Corneal foreign bodies are a commonly encountered presentation in the ambulatory urgent care and emergency room setting, second only to corneal abrasions in their frequency. Often, corneal foreign bodies are the result of inadequate eye protection coupled with a risky activity, such as grinding metal-on-metal. Most corneal foreign bodies do not cause significant mortality or morbidity, however, those in the visual axis, and those that strike the eye at high speed, carry the potential for sight-threatening complications. Timely recognition and appropriate removal of a foreign body is key to ensuring an optimal patient outcome.
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 such items as metal, glass, inert element (eg, silica), plastic, or organic matter, to name a few.
Corneal foreign bodies represent a form of ocular trauma. The cornea is directly 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 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 with 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 adequately remove a corneal foreign body in a timely manner can result in infection and continuation of the inflammatory cascade.
Corneal foreign bodies are an exceptionally common cause for emergency health care visits. Although true frequencies are difficult to estimate, given the varied etiologies that can result in a foreign body within the cornea, estimates within the literature place the incidence at 40% of ocular injuries as a whole (which occur at 8.1 per 1000).
Generally, superficial foreign bodies that are removed soon after the injury leave no permanent sequelae, though in some cases, corneal scarring or infection may occur, which are discussed in detail later in this article. 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. Discussion of penetrating injuries and intraocular foreign bodies is beyond the scope of this article.
Similar to other traumatic injuries, the incidence in males is much higher than in females.
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 ocular 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. Patients who are monocular should wear a pair of glasses with polycarbonate lenses, regardless of whether they require refractive correction, at all times.
Eyes should not be rubbed while working with wood or metal particles.
If a foreign body enters the eye, the eye should not be touched 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 circumstances of the injury (for instance a high-velocity projectile from grinding metal-on-metal or cutting wood, or a low-velocity projectile from working under a car and particles falling via gravity), 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 ophthalmologic 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
· Corneal infiltrate
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 must 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 (with or without hypopyon), 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, cleaning), at work (for example, grinding metal-on-metal), or during recreational activities (for example, biking at high-speed).
Causative materials include metal, glass, inert material (silica), and organic matter (wood), among others.
Complications following a corneal foreign body typically are 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
When evaluating any patient with ocular trauma, obtaining a good history with a clear mechanism is crucial (low- versus high-velocity impact).
All cases of foreign body injury to the eye should be carefully approached and a penetrating injury with an open globe should be excluded.
Routine assessment of corneal foreign bodies does not warrant any laboratory studies.
Corneal infiltrates that are present with foreign bodies, or those that appear following their removal, should be swabbed/scraped for Gram stain, culture, and specificity studies to guide antimicrobial therapy.
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 fundus examination by an ophthalmologist.
Avoid MRI if a possible history of metallic foreign body exists because this may result in dramatic migration of the metallic foreign body through ocular tissues, leading to increased morbidity.
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, though is not often available in routine practice.[1]
A Seidel test at the slit lamp biomicroscope 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 or if no foreign body is visible initially at the slit lamp. If a superficial foreign body is suspected but not found, double eversion of the upper lid to search for a foreign body is advised.
Corneal foreign bodies may be removed at the slit lamp biomicroscope. The patient should be counseled on remaining very still with their chin and forehead flush to the slit lamp and directing their gaze to a predetermined fixation point. Ample topical anesthetic should be instilled. If patient cooperation is a concern, a lid speculum should be placed to hold the eye open. A 25-gauge needle or a fine battery-powered burr may be used to gently lift the corneal body from the underlying tissue. Care should be taken to avoid iatrogenic injury to surrounding cornea. Once the foreign body has been removed, our practice is to place one drop of povidone-iodine to sterilize the eye, and one drop of topical antibiotic.
Clinicians should be careful not to be too aggressive in pursuing the removal of a foreign body or ‘rust ring’. Often, ‘rust rings’ that are initially difficult to remove, soften with time and work their way forwards, facilitating removal. Moreover, in removing ‘rust rings’, clinicians should be careful to debride only particulate matter, not rust-coloring within the cornea. Coloring indicates molecular iron, which does not impact vision, and may reduce over time. Extensive debridement of the cornea in pursuit of the removal of rust coloring may lead to a larger scar once healing is complete.
