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Summary Table

Category	Details
Risk Factors	Welders, grinders, metalworkers, carpenters, construction workers, agricultural workers, children playing in sandy or windy environments, lack of protective eyewear, hammering metal on metal
Etiology	Metallic fragments (most common occupational), wood splinters, glass, plastic, organic debris (sand, dirt, plant matter), insect parts, displaced eyelashes
Patient Presentation	Acute unilateral foreign body sensation, tearing (epiphora), photophobia, eye pain, blurred vision, blepharospasm, conjunctival redness
Classic Physical Exam	Visible particle on cornea or conjunctiva, conjunctival injection, fluorescein uptake, rust ring around metallic foreign body, vertical linear corneal abrasions suggesting subtarsal foreign body, normal pupillary response
Key Diagnostic Results	Visual acuity (mandatory first step), slit lamp examination with fluorescein staining, Seidel test to rule out globe perforation, CT scan of orbit (axial and coronal, 1 mm cuts) when intraocular foreign body is suspected
Management	Topical anesthetic, copious saline irrigation, removal with moistened cotton applicator (conjunctival) or 25 to 27 gauge needle / eye spud under slit lamp (corneal), topical antibiotic prophylaxis, tetanus update for organic material, urgent ophthalmology referral if deep, central, or suspected penetrating injury
Keywords	"Welder without goggles", "grinding metal", "hammering metal on metal", "rust ring", "foreign body sensation", "vertical linear scratches", "Seidel positive"

1. Pathophysiology

The eye possesses several protective mechanisms (eyelids, lashes, blink reflex, tear film), but high-velocity particles or sustained low-speed contact can overwhelm these defenses. The pathophysiology depends on the location, velocity, and composition of the offending material.

When a particle lodges on the bulbar or palpebral conjunctiva, it irritates richly innervated mucosa via the ophthalmic branch of the trigeminal nerve, producing the hallmark foreign body sensation and reflex tearing. With each blink, the trapped particle may abrade the corneal epithelium, classically producing vertical linear corneal abrasions when lodged under the upper tarsal plate. This pattern is a major test-writer favorite because it mandates eyelid eversion during examination.

A corneal foreign body disrupts the corneal epithelium, exposing the highly innervated Bowman layer and stroma. This explains the disproportionate pain, photophobia, and reflex blepharospasm. The corneal epithelium normally heals within 24 to 72 hours, but retained material prevents re-epithelialization and serves as a nidus for bacterial keratitis, particularly with organic matter (Pseudomonas, fungi).

Metallic foreign bodies, especially iron-containing particles, undergo oxidation within hours and form a rust ring in the surrounding stroma. This ring is toxic to keratocytes and impairs healing if not removed. Copper causes severe sterile inflammation (chalcosis), and organic material carries a high risk of fungal infection.

The most dangerous scenario is an intraocular foreign body, typically following high-velocity injury (hammering, grinding, explosions). The particle penetrates the cornea or sclera, leading to open globe injury, vitreous hemorrhage, retinal damage, and a high risk of endophthalmitis and sympathetic ophthalmia. The classic vignette pairs an occupational exposure with decreased visual acuity, peaked or teardrop pupil, hyphema, or a positive Seidel test (aqueous streaming through the cornea after fluorescein application).

2. Classification of Clinical Manifestation

Classification	Location	Typical Presentation	Severity
Superficial conjunctival	Bulbar or palpebral conjunctiva	Foreign body sensation, tearing, mild redness, no visual loss	Mild
Subtarsal	Under upper eyelid	Severe foreign body sensation, vertical linear corneal abrasions, requires lid eversion	Mild to moderate
Superficial corneal	Anterior corneal epithelium	Pain, photophobia, fluorescein uptake, visible particle, possible rust ring	Moderate
Deep corneal stromal	Embedded in stroma, near Descemet membrane	Risk of perforation during removal, central location threatens vision	Moderate to severe
Intraocular foreign body	Penetrated globe (anterior chamber, lens, vitreous, retina)	Decreased acuity, peaked pupil, hyphema, Seidel positive, hypotony	Severe (vision-threatening)
Orbital (extraocular) foreign body	Behind globe, within orbital tissues	Proptosis, restricted motility, possible retained organic material	Severe (infection risk)

3. Diagnostic Workup

Test	Purpose	Findings
Visual acuity (Snellen chart)	First step in any ocular complaint, medicolegal documentation	Baseline assessment, decreased acuity raises suspicion for deeper injury
External inspection and lid eversion	Locate foreign body, check tarsal conjunctiva	Visible particle, conjunctival injection
Slit lamp biomicroscopy with fluorescein	Best initial test for localization	Particle visualization, epithelial defect, rust ring, anterior chamber inflammation
Seidel test	Rule out globe perforation	Aqueous streaming through cornea = positive (open globe)
CT scan of orbit (thin cuts)	Suspected intraocular or orbital foreign body	Confirmatory for radiopaque material (metal, glass)
B-scan ultrasonography	Posterior segment evaluation if media opaque	Avoid if open globe is suspected
MRI	Contraindicated if metallic foreign body is suspected	Risk of magnetic displacement and intraocular damage

The first action in every ocular complaint is to document visual acuity in both eyes, even before applying anesthetic. This is non-negotiable on examinations; skipping it is the most common procedural error tested. Use a Snellen chart, a near card, or finger counting as appropriate, and record results before any intervention.

