Corneal Foreign Body Removal

Anatomy and Physiology

The clear cornea is contiguous with the opaque sclera. The corneal tissues are avascular. Nourishment is derived internally from the aqueous humor and externally from the oxygenated tear film.

The cornea is made up of five distinct layers. The epithelium is the outermost layer; its average thickness is estimated at 51 µm.[9] Epithelial cells undergo constant shedding and renewal, and the entire epithelial layer will regenerate and turnover within 2 weeks as new cells migrate from the periphery toward the center.[10] The epithelial healing rate is accelerated after a superficial injury, and most acute epithelial defects will heal within 24 to 48 hours.[11]

Beneath the epithelium is the Bowman membrane. The Bowman cells do not regenerate; therefore, an injury to the Bowman membrane will result in a permanent corneal scar. The stroma, the thickest corneal layer, is inferior to the Bowman membrane, which accounts for nearly 90% of the overall corneal thickness. The stroma primarily comprises collagen fibers (16%) and water (80%). The collagen fibers are precisely configured to allow optimal corneal transparency. Disruption of this stringent orientation causes corneal opacification.

The Descemet membrane is inferior to the stroma. This layer functions as a basement membrane for the corneal endothelium. These basement membrane cells can regenerate if injured. The innermost layer is the endothelium, essential for maintaining the deturgescence of the corneal tissues. Unfortunately, corneal endothelial cells are unable to regenerate. Traumatic damage to the endothelium is problematic as it indicates that the foreign body has penetrated the eye. Additionally, chronic corneal edema can complicate the loss of endothelial cells.

A sixth layer, the Dua layer, has been identified between the stroma and Descemet layer. However, the significance of the Dua layer has not yet been definitively determined.

The iron foreign body is the most common type encountered.[12] An iron foreign body will usually leave rust embedded in the corneal stroma. Rust causes an inflammatory reaction, delays healing, and can promote scarring and corneal irregularity.[13]

Indications

The symptoms suggestive of an ocular foreign body (FB) include pain, foreign body sensation, tearing, photophobia, blepharospasm, and blurred vision. The timely removal of a corneal FB reduces the risks of corneal infection or scarring; these risks increase when embedded foreign matter is left longer.[14] Additionally, removing a corneal FB offers some level of symptomatic relief. Corneal foreign body removal is indicated in the presence of pain, redness, photophobia, blepharospasm, and blurring of vision; when there is a rust ring, corneal infiltrate, or hypopyon; when the FB is deeply embedded in the stroma or Descemet membrane; in the presence of corneal or scleral lacerations, corneal perforation, or an anterior chamber reaction; and when multiple corneal FBs are present.[15]

Contraindications

If an intraocular FB is suspected, an immediate ophthalmologic evaluation is mandatory. Traumatic events resulting in an intraocular FB frequently include metal-to-metal hammering, chiseling, or drilling, or recent proximity to an explosive event.[16] These circumstances suggest a high-speed impact associated with a greater incidence of intraocular FB. Under careful slit-lamp evaluation, signs of intraocular involvement may include a shallow anterior chamber, hyphema, iris or pupillary irregularity, a break in the Descemet membrane, or a traumatic cataract. Additionally, a corneal or scleral perforation will yield a positive Seidel sign, the leakage of intraocular fluid visualized on the ocular surface after introducing fluorescein dye into the tear film.[16][17][16] 

Imaging is beneficial when locating FBs in the posterior segment. Imaging is appropriate if an intraocular foreign body is not visualized but is strongly suspected. Computed tomography (CT) of the orbits can localize foreign bodies. Magnetic resonance imaging (MRI) is strictly contraindicated in any metallic FB case.[18] If a metallic or organic FB is located very deep in the cornea, the risk of penetration or significant scarring warrants an immediate ophthalmologic referral. Removal of foreign bodies causing corneal perforation during slit-lamp examination is not recommended and may cause endophthalmitis. Excessive lid edema is not a direct contraindication to corneal FB removal; the edema should be treated medically and the FB removed at a later date.[14]

Equipment

The following equipment is necessary when removing a corneal FB.