Caustic foreign bodies (such as calcium hydroxide or cement elements) may require chemical burn protocols along with removal.
Management objectives include relieving pain, avoiding infection, and preventing permanent loss of visual function.
Once a corneal foreign body has been successfully removed, medical therapy should be initiated.
Topical antibiotic drops (eg, polymyxin B sulfate-trimethoprim [Polytrim], tobramycin [Tobrex] qid) or ointment (eg, bacitracin [AK-Tracin], ciprofloxacin [Ciloxan] qid) should be prescribed until the epithelial defect heals to prevent infection. If available, third or fourth generation fluoroquinolines, such as moxifloxacin [Vigamox], gatifloxacin [Zymar], ciprofloxacin [Ciloxan], or ofloxacin [Ocuflox] should be considered as first-line therapy. In settings where antibiotic availability is limited, chloramphenicol is also a viable option.
A 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]
Topical steroids should be avoided in the acute phase, especially if the foreign body was of organic material.
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]
Clinicians should be careful to never place a pressure patch on an eye that has a laceration as this may worsen a potential open globe injury by inciting herniation of intraocular contents. In eyes where there is a concern for a penetrating wound or open globe, a clear plastic shield should be placed over the eye instead.
Corneal foreign bodies should be removed at the slit lamp as described previously and never with the naked eye. No specific surgical or operative intervention is indicated.
If a penetrating wound is present, a globe exploration and globe rupture repair must be undertaken, in the operating room.
Intraocular foreign bodies must be removed in the operating room by surgeons trained in posterior segment surgery.
Immediately refer to an ophthalmologist in case of the following:
Corneal foreign bodies may result in scarring at the site of initial injury, compromising vision through three mechanisms (either individually, or together): loss of transparency, irregular astigmatism, and glare.
Foreign bodies composed of organic matter, or those that have been present for an extended period of time, may result in concomitant infectious keratitis (discussed elsewhere), with its associated potential for complications. Organic foreign bodies often are associated with fungal keratitis, which can be more difficult to diagnose and manage, and should be treated by an ophthalmologist.
Safety goggles, with wraparound functionality, ideally creating a seal around the periorbital skin, should be worn during any high-risk activity (for example, grinding metal-on-metal, woodworking, biking at high speeds, etc). Monocular patients should consider wearing eye protection at all items.
Once a corneal foreign body has been successfully removed, patients should be followed frequently, daily if possible, until their underlying epithelial defect has closed.
Patients should be monitored for the appearance of a corneal infiltrate, signaling potential infection, and the need for more aggressive antimicrobial therapy. Concomitant increased intraocular inflammation (cell, flare, hypopyon) often also is present with infectious infiltrates.
Patients who have scarring from their corneal foreign body may have vision loss due to decrease in corneal transparency, increase in irregular astigmatism, or glare, some or all of which can be difficult to treat. Irregular astigmatism sometimes may be managed with specialty contact lenses. Superficial scars can be treated with excimer laser surgery in the form of phototherapeutic keratectomy (PTK) or photorefractive keratectomy (PRK), whereas deeper scars or significant irregularities may require lamellar or full-thickness corneal graft procedures. Detailed discussion of these interventions is beyond the scope of this article.
Often, with sufficient time, even patients with central or paracentral scars in the visual axis may notice a marked improvement in their vision, making watchful waiting a potential alternative.
Clinical Context: 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
Clinical Context: 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.
Clinical Context: Pyridine carboxylic acid derivative with broad-spectrum bactericidal effect.
Clinical Context: Inhibits bacterial growth by inhibiting DNA gyrase.
Clinical Context: Prevents transfer of mucopeptides into growing cell wall, inhibiting bacterial growth.
Clinical Context: 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.
Clinical Context: 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.
For comfort of the eye and to prevent iris adhesion in cases of traumatic iritis.