Corneal Foreign Body

A corneal foreign body is any material embedded within the cornea that disturbs its normal structure, and sometimes, function. A foreign body may be composed of metal, glass, inert element (eg, silica), plastic, or organic matter. 

Corneal foreign bodies represent a form of ocular trauma. The cornea is exposed to the external environment and thereby susceptible to traumatic injury. Potential foreign bodies may be released during certain activities (grinding metal, high-speed biking, etc), or may be intentionally directed towards the eye or face in an injurious fashion. 

Upon contact with the cornea, depending on the speed, angle of entry, and structure of the foreign body, it may either ricochet off of the cornea, or become embedded within, penetrating initially through the corneal epithelium, and then, through Bowman's layer, the corneal stroma, and Descemet's membrane. If a foreign body strikes the cornea wth sufficient force, it may continue through into the endothelium and into the anterior chamber, creating a penetrating injury, which is beyond the scope of this article. 

Foreign bodies that do not penetrate through the cornea remain embedded within and incite a strong inflammatory reaction. Dilation of ciliary vessels, liberation of white blood cells into the anterior chamber, and edema of the cornea are common. If a foreign body is contaminated with microorganisms, or if it is organic in nature, often, an infectious keratitis also will result. Failure to sufficiently remove a corneal foreign body in a timely manner will also result in infection and continuation of the inflammatory cascade.

Frequency

United States

Foreign bodies are one of the most frequent causes of visits for ophthalmic emergencies. Sometimes, the foreign body may not be present at the time of examination, having left the residual corneal abrasion with resultant pain.

Superficial corneal foreign bodies are much more common than deeply embedded corneal foreign bodies. The possibility of an intraocular foreign body must always be considered when a patient presents with a history of trauma.

In major league baseball, 33% of all eye injuries are corneal abrasions; in the National Basketball Association, corneal abrasions account for 12% of all eye traumas.

International

No difference in frequency is observed internationally.

Mortality/Morbidity

Generally, superficial foreign bodies that are removed soon after the injury leave no permanent sequelae. However, corneal scarring or infection may occur. The longer the time interval between the injury and treatment, the greater the likelihood of complications.

A foreign body is considered an intraocular foreign body if it completely penetrates into the anterior or posterior chambers. When this occurs, ocular morbidity is much more likely. Injury can occur to the iris, lens, and retina, and vision loss may be permanent. Any intraocular foreign body can cause infection and endophthalmitis, a potentially catastrophic condition that can result in loss of the eye.

Sex

Similar to other traumatic injuries, the incidence in males is much higher than in females.

Age

Similar to most other traumatic injuries, the peak incidence is found in the second decade and generally occurs in people younger than 40 years.

Superficial corneal foreign bodies that are not in the visual axis have good prognosis if removed in a timely manner. Incomplete removal, damage to corneal tissue during removal, or, positioning within the visual axis carry a more guarded prognosis as prolonged inflammation and scarring may affect final visual acuity. 

Corneal foreign bodies that penetrate the globe (discussed elsewhere) typically carry a poorer prognosis.

Remind patients of the importance of wearing protective eyewear in any high-risk situation.

Eyes should not be rubbed while working with wood or metal pieces.

If a foreign body enters the eye, the eye should not be rubbed and no attempt should be made by the patient to remove the foreign body.

Patients should attend to their nearest emergency department or urgent care centre for appropriate evaluation at the slit lamp.

For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education articles Eye Injuries and Foreign Body, Eye.

A thorough patient history is essential to ensuring a good patient outcome. It is important to elicit the nature of the traumatic incident as this aids in determining the composition of the foreign body, as well as in triaging the possibility of a penetrating open globe injury, or potential for an intraocular foreign body. Clinicians should ask patients about the activity being done at the time of the trauma, whether any eye protection was worn at the time of the incident, and whether patients rubbed their eyes afterwards or made attempts to remove the foreign body themselves. 

Patients may complain of the following:

• Pain (typically relieved significantly with topical anesthesia)

• Foreign body sensation (typically relieved significantly with topical anesthesia)

• Photophobia

• Tearing

• Red eye

• Decreased vision (especially if the foreign body is in the visual axis)

A complete ophthalmological examination is warranted in all patients with ocular trauma. Once an open globe has been excluded, the patient's visual acuity, pupils, and intraocular pressure should be assessed. Next, a complete slit lamp examination should be performed, with careful attention directed towards the cornea with optical section beams, to allow for assessment of the depth of the corneal foreign body. Assessment of the anterior chamber may show cell and flare, especially with foreign bodies that have been present for more than 24-hours. All patients should undergo a dilated fundus examination to assess for the presence of an intraocular foreign body. If available, B-scan ultrasonography may also be performed to aid in this. 

