Benda Asing Mata

01Pathophysiology

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).

02Classification of Clinical Manifestation

03Diagnostic Workup

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.

04Management and Treatment

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.

05Differential Diagnosis and Distractors

06Traps 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.