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  • Identifying Intraocular Foreign Bodies

    By Unni K. Nair, MD, Anthony J. Aldave, MD, and Emmett T. Cunningham Jr. MD, PHD, MPH
    Edited by Ingrid U. Scott, MD, MPH, and Sharon Fekrat, MD
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    This article is from October 2007 and may contain outdated material.

    Ocular trauma is a major cause of blindness worldwide. In the United States, it is estimated that up to 2.4 million ocular injuries occur each year. Retained intraocular foreign bodies (IOFBs) represent an important finding following ocular trauma. The identification of IOFBs can be quite challenging clinically. Retained foreign bodies can cause infection and inflammation in the affected eye even years after the initial insult. Several imaging modalities are currently available to aid in screening for the presence of retained IOFBs—each with its own advantages and limitations.

    Current Imaging Modalities

    Computed tomography (CT) is currently considered the “gold standard” for the detection, localization and characterization of both metallic and nonmetallic IOFBs. Traditionally, axial sections separated by 3 to 5 mm have been utilized as an initial screening study for IOFBs. Spiral CT is a newer advancement that has helped overcome some of the limitations of conventional CT, including motion artifacts and long examination times.1But because studies comparing the detection of steel IOFBs measuring 0.06 mm3 or larger have shown no difference in sensitivity between spiral and conventional scanning CT,2,3 either imaging modality is probably adequate for detection of all but the smallest of IOFBs.

    Standard B-scan ultrasonography can also be used to detect metallic IOFBs, but the sensitivity is user-dependent. In addition, it is important to note that a small amount of intraocular air can occasionally be mistaken for an IOFB and that contact ultrasonography is contraindicated in globes suspected of rupture.

    Ultrasound biomicroscopy (UBM) has been examined as an adjunct to CT scanning. Deramo and colleagues demonstrated the usefulness of UBM in the detection of suspected IOFB in nine eyes, including two eyes in which CT scanning failed to visualize wooden and metallic foreign bodies. UBM was found to be especially helpful in the management of small, nonmetallic IOFBs located in or near the anterior chamber.4

    Plain film x-rays alone may be used as a screening modality for IOFBs, but of all the imaging techniques, x-rays are most likely to yield an equivocal result. Etherington and colleagues conducted a retrospective review to characterize the usefulness of both CT scanning and plain film x-rays as screening modalities for IOFBs. Their study revealed that if an IOFB could be seen on a plain film x-ray, then 6-mm CT cuts would be sufficient to detect and localize the IOFB. Conversely, when IOFBs were not able to be seen on plain films, 3-mm CT cuts were necessary to ensure accurate localization.5

    Magnetic resonance imaging (MRI) is contraindicated in the detection of suspected metallic IOFBs because the associated electromagnetic field can cause foreign body migration, potentially damaging intraocular tissues. An MRI is also more susceptible to motion artifact than other imaging modalities. MRI may be considered when there is a strong suspicion of a nonmetallic foreign body not seen with CT scanning or B-scan ultrasonography.

    Workup

    A complete history should be taken and ocular examination performed on all patients suspected of having a retained IOFB. The history should include specific questions regarding occupation, prior eye trauma, the mechanism of the current injury and whether eye protection was worn at the time of the injury. Physical examination should look specifically for direct or indirect evidence of an open-globe injury, including vitreous hemorrhage and/or streaming to a perforation site. In long-standing IOFBs, a characteristic pigment dusting may be present on the anterior lens capsule. If a globe is ruptured, systemic antibiotics and tetanus prophylaxis should be administered, and further examination should be deferred until surgical exploration can be conducted. When available, spiral CT scanning utilizing 3-mm axial and coronal cuts through the orbit should be obtained as a first-line study; conventional CT scanning with 3-mm cuts is an acceptable alternative. Plain film x-rays and B-scan ultrasonography are convenient to obtain and may be used as adjuncts to CT scanning, but are generally less sensitive and so “negative” results should be interpreted with caution.

    Case Presentation

    A 32-year-old man presented to his local ophthalmologist complaining of acute onset of redness, discomfort and reduced visual acuity in his left eye. Past ocular history was remarkable for a corneal metallic foreign body that was removed from his left eye three years prior to presentation. Past medical and surgical histories were unremarkable, and a review of systems was noncontributory. The patient was diagnosed with nongranulomatous anterior uveitis and treated with a cycloplegic/mydriatic agent, topical prednisolone acetate 1 percent, and, subsequently, a posterior sub-Tenon’s injection of 40 mg of triamcinolone acetonide. After no improvement, the patient was then referred for further evaluation.

    On presentation, BCVA was 20/20 in his right eye and 20/40 in his left, and IOP was 12 mmHg and 10 mmHg, respectively. There was no afferent pupillary defect. Corneal sensation was normal, and symmetric and anterior segment examination revealed bilateral well-healed corneal scars consistent with his history of prior corneal foreign body removal. The left eye had fine keratic precipitates on the inferior corneal endothelium, 2+ cells and trace flare in the anterior chamber and fine pigment dusting on the anterior lens capsule. Posterior segment examination of the left eye revealed scattered cells in the anterior vitreous, mild optic disc edema, patchy vascular sheathing and inferior vitreous opacities. Laboratory testing revealed a normal chest x-ray, a negative RPR, a negative FTA-ABS, a normal ESR, and normal serum ACE and lysozyme levels. Fluorescein angiography showed late leakage from the optic nerve and confirmed the presence of patchy vasculitis. B-scan ultrasonography showed no IOFB. Given the presence of characteristic pigment dusting on the anterior lens capsule, strong suspicion remained for an IOFB. A CT scan of the orbits was obtained and revealed a metallic IOFB just behind the inferior iris in the left eye. Pars plana vitrectomy was performed with removal of the IOFB. The ocular inflammation resolved rapidly. At follow-up examination five months after presentation, a posterior subcapsular cataract had developed but there were no signs of active inflammation.

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    1 Dass, A. B. et al. Ophthalmology 2001;108(12):2326–2328.

    2 Woodcock, M. G. L. et al. Ophthalmology 2006;113(12):2262–2269.

    3 Chacko, J. G. et al. Ophthalmology 1997;104(2):319–323.

    4 Deramo, V. A. et al. Trans Am Ophthalmol Soc 1998;96:355–365; discussion 365–367.

    5 Etherington, R. J. and M. D. Hourihan. Clin Radiol 1989;40(6):610–614.

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    Dr. Nair is an ophthalmology resident at California Pacific Medical Center in San Francisco. Dr. Aldave is an associate professor of ophthalmology at the University of California, Los Angeles, where he is director of the cornea service. Dr. Cunningham is director of the uveitis service at CPMC and an adjunct clinical professor of ophthalmology at Stanford. He thanks the San Francisco Retinal Foundation and the Pacific Vision Foundation for their support.