave consequences of a missed IOFB, sonography cannot be used as the definitive test to rule out the presence of a metallic IOFB. In the presence of negative findings, further imaging is warranted.

Key Words: emergency medicine • emergency sonography • portable sonography • ocular foreign bodies • ocular sonography • sonography

Abbreviations: CT, computed tomography • IOFB, intraocular foreign body