• Topical sodium fluorescein
• Topical anesthetic drops such as proparacaine 0.5% or tetracaine 0.5%
• Slit-lamp with a cobalt-blue filter or a Burton lamp with a similar filter
• Loupe (pediatric patients)
• Sterile saline
• Plastic syringe
• Sterile cotton-tipped applicators
• Jewelers forceps
• 25-, 26-, or 27-gauge needle attached to a tuberculin syringe; a bent needle tip is optional
• Foreign body spud; consider a magnetic spud for metallic foreign bodies
• Rotating burr tool such as an Alger brush
• Eyelid speculum may be necessary
• Topical ophthalmic antibiotics such as ciprofloxacin, moxifloxacin, or gatifloxacin
• Eye patch or pad and bandage

Personnel

A team approach is vital to facilitate the preparation, procedure, and follow-up care required for corneal FB removal procedures. Obtaining a detailed history is indispensable.[14] 

If the patient cannot maintain a stable position at the biomicroscope, it is appropriate to seek nursing assistance to manage the patient's movements throughout the procedure. Team members may include physicians, nurses, ophthalmic technicians, and nursing or ophthalmic assistants.

Each patient should undergo a detailed ophthalmic evaluation by the ophthalmologist. A pharmacist will help in procuring the drugs from the medical store. Ophthalmic assistants help counsel the patient regarding drug use and ongoing follow-up.[19]

Preparation

When a corneal FB is suspected, obtaining a thorough history is essential. Determine the mechanism of the traumatic event and which materials may be embedded in the cornea. Consider the patient's occupation, the location of the accident, and whether eye protection was in use at the time of the trauma.[14] Investigate how the injury ensued. A forceful event with projectile debris increases the suspicion of intraocular involvement or penetration leading to devastating consequences such as endophthalmitis or retinal detachment. Obtain best-corrected entrance visual acuities. If the history is suspicious for a penetrating injury, carefully evaluate the anterior segment for shallowing, pupillary disfigurement, anisocoria, lenticular opacities, hypopyon, or increased cells and flare.[20][21][20] 

Informed consent should be obtained, including the potential risks of infection, corneal scarring or perforation, and vision loss.[22] The slit-lamp biomicroscope enables a detailed evaluation of the superficial ocular structures. However, when a slit-lamp is unavailable, various light and magnification systems can identify most FB.

The location and depth of any FBs should be determined.[23] Eyelid eversion is necessary to establish whether any additional debris is hidden beneath the eyelids. The lower tarsal conjunctiva should be examined by pulling down the lower lid and looking for any residual debris or foreign body. Similarly, the upper tarsal conjunctiva should be examined by the single or double version of the upper lid. The upper lid can be everted by gently using the thumb or by using a cotton tip applicator.[24] Carefully evaluate the ocular surface of both eyes, with and without sodium fluorescein. Using a cobalt-blue filter, confirm that the fluorescein staining pattern is stable and the Seidel sign is absent. If the Seidel sign is present, discontinue preparation. Intraocular penetration has occurred, and the patient must be sent for immediate ophthalmologic evaluation.[25][24][25]

The corneal surface must be adequately anesthetized before any potential contact with the cornea. Place one or two drops of topical anesthetic into the lower fornix and wait at least 30 seconds for the full anesthetic effect. The patient must be stabilized at the biomicroscope with the forehead firmly applied to the forehead strap and the chin on the chin rest.[26] This position is crucial to prevent any trauma to the patient; they must remain still throughout the procedure. Care team members should assist in stabilizing patients who are at risk for disruptive reflex head movements. Identify a visual fixation target to facilitate a safe and direct approach to the FB and reduce the potential for eye movements during the procedure.

A strong blinking reflex may require the use of an eyelid speculum.[27]

Technique or Treatment

It is imperative to use the least invasive technique that will allow the effective removal of the corneal FB, using more invasive measures only as necessary.[14] Occasionally, a superficial FB can be displaced with a sterile saline lavage or elevated from the corneal surface with a moistened sterile cotton-tipped applicator. If the FB is firmly embedded, a needle or a spud will be required to dislodge it. Stabilize the approaching hand across a bony facial structure to yoke the two.[28] Approach the corneal surface tangentially from the periphery, with the bevel of the needle facing outwards. Very gently lift the foreign body away from the cornea until wholly dislodged. Magnetized FB spuds facilitate the removal of metallic FBs. An iron FB forms a rust ring in as few as 4 hours.

