Detection of metallic ocular foreign bodies with handheld sonography in a porcine model

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.

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.

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.

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.