CORNEAL FOREIGN BODY

Signs and Symptoms

Typically, corneal foreign body injuries present as an emergency following acute injury, making them a common urgent clinical entity of ophthalmic practice.1-12 Patients present with acute pain, photophobia, pain upon extraocular muscle movement and blinking, lacrimation, blepharospasm, foreign body sensation, variably blurry vision (depending upon the location of the particle) and a history of having something “go in their eye.”1-9 In rare cases, the patient may be asymptomatic.

Biomicroscopic examination often reveals diffuse corneal edema and epithelial disruption. In severe cases, when edema is excessive, folds in Descemet’s membrane may be present. Circumlimbal injection with a greater density of conjunctival erythema adjacent to the site of injury is common if the injury induces anterior uveitis. Cobalt blue light inspection, with the instillation of sodium fluorescein dye, will illuminate the damaged cornea.8

There is no gender predilection specifically; however, the majority of affected individuals are young, typically under age 20 and male.12-15 Workshop equipment, tools, the activity of construction and motorized lawn equipment are all notable sources of ocular injury.12,14,16,17 Inorganic foreign bodies (plastic, glass) tend to be better tolerated than organic material (wood).9

Pathophysiology

The cornea has five distinct layers: the corneal epithelium, Bowman’s membrane (a whirling structure designed to prevent penetrating injuries), the organized 250 lamellar sheet stroma, Descemet’s membrane and the metabolic endothelium.19-24 There are two categories in which corneal foreign bodies may injure the cornea: superficial (not involving Bowman’s membrane) and deep (penetrating Bowman’s but not rupturing Descemet’s membrane). Corneal foreign bodies typically enter the epithelium but are prevented from penetrating deep into the tissue by Bowman’s membrane.23 Foreign objects piercing Bowman’s membrane will typically leave a permanent scar.15,16

The cornea has remarkable healing properties. The epithelium adjacent to any insult expands in size to fill in the defect, usually within 24-48 hours.18 Below the epithelium, there is no mechanism for cellular replacement. Here, cells enlarge (polymegathism), change shape (pleomorphism) or move over.24

Lesions that are purely epithelial often heal quickly and completely without scarring. Unfortunately, if there is any collateral destruction of limbal stem cells, superficial corneal injuries may develop into recurrent epithelial ulcerations, chronic stromal ulcers with deep stromal vascularization, or develop conjunctival overlap.25-27 Corneal avascularity is moderated by anti-angiogenic factors.26,27 These factors counterbalance pro-angiogenic/lymphangiogenic factors that are constantly available, becoming upregulated during wound healing.27 Angiogenic proteins (vascular endothelial growth factor and basic fibroblast growth factor) and angiogenesis regulatory proteins, along with matrix metalloproteinases and lymphangiogenic regulatory proteins, all play vital roles during corneal wound healing.27

All corneal injuries induce an inflammatory reaction that exerts trophic influences in the corneal epithelium, damaging sensory nerves.28 Alterations in normal healing disrupts the integrity and function of the tissue with undesirable consequences, ranging from inability to wet with resultant loss of transparency to infectious ulceration and perforation.28

Management

Treatment of an injury due to corneal foreign body begins with a problem-oriented history. Since patients are often in distress, the process should be streamlined and succinct. The time, place and activity surrounding the injury should be recorded. Visual acuity (VA) should be recorded, if possible, before any procedures or drops are given. If the blepharospasm and photophobia are sufficiently intense, one drop of topical anesthetic can be administered to allow for VA measurement.

The examination should include pupil testing and an external evaluation of the adnexa and then proceed to biomicroscopy. The eyelids should be everted and fornicies scrutinized to rule out the presence of hidden foreign material. Fluorescein dye (preferably without anesthetic) should be instilled to assist in identifying corneal defects and locating potential debris. The Seidel test (painting of the wound with fluorescein dye and observing for aqueous leakage) should be performed if a full-thickness cornea/globe perforation is suspected or the foreign material hit the eye at high speed.

Any injury should be documented for size, shape, location and depth. Corneal abrasions should be cleaned and scrutinized for foreign matter. The anterior chamber should be evaluated for uveitis. A dilated examination should be completed (either at time of initial evaluation or soon at follow-up) to rule out any posterior effects from the trauma and rule out penetrating foreign body.

Corneal foreign bodies can be removed using stream lavage with sterile saline, forceps, a cotton-tipped applicator, or a foreign body spud or a loop. However, among the most popular instruments is a hypodermic needle mounted on a syringe.29-33 This method affords several advantages: sterility, reach, control over the size of the probe (23- to 30-gauge typically), sharpness for mild excavation, availability, inexpensive cost and ease of use.

Generally, the procedure is accomplished following the administration of one or two drops of a topical anesthetic such as proparacaine.32,33 If the patient is unable to maintain eyelid opening, a lid speculum may be required. The patient should maintain a gaze that affords the clinician the best lateral approach to the entrapped particle. If the corneal foreign body is a “corneal splinter,” the best approach may be with a forceps; however, the technique for reaching the foreign body is still safe and sound.

In the event the foreign body is metallic and has oxidized, the resultant ‘rust ring’ should be removed at the time of the foreign body, as long as it is determined to be safe from enlarging the potential scar zone. Some clinicians prefer the use of a motorized burr (Alger brush) to lift superficial rust rings; however, often these devices inadvertently enlarge the region of corneal abrasion around the residual crater and, in some cases, can penetrate a weakened cornea. If the risk-to-benefit ratio for rust removal is significant, the rust can be left to advance to the surface during the healing process where it can be more easily removed later.34 Rust-ring infiltrate does not serve as an indicator of corneal infection.35

The treatment for the residual superficial corneal injury is universal. Pain can be mitigated using cycloplegia (atropine 1% QD-TID, for the worst and homatropine 5%, in the office, for the mildest), and topical non-steroidal anti-inflammatory medications BID-QID. Infection can be prevented using topical antibiotics.36-40 Bed rest, inactivity, cold compresses, artificial tear drops and over-the-counter analgesics (acetaminophen or ibuprofen) can be used to relieve acute pain. In cases where pain is severe or the abrasion extensive, a thin, low-water-content bandage contact lens can be applied.38-43 Pressure patching is not contraindicated, although it is no longer considered standard-of-care.38-43

Patients should be reevaluated every 24-48 hours until the injury demonstrates a restored epithelium.37-39 Topical lubricants and antibiotic ointment at bedtime can provide analgesia and cushioning to the lesion during the reparative process. Topical steroids can be added after the initial healing has taken place to prevent subepithelial infiltration and to mitigate inflammation. An alternative approach involves a fixed topical antibiotic/steroidal combination preparation where appropriate.

Clinical Pearls

A peaked pupil, full-thickness corneal defect, focal lenticular opacity or disproportionate inflammation (hypopyon) may be indicative of a penetrating injury.

High-speed particles that are hot have the potential to enter the cornea and produce self-sealing wounds. Here, particles may enter the interior areas of the eye without producing a Seidel sign.

In cases where necrotic, loose epithelium impairs healing, a cotton-tipped applicator saturated with anesthetic may be used to debride the loose or excessive tissue.

When significant uveitis is present or if subepitheial infiltration occurs during the reparative process, topical steroids may be required.

Rapid, aggressive subepithelial infiltration, increased pain and increased injection in the setting of an epithelial break may be a sign of infection. Lesions such as these should be considered vision threatening, warranting immediate treatment with a fourth-generation fluoroquinolone antibiotic (if one is not already employed).

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