A dense rust ring can be removed by brushing a sterile rotating burr across the affected tissues. An Alger brush device can effectively debride the corneal rust ring, enhancing visual outcomes. Ideally, the internal clutch mechanism will, with excessive pressure on the Bowman membrane, disengage the burr and prevent deeper penetration. However, if the Bowman membrane has been compromised, there is not sufficient resistance to halt the device, and additional scarring will occur if too much tissue is compromised.[14] The burr requires gentle pressure tangential to the affected corneal surface. Increasing the depth and area of treatment will prolong corneal healing time. Do not risk pursuing capacious treatment leaving a central corneal scar or extensive thinning; any remaining faint deposits will migrate anteriorly and slough off quickly.[29]

If a deeply embedded FB is determined to be physiologically inert, like glass or plastic, it can be left in place and observed. While removing the foreign body, care should be taken to avoid pushing the foreign body with a bud or needle to avoid deeper entry into the cornea.[14]

Medical Management Following Corneal Foreign Body Removal

Antibiotics after corneal FB removal decreases the risk of superinfection.[30] Initiate a broad-spectrum topical antibiotic no less than 4 times daily for 1 week. More extensive, deeper, or central defects may require more frequent applications and longer durations. If the patient is a habitual contact lens wearer, ensure the antibiotic therapy is effective against Pseudomonas. Commonly used topical ophthalmic antibiotics are ciprofloxacin, ofloxacin, moxifloxacin, and gatifloxacin due to their broad spectrum coverage. Ophthalmic ointment formulations have a better retention time, so they should be used at night. Ophthalmic solutions like sulfacetamide are easy to apply and improve patient compliance.[31] Oral antibiotics have a limited role and are used only when there is an associated scleral infection or endophthalmitis.[32]

Topical ophthalmic antifungals such as natamycin, itraconazole, and voriconazole are advised when there is a history of vegetative matter injury and associated corneal infiltrate. The decision to start antifungals is based on clinical judgment and patient history to safeguard the patient from keratitis.[33] Oral antifungals such as ketoconazole and fluconazole are rarely needed and are indicated only for nonresolving fungal infiltration with hypopyon and scleritis.[34]

Topical lubricants such as carboxymethylcellulose and hydroxypropyl methylcellulose play an important role in managing corneal foreign body cases, helping to heal the epithelial defect, wash away the debris, maintain the ocular surface, and reduce ocular irritation.[35] Corticosteroids in any form are contraindicated and should be avoided due to the risks of worsening underlying infection and superimposed infection.[36]

Analgesia Following Corneal Foreign Body Removal

Pain will lessen as the epithelium heals and the associated inflammation resolves. The use of topical anesthetic to provide analgesia after the procedure is not recommended, although some practitioners will prescribe topical anesthetics for pain relief for the first 24 to 48 hours, as it has proven beneficial in the initial period without any side effects.[37] If there is no epithelial defect but a patient is particularly symptomatic, topical ophthalmic nonsteroidal anti-inflammatory medications can be beneficial. If breakthrough pain requires additional analgesia, consider over-the-counter oral analgesics. Unless contradicted, alternating acetaminophen and ibuprofen offer sufficient pain relief until the corneal surface structures normalize. A schedule III controlled substance is rarely needed.

Topical ophthalmic corticosteroids are generally avoided until the epithelium has completely healed.[38] The Steroids for Corneal Ulcers Trial (SCUT) investigated the potential risks and benefits of corticosteroids in active corneal ulceration and found a role for steroids in conjunction with antibiotic therapy.[39] While this study specifically evaluated the treatment of infectious keratitis, the results have been extrapolated to other corneal conditions. In the case of a deep foreign body with significant surrounding inflammation, a pulse of topical ophthalmic corticosteroids may reduce the risk of ensuing scarring. However, if there is a relatively shallow injury with a limited inflammatory reaction, it is advisable to confirm that the epithelium has healed and subsequent infection has been ruled out before initiating topical steroids. 