Next, perform external inspection under good light, followed by eyelid eversion, particularly the upper lid. Many trapped particles sit on the superior tarsal conjunctiva, and a vignette describing vertical linear corneal abrasions is a strong clue that a subtarsal foreign body has been overlooked.

Apply topical anesthetic (tetracaine 0.5% or proparacaine 0.5%) to allow comfortable examination. The best initial test is slit lamp biomicroscopy with fluorescein staining. Fluorescein highlights any epithelial defect under cobalt blue light, reveals the foreign body, and helps assess depth. Inspect for a rust ring, anterior chamber cells, hyphema, and irregular pupil shape.

Always perform a Seidel test when a penetrating injury is plausible. Place a fluorescein strip on the suspected wound; if aqueous leaks through, the dye will be diluted and stream downward, producing a dark river through bright green fluorescein. A positive result confirms open globe injury and changes management entirely (no further manipulation, place a rigid eye shield, surgical exploration).

The most accurate test for a suspected intraocular foreign body is a CT scan of the orbit with thin axial and coronal cuts (typically 1 mm). CT identifies radiopaque materials such as metal, glass, and stone with high sensitivity. MRI is contraindicated when metallic material is possible, because the magnetic field can dislodge the fragment and cause catastrophic intraocular injury. B-scan ultrasonography can detect non-radiopaque foreign bodies (wood, plastic) in the posterior segment but should not be performed if the globe is open, due to the risk of pressure-induced extrusion of intraocular contents.

4. Management and Treatment

Step	Intervention	Notes
1. Initial assessment	Visual acuity, rule out open globe	Mandatory before any manipulation
2. Anesthesia	Topical tetracaine 0.5% or proparacaine 0.5%, 1 to 2 drops	For examination only, never prescribed for home use
3. Irrigation	Copious normal saline or balanced salt solution	First-line for loose conjunctival particles
4. Mechanical removal	Moistened cotton applicator (conjunctival), 25 to 27 gauge needle or eye spud (corneal)	Performed under slit lamp with tangential approach
5. Rust ring removal	Ophthalmic burr after 24 hours if needed	Refer to ophthalmology
6. Topical antibiotic	Chloramphenicol 0.5% drops 4 times daily, ofloxacin 0.3% drops, or erythromycin 0.5% ointment 4 times daily for 5 to 7 days	Fluoroquinolone preferred for contact lens wearers (Pseudomonas coverage)
7. Cycloplegic	Cyclopentolate 1% or homatropine 2%, 1 drop 2 to 3 times daily	For pain relief in larger abrasions
8. Tetanus prophylaxis	Tetanus toxoid booster	If organic material or last booster more than 5 years ago
9. Follow-up	Re-examination at 24 hours	Monitor healing and rule out infection
10. Open globe / intraocular foreign body	Rigid eye shield, NPO, intravenous antibiotics (cefazolin plus ceftazidime or vancomycin plus ceftazidime), tetanus, urgent ophthalmology consultation for surgical removal	Do NOT manipulate, irrigate, or measure intraocular pressure

For a superficial conjunctival foreign body, the management is straightforward. After confirming visual acuity and applying topical anesthetic, irrigate the eye with normal saline. If the particle persists, gently sweep it off using a moistened sterile cotton applicator. Prescribe a topical antibiotic such as chloramphenicol 0.5% drops, one drop every 6 hours for 5 to 7 days, and arrange follow-up.

For a superficial corneal foreign body, removal is performed under slit lamp magnification. Approach the cornea tangentially with a 25 to 27 gauge needle on a tuberculin syringe or with a sterile eye spud, lifting the particle off the surface rather than pressing inward. After removal, irrigate the area, then start a broad-spectrum topical antibiotic for 5 to 7 days. Contact lens wearers require fluoroquinolone coverage (ofloxacin 0.3% or moxifloxacin 0.5% drops 4 times daily) because of Pseudomonas risk, and contact lens use must be suspended until full healing.