Patients may present with the following:

• Normal or decreased visual acuity

• Conjunctival injection

• Ciliary injection, especially if an anterior chamber reaction occurs

• Visible foreign body

• Rust ring surrounding the foreign body, especially if a metallic foreign body has been embedded for hours to days

• Epithelial defect that stains with fluorescein

• Corneal edema

• Anterior chamber cell and flare

The patients may be asymptomatic if the foreign body is below the epithelial or conjunctival surface. Over a period of a few days, epithelium often grows over small corneal foreign bodies, with a resultant reduction in pain.

If a corneal infiltrate is present, an infectious cause needs to be considered. Foreign bodies can cause a small sterile inflammatory reaction around the foreign object. However, if a large infiltrate, any corneal ulceration, a significant anterior chamber reaction, or significant pain is present, it should be managed as an infection. See Keratitis, Bacterial.

Corneal foreign bodies can occur as a result of any traumatic incident that releases particulate matter that may strike the eye. These incidents may happen at home (for example, while cleaning), at work (for example, while grinding metal-on-metal), or during recreational activities (for example, while biking at high-speed). 

Causative materials include metal, glass, inert material (silica), and organic matter. 

Complications following a corneal foreign body are typically rare, especially if the foreign body is managed in a timely manner. Nonetheless, complications to consider include:

• Scarring in the visual axis (can lead to permanent loss of vision by disruption of the optical system of the eye)
• Infectious keratitis (more common with organic foreign bodies, or, those that are not removed in a timely manner)
• Corneal decompensation

Unless an infectious corneal infiltrate/ulcer or an intraocular foreign body is suspected, no laboratory work is indicated.

Infectious corneal infiltrates/ulcers generally require scrapings for smears and cultures.

To exclude intraocular or intraorbital foreign body, consider B-scan ultrasound, orbital CT scan (1-mm axial and coronal cuts), and/or ultrasound biomicroscopy (UBM). If the foreign body is metallic, the initial study may include orbital x-ray films. If plain films are negative and a high suspicion still exists for intraocular foreign body, the previously mentioned studies are indicated. These studies should be complemented by a full-dilated examination by an ophthalmologist.

Avoid MRI if a possible history of metallic foreign body exists.

UBM, with high-frequency ultrasound, is often useful to rule out a foreign body embedded in the anterior sclera. These foreign bodies may not be visible because of their nature (eg, glass) or overlying opacity (eg, conjunctival hemorrhage).

Laser in vivo confocal microscopy (IVCO) is particularly sensitive and useful in the diagnosis of hidden corneal foreign bodies.[1]

A Seidel test is performed to rule out corneal perforation in the setting of a deep corneal foreign body.

The lower and upper lids need to be everted to look for additional foreign bodies. If a superficial foreign body is suspected but not found, double eversion of the upper lid to search for a foreign body is required.

Corneal foreign bodies are removed using a sterile foreign body spud or needle after topical anesthesia. Antibiotic is applied to the eye before and after the removal. Cotton-tipped applicators often are not appropriate because of the large surface area of cotton that touches the cornea, potentially creating a large epithelial defect. Because of the risk of corneal scarring and inadvertent globe perforation, this procedure should be completed using a slit lamp biomicroscope and performed by a clinician who is well trained and experienced in corneal foreign body removal.

Rust rings that remain in the cornea after removal of a metallic foreign body may require removal with a rust ring drill. This procedure also should be performed using a slit lamp biomicroscope by a clinician who is well trained and experienced in rust ring removal because of the risk of corneal scarring and inadvertent globe perforation.

Management objectives include relieving pain, avoiding infection, and preventing permanent loss of function.

Topical antibiotic drops (eg, polymyxin B sulfate-trimethoprim [Polytrim], ofloxacin [Ocuflox], tobramycin [Tobrex] qid) or ointment (eg, bacitracin [AK-Tracin], ciprofloxacin [Ciloxan] qid) should be prescribed until the epithelial defect heals to prevent infection.

Topical cycloplegic (cyclopentolate 1% qd/bid) can be considered for pain and photophobia, although a review of the literature shows that they are not effective.[2, 3]

Pressure patch or bandage contact lens is best avoided (unless the epithelial defect is >10 mm2 and then bandage contact lens may be the better option).[2, 4, 5] The following scenarios represent high risk for the patient to develop permanent vision loss. Do not patch if any of the following are present:

• A chance of a perforation of the globe exists.