The anti-inflammatory actions of amniotic membrane therapy may be beneficial in reducing residual scarring while encouraging epithelial healing.[40] A short-acting topical cycloplegic agent can reduce any associated discomfort if an anterior chamber reaction is observed. If the patient is particularly symptomatic, a short course of cyclopentolate or homatropine twice daily for cycloplegia should be prescribed; this can be used with topical steroid therapy once epithelial closure is complete.  

A bandage soft contact lens may be considered to relieve pain, correct vision, and reduce surface disruption associated with blinking; caution should be exercised if infection is a concern. Pressure patching is typically not performed unless there is an extensive concomitant corneal abrasion.[41] 

Patching of the affected eye is usually avoided in abrasions secondary to corneal FB injury. There is early healing, less blurred vision, and even less pain without an eye patch. A large epithelial defect affecting more than 50% of the corneal surface can be patched but can also be managed without patching under close supervision.[42]

The standard of care dictates that the patient be seen within 24 hours following corneal FB removal.[43]

Complications

There should be a concern for potential complications if the patient does not report that their status is stable or improving. Evaluation of the ocular surface should be repeated 24 hours after corneal FB removal assessing for additional foreign bodies, nonhealing defects, or ulceration. Seidel testing should be repeated, and the anterior chamber should be reevaluated for shallowing, pupillary disfigurement, lenticular opacities, hyphema, hypopyon, or increased cells and flare.[44] 

Various complications of corneal FB injury include the following:

• Persistent conjunctivitis
• Nonhealing epithelial defect
• Corneal infiltrates, scarring, thinning, or perforation
• Rust ring formation
• Secondary glaucoma
• Anterior uveitis
• Iridodialysis
• Traumatic mydriasis
• Angle recession with subsequent glaucoma
• Anterior and posterior synechiae
• Anterior and posterior capsular tear or rupture
• Traumatic cataract
• Zonular dialysis
• Vitreous prolapse
• Retinal tears or incarceration of foreign bodies
• Retinal or choroidal detachment

Clinical Significance

While a corneal FB may present insidiously, it will more frequently present with the acute onset of multiple nonspecific ocular symptoms, including hyperemia, eye pain, decreased visual acuity, blepharospasm, and photophobia. The timely removal of a corneal FB significantly reduces the potential for corneal compromise.

The nature of the inciting event may determine the course of healing. While small, superficial FB are easily removed with little risk of adverse sequelae, those more deeply embedded or centrally located are likely to result in visually significant scarring.[45] The environmental debris may be contaminated by inoculating bacterial, viral, or fungal elements leading to subsequent infection.

Penetrating ocular injuries may have dire effects leading to blindness. A positive Seidel sign indicates a corneal perforation. Iris and pupillary abnormalities, hyphema, and lenticular trauma suggest serious ocular trauma. Suspect intraocular penetration if, despite meticulous examination, no FB is found. It is imperative to seek emergency ophthalmic care if intraocular trauma is suspected.[16]

Enhancing Healthcare Team Outcomes

When counseling patients, the healthcare team should reinforce the need for protective eyewear to diminish the risk of ocular trauma. Evidence of prior corneal scarring suggests previous injuries due to similar past events. Occupational settings, hobbies, and environmental factors may contribute to eye injuries. Any monocularly functioning patients should be prescribed full-time protective eyewear and strongly encouraged to use it to protect their only seeing eye.[46] 

Patient outcomes are improved when the team can rule out the signs of FB intraocular penetration. The team must ensure that a careful slit lamp exam and a dilated fundus exam are done promptly.[47]

The nursing team, allied health staff, and interprofessional support framework play a key role in recruiting the emergency corneal foreign patients to the clinic, making the patient comfortable, assisting the patient with the slit lamp and operating room for foreign body removal, explaining the medications and counseling regarding natural course of the pathology, associated complications and the need for follow up.[48][49]