A rust ring that does not lift cleanly during the initial visit can be left to soften for 24 hours. The patient is then re-examined and the ring is removed with an ophthalmic burr, ideally by an ophthalmologist. Aggressive primary attempts risk creating a deeper stromal defect.

Pain control combines a cycloplegic agent (cyclopentolate 1%, one drop 2 to 3 times daily) to relieve ciliary spasm, plus oral acetaminophen or ibuprofen as needed. Patients must never be given topical anesthetic for home use, because repeated application is toxic to the corneal epithelium and delays healing. Eye patching is not routinely recommended and is contraindicated in contact lens wearers and in injuries involving organic material due to infection risk.

The next best step when an open globe or intraocular foreign body is suspected is to stop the examination, place a rigid eye shield (Fox shield or makeshift shield from a cup), keep the patient NPO, control nausea and pain to prevent Valsalva, administer intravenous broad-spectrum antibiotics (for example cefazolin 1 g every 8 hours plus ceftazidime 1 g every 8 hours, or vancomycin plus ceftazidime in penicillin-allergic patients), update tetanus status, and obtain urgent ophthalmology consultation for surgical exploration and foreign body extraction in the operating theatre. Avoid measuring intraocular pressure, applying ointment, or further palpating the globe.

For organic foreign material (wood, plant matter), clinicians should have a low threshold for ophthalmology referral and consider antifungal prophylaxis because of the risk of fungal keratitis and endophthalmitis.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Looks Similar	Key Discriminator
Simple corneal abrasion	Pain, photophobia, foreign body sensation, fluorescein uptake	No retained particle on slit lamp, history of fingernail or paper trauma rather than projectile injury
Bacterial keratitis (corneal ulcer)	Pain, redness, photophobia, fluorescein uptake	Stromal infiltrate with overlying epithelial defect, hypopyon, more indolent onset over days, often in contact lens wearer
Acute angle closure glaucoma	Severe unilateral eye pain, redness, blurred vision	Mid-dilated fixed pupil, hard globe on palpation, halos around lights, intraocular pressure greater than 30 mmHg, no foreign body history
Open globe injury without retained foreign body	Trauma history, pain, decreased vision	Seidel positive without identifiable particle, peaked pupil, 360-degree subconjunctival hemorrhage, shallow anterior chamber
Viral conjunctivitis	Red eye, tearing, foreign body sensation	Bilateral involvement, watery discharge, preauricular lymphadenopathy, follicular reaction, no fluorescein uptake
Recurrent corneal erosion	Sudden pain on awakening, photophobia, fluorescein uptake	Past history of corneal abrasion weeks to months earlier, no current trauma, no foreign body
Episcleritis	Localized red eye, mild irritation	Sectoral redness that blanches with phenylephrine, no foreign body sensation, no fluorescein uptake
Herpes simplex keratitis	Pain, photophobia, fluorescein uptake	Dendritic ulcer pattern on fluorescein staining, decreased corneal sensation, history of cold sores

6. Traps and High-Yield Pearls

The single most common error on examination questions is failing to document visual acuity before performing any examination or intervention. Whatever else the vignette describes, the first step is always Snellen testing. The second most common pitfall is forgetting to evert the upper eyelid. When a vignette mentions vertical linear corneal abrasions in a patient with foreign body sensation, the test is checking whether you remember that a subtarsal foreign body is the answer, not a simple corneal abrasion.

The classic occupational vignette is the welder, grinder, or worker hammering metal on metal without protective eyewear. This phrasing is engineered to trigger suspicion for an intraocular foreign body, even when visual acuity is preserved and the eye looks deceptively quiet. The correct next step is CT scan of the orbit, not slit lamp manipulation, and never MRI. Choosing MRI in a patient with a suspected metallic intraocular foreign body is one of the most penalized errors on ophthalmology questions.

Remember the Seidel test as the gatekeeper before any foreign body removal attempt. A positive Seidel test transforms the case from a minor procedure into a surgical emergency requiring a rigid shield, intravenous antibiotics, tetanus prophylaxis, and operative management. Manipulating an open globe at the bedside is a guaranteed wrong answer.

Other recurring traps include prescribing topical anesthetic for home use (toxic to the epithelium), patching a contact lens wearer (Pseudomonas risk), missing the rust ring follow-up after a metallic foreign body, and forgetting tetanus prophylaxis with organic material. In contact lens wearers presenting with a red eye and any epithelial defect, fluoroquinolone coverage is mandatory because Pseudomonas keratitis can perforate the cornea within 48 hours.

The core competency being tested is systematic ocular trauma triage: visual acuity first, exclude open globe with Seidel before manipulation, evert the lids, choose the correct imaging (CT, never MRI for metal), and recognize when a quiet-looking eye in a high-velocity occupational setting still demands aggressive workup. Master this sequencing, and foreign body questions become reliable points.

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