Corneal Trauma & Foreign Bodies

Presentation & Evaluation

An uncomplicated corneal foreign body classically presents with a triad: foreign body sensation, reflex tearing, and photophobia. All three trace back to corneal nerve irritation and the ciliary spasm it provokes. The first step in evaluating any suspected corneal foreign body or abrasion is slit-lamp biomicroscopy with fluorescein staining, which lets the examiner visualize the foreign body directly, judge how deep it sits, and identify any associated epithelial defect. Jumping straight to empiric treatment or reflex referral, without examining the eye at the slit lamp first, skips the step that actually determines management.

Fluorescein pools in areas where the corneal epithelium has been disrupted; under cobalt blue illumination it fluoresces bright green, sharply outlining abrasions, ulcers, or the track a foreign body leaves behind. The pattern of uptake is itself a clue. A curvilinear or linear streak often points to a foreign body dragged across the cornea by the lid, such as a contact lens edge or a trapped particle, rather than a single point of impact.

Foreign Body Removal

A superficial, loosely adherent foreign body is best removed at the slit lamp, under topical anesthesia and magnification, using a fine needle or a dedicated foreign body spud. This precise, controlled approach minimizes damage to the surrounding cornea. Vigorous irrigation or rubbing with a cotton-tipped applicator is not an adequate substitute for direct, visualized removal.

Rust Ring Removal

Metallic foreign bodies frequently leave a residual rust ring of iron deposited in the stroma after the fragment itself is removed. A rotating ophthalmic burr, commonly known by the brand name Alger brush, is used to gently debride this residual iron. Complete same-day removal is not always necessary, or even wise: when a rust ring is deeply embedded and cannot be fully cleared without risking excessive stromal damage, the better course is to leave the residual ring alone and have the patient return in 24–48 hours. By then the ring has typically softened enough to allow safer, more complete removal, and forcing total clearance in a single aggressive pass risks unnecessary tissue loss.

Foreign bodies involving plant or vegetable matter deserve special caution. Organic material can introduce fungal spores directly into the cornea, so a vegetative injury should raise suspicion for fungal keratitis, especially if the eye worsens despite standard antibacterial treatment.

Subtarsal Foreign Bodies

A particle trapped under the upper eyelid produces a distinctive fluorescein pattern: multiple fine, vertical linear corneal abrasions, caused by the foreign body dragging across the cornea with every blink. That pattern should prompt eversion of the upper eyelid, or "flipping the lid," to search directly for the foreign body. It will not be visible or reachable by examining the cornea alone.

Management After Removal

After removal, a topical broad-spectrum antibiotic is routinely prescribed to reduce the risk of secondary bacterial infection while the epithelial defect heals. A cycloplegic agent is often added to relieve photophobia: corneal injury triggers reflex ciliary muscle spasm, and cycloplegia relaxes both the ciliary muscle and the iris sphincter for real symptomatic relief.

Two management points apply to specific patient groups. Contact lens wearers who sustain a corneal foreign body or abrasion should generally not be patched. Contact lens wearers, along with anyone with an organic or contaminated foreign body, are at elevated risk of Pseudomonas keratitis or other gram-negative infection, and the warm, moist, occlusive environment under a patch favors bacterial proliferation. Topical anesthetic drops should never be sent home with a patient for self-administered pain control, either. Repeated unsupervised use impairs epithelial healing and can itself cause toxic keratopathy; anesthetic drops are strictly an in-office diagnostic and procedural tool. (See Corneal Anesthetic Abuse & Neurotrophic Disease for the full clinical picture of what happens when this rule is violated.)

Retained Intraocular Foreign Bodies

The mechanism of injury matters as much as the exam findings. A high-velocity metal-on-metal injury, hammering metal on metal is the classic example, carries a real risk of an occult fragment penetrating the globe even when the external exam looks reassuring. That history alone should prompt imaging; a normal-looking eye is not reassurance enough to skip it. When an occult, metallic intraocular foreign body is suspected, thin-cut computed tomography of the orbit without contrast is the imaging study of choice. Magnetic resonance imaging is contraindicated in this setting: its magnetic field can pull a ferrous foreign body and cause further intraocular injury.

Siderosis Bulbi and Chalcosis

A retained intraocular foreign body that goes undetected or unremoved can produce delayed toxic reactions specific to its metal content. Siderosis bulbi results from iron deposition into ocular tissues from a retained ferrous, or iron-containing, foreign body, leading to retinal toxicity, cataract, and heterochromia if the fragment isn't removed. Chalcosis is the copper-containing counterpart: a retained copper foreign body causes copper deposition classically associated with a sunflower cataract, a Kayser-Fleischer-like corneal ring, and its own pattern of retinal toxicity. Both are reasons a suspected retained IOFB is a genuine urgency and not just a foreign-body-sensation complaint. The fragment itself keeps causing damage for as long as it stays in the eye.

Seidel Sign & Open Globe Injury

The Seidel test uses the same fluorescein staining already central to routine foreign body evaluation, but asks a different question: is there a full-thickness wound leaking aqueous? A positive Seidel sign appears as a stream of diluted, lighter-colored fluid within the concentrated orange-green dye under cobalt blue light. Aqueous humor leaking through the wound washes out and dilutes the fluorescein at its edge, producing a visible streaming pattern. A positive Seidel sign confirms an open globe injury and mandates urgent surgical repair.

Once an open globe is suspected, whether from history, exam, or a positive Seidel sign, the exam itself changes. Measuring intraocular pressure with a tonometer is contraindicated: applanation or contact tonometry applies external pressure directly to the globe and risks extruding intraocular contents through the open wound. Fluorescein staining, placement of a rigid protective shield, and keeping the head of the bed elevated at rest all remain safe and appropriate. When a full-thickness laceration with a suspected intraocular foreign body needs imaging, thin-cut CT without contrast is still preferred; contact B-scan ultrasound is avoided because the probe itself would press on an already compromised globe.

Not every full-thickness corneal wound needs the operating room. A very small laceration, under about 2 mm, that is well-apposed and not actively leaking, with a formed anterior chamber and no iris or vitreous prolapsed through the wound, can often be managed with cyanoacrylate tissue adhesive and a bandage contact lens instead of sutures. A laceration over that size, a wound that is gaping or still leaking, or one with uveal tissue prolapse still needs sutured repair in the operating room. If the adhesive fails to achieve a watertight seal, the next step is suturing, not a second attempt at glue.

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