A Sneaky Sliver of Metal

A 41-year-old patient came in after “something bounced off” his eye while he was hammering without wearing safety glasses.

His VA was 20/20-1 with mild pain. A slender Seidel-negative corneal wound and 2+ cells were also noted. Further evaluation revealed a small superonasal iris hole, vitreous hemorrhage, and a bubble-like opacity with retinal whitening. Imaging confirmed a metallic intraocular foreign body (IOFB) in the retina (Figure), which was removed with vitrectomy.

In addition to traumatic cataract, iron from a metallic IOFB can quietly lead to ocular siderosis,^1,2 a slow poisoning of the eye whereby iron leaches from the fragment and deposits in the iris, lens, trabecular meshwork, and retina. Over time, siderosis can lead to heterochromia, tonic mydriasis, cataract, secondary glaucoma, and/or retinal dysfunction. Once advanced, the damage is often irreversible, so early suspicion and removal of the IOFB are critical.^1,2

WHAT TO LOOK FOR

IOFBs can be challenging to detect. In a multicenter series of delayed or initially missed IOFBs, each eye had a self-sealed, Seidel-negative wound.¹ Although most patients had a VA of 20/30 or better after treatment, more than a quarter already had siderosis at diagnosis.^1,2 It’s also worth noting that IOFBs were just as likely to sit in the iris/anterior chamber or lens as in the vitreous or retina.²

Patient history is critical; metal-on-metal activity (ie, hammering, grinding, chiseling, and nail or screw impact) should automatically raise suspicion for an IOFB, regardless of visual acuity or Seidel examination, as the high velocity allows for penetration through ocular tissues. At the slit lamp, look for subtle signs such as a tiny paracentral or peripheral self-sealing wound, iris transillumination defect or hole, irregular or peaked pupil, or a focal spoke-like lens opacity along the suspected path.¹ Posteriorly, disproportionate vitreous hemorrhage, localized retinal whitening, or a small “bubble” on or near the retina should raise suspicion for an IOFB, as opposed to commotio or traumatic vitritis.² Urgent referral to a retina or cornea/anterior segment specialist, depending on the location, is warranted if there is suspicion of an IOFB.

IMAGING

Thin-slice CT of the orbits often works well in such cases if needed, as it detects most IOFBs and has been shown to outperform clinical examination or B-scan alone.² B-scan is still valuable in cases of vitreous hemorrhage or when CT is equivocal, and ultrasound biomicroscopy can be useful when angle or ciliary body involvement is suspected.² MRI is not a viable option when metal is involved.

THE TAKEAWAY

When patient history and clinical signs do not align with a diagnosis of simple abrasion, it is often best to treat the eye as if there is an IOFB until you are able to rule it out.

Acknowledgements: Dr. Henderson would like to thank Griff Christenson, OD, for his assistance with this case.