• A corneal infiltrate is present.

• A chance of a retained intraocular foreign body is possible.

Remove the foreign body using irrigation, a sterile needle, or a foreign body removal instrument. Do not remove if likelihood of penetration through more than 25% of the cornea exists.

Remove a rust ring with an Alger brush or automated burr. Only those clinicians who are trained in and regularly perform this procedure should complete it.

Foreign bodies that present any potential for intraocular penetration must by explored in the operating room. These injuries should be explored within 24 hours of initial examination.

Immediately refer to an ophthalmologist in case of the following:

• Hyphema (blood in the anterior chamber)

• Diffuse corneal damage (focal or diffuse opacity)

• Scleral or corneal laceration

• Lid edema

• Diffuse subconjunctival hemorrhage

• Posttraumatic dilation of pupil or abnormal shape of pupil

• Abnormally shallow or deep anterior chamber compared to the fellow eye

• Persistent corneal defect or corneal opacity

• Any case with possible full penetration of the cornea or sclera

Wear safety goggles in any situation (eg, sports, construction, workshops, industry) that has a high risk of particles or objects flying into the eyes.

Follow up every 2 days until the epithelial defect is well healed and any corneal infiltrates have resolved.

Perform a gonioscopy after the resolution of the problem, and consider annual follow-up care for intraocular pressure if the severity of trauma raises a suspicion for angle-recession glaucoma in later life.

A dilated fundus examination should be performed on a routine basis after any injury severe enough to potentially damage the retina.

An uncomplicated case in which the foreign body is removed can be treated with standard antibiotics. If a large epithelial defect is present, an antibiotic ointment is placed prior to the use of a patch. Complicated cases should be seen by an ophthalmologist immediately and prior to any therapy. For example, if an infiltrate is present, the ophthalmologist may want to scrape and plate the lesion before any antibiotic is instilled in the eye.

Class Summary

Prevent infection of an open corneal abrasion.

Trimethoprim/polymyxin B ophthalmic (Polytrim Ophthalmic Solution)

For ocular infections, involving cornea or conjunctiva, resulting from strains of microorganisms susceptible to this antibiotic. Available as a solution and ointment. Trimethoprim and polymyxin B are rarely sensitizing, and they have a wide spectrum of action in combination.

Gram-positive: S aureus, S epidermidis,Streptococcus species (group A beta-hemolytic and nonhemolytic), S pneumoniae

Gram-negative: P aeruginosa, H influenzae, H aegyptius, E coli, K pneumoniae, P mirabilis (indole-positive), Proteus species (indole-negative), E aerogenes, C freundii, C diversus, A calcoaceticus, M lacunata (some strains), S marcescens

Tobramycin ophthalmic (Tobrex)

Like other aminoglycosides, the bactericidal activity of tobramycin is accomplished by specific inhibition of normal protein synthesis in susceptible bacteria, but very little presently is known about this action. May inhibit bacterial mRNA synthesis, causing inhibition of bacterial growth.

Ofloxacin ophthalmic (Floxin)

Pyridine carboxylic acid derivative with broad-spectrum bactericidal effect.

Ciprofloxacin ophthalmic (Ciloxan)

Inhibits bacterial growth by inhibiting DNA gyrase.

Bacitracin ophthalmic (AK-Tracin, Baciguent)

Prevents transfer of mucopeptides into growing cell wall, inhibiting bacterial growth.

Gatifloxacin ophthalmic (Zymar)

Fourth-generation fluoroquinolone ophthalmic indicated for bacterial conjunctivitis. Elicits a dual mechanism of action by possessing an 8-methoxy group, thereby inhibiting the enzymes DNA gyrase and topoisomerase IV. DNA gyrase is involved in bacterial DNA replication, transcription, and repair. Topoisomerase IV is essential in chromosomal DNA partitioning during bacterial cell division. Indicated for bacterial conjunctivitis due to Corynebacterium propinquum, S aureus, Staphylococcus epidermidis, Streptococcus mitis, S pneumoniae, or H influenzae.

Class Summary

For comfort of the eye and to prevent iris adhesion in cases of traumatic iritis.

Cyclopentolate HCl 0.5-1% (Cyclogyl)

Cyclopentolate is an anticholinergic agent that induces relaxation of the sphincter of the iris and ciliary muscles. When applied topically to the eyes, it causes rapid, intense cycloplegic and mydriatic effects that reach a peak in 15-60 min; recovery usually occurs within 24 h. The cycloplegic and mydriatic effects are slower in onset and longer in duration in patients who have dark pigmented irises.