Intraocular Foreign Body

Recognition and Initial Evaluation

A classic setup for an intraocular foreign body (IOFB) is a construction or metal-work injury — grinding, hammering metal-on-metal, or a similar high-velocity mechanism — producing a small corneal wound with an irregular or peaked pupil. That combination should be triaged as globe penetration with a retained foreign body until imaging proves otherwise, since the entry wound itself can be deceptively small and easy to overlook.

The essential first step in evaluating a suspected IOFB is documenting visual acuity in both eyes. It is a critical baseline and prognostic measure that should be recorded before any manipulation or pressure-based testing that could risk further injury to a compromised globe. A relative afferent pupillary defect (RAPD), detected with the swinging flashlight test, is also an important part of the trauma pupillary exam — it flags asymmetric optic nerve or severe retinal dysfunction between the two eyes.

Imaging Workup

Thin-section computed tomography is the preferred initial imaging study for a suspected metallic IOFB. It is fast, widely available, and reliably detects metallic and most other radiopaque foreign bodies while avoiding the risk of magnetic movement associated with MRI. Thin, contiguous 0.5–1 mm axial cuts are recommended — they minimize partial-volume averaging and allow detection of small foreign bodies that thicker slices could miss entirely.

CT attenuation also helps characterize what the foreign body is made of. Glass is radiopaque and shows high attenuation comparable to metal on CT, unlike organic materials such as wood, which can be missed due to lower attenuation and can appear isodense to orbital fat. Once a metallic foreign body has been excluded, MRI becomes the imaging modality of choice for detecting an organic wood IOFB, since it better distinguishes organic material from surrounding soft tissue than CT does.

MRI is absolutely contraindicated whenever a metallic or ferromagnetic IOFB is suspected — a ferromagnetic fragment can move within the scanner's strong magnetic field and cause further intraocular damage. This is why CT, not MRI, is the default first study any time metal is on the differential.

B-scan ultrasonography has a role too, but technique matters in an open globe: it should be performed with minimal direct pressure on the globe. When ultrasound is necessary in a suspected open globe, extremely light probe contact through a closed lid is used to avoid expressing intraocular contents through the wound.

Exam Precautions in a Suspected Open Globe

Several routine exam maneuvers are deferred in a suspected open globe with a retained foreign body because they risk extruding intraocular contents through the wound. Gonioscopy is generally avoided for exactly this reason — the mirrored lens placed directly on the eye can express contents through an open wound, so it is deferred until the globe is confirmed intact or surgically closed. The same pressure-avoidance logic applies to applanation tonometry and any other test that touches or compresses the globe.

Extraction Technique and Timing

For a ferromagnetic IOFB (iron, steel), intraocular magnet extraction is generally the preferred technique. It allows atraumatic capture and removal with minimal manipulation, reducing the risk of further retinal or vitreous damage compared to grasping the fragment with forceps.

Foreign bodies lodged in the posterior segment are removed via pars plana vitrectomy, which allows controlled visualization and removal while managing associated vitreous hemorrhage, retinal breaks, and traction — minimizing further intraoperative retinal trauma. When the IOFB has traversed and damaged the crystalline lens on its way to the posterior segment, a combined lensectomy and pars plana vitrectomy is typically performed: it removes the damaged, often cataractous lens and provides surgical access for foreign body retrieval and posterior segment repair in a single procedure.

Timing matters as much as technique. To minimize the risk of post-traumatic endophthalmitis, surgical removal of an IOFB should ideally occur within 24 hours of injury. Early removal, combined with prompt systemic and intravitreal antibiotics, significantly reduces endophthalmitis risk — especially with organically contaminated foreign bodies.

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