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Cornea Foreign Body Removal


Cornea Foreign Body Removal

Article Author:
Christian Guier
Article Editor:
Thomas Stokkermans
Updated:
5/21/2020 8:50:26 AM
For CME on this topic:
Cornea Foreign Body Removal CME
PubMed Link:
Cornea Foreign Body Removal

Introduction

Patients with corneal abrasions and foreign bodies (FB) commonly present to emergency departments, urgent care centers, primary care, and eye care providers.[1][2][3] The cornea is the most richly innervated tissue in the body.[4] Patients with corneal FB may report multiple ocular symptoms, including pain, photophobia, decreased vision, copious tearing, blepharospasm, and conjunctival hyperemia. Typically the event has an acute, easily identified onset. Infrequently, the FB is acquired obscurely and suspected only after mild ocular symptoms persist. Patients frequently report that the FB was lodged in the eye while outside or coincidentally while working in the yard or on a home improvement project. Perhaps more worrisome are injuries that involve the high-velocity mechanics associated with hammering, grinding, and drilling metals.

The cornea is crucial for focusing light on the retina, allowing functional vision. As much as 67% of the focusing power of the eye is derived at the cornea. A corneal injury will cause physical and functional discomfort. Subsequent corneal edema leads to photophobia and decreased visual acuity. When objects are deeply embedded, corneal scarring or irregularities may occur, resulting in significant visual disruption. 

The cornea is essential for physically protecting the internal structures of the eye from external elements.[5] The dense, boney orbital structures encompassing the eye also help to protect the ocular surface. To a greater extent, the blinking of eyelids and lashes, as well as the formation of reflex tears, attenuates the accumulation of foreign matter on the cornea. Of utmost concern is the potential for intraocular penetration, which may lead to devastating consequences, including endophthalmitis or retinal detachment. 

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. Thickness is estimated to be 51 microns in normal eyes.[6] Epithelial cells undergo constant shedding and renewal. The entire epithelial layer will regenerate and turnover within 2 weeks as new cells migrate from the periphery toward the center.[7] The rate of epithelial healing is accelerated after a superficial injury has occurred.[8] Most acute epithelial defects will convalesce within 24 to 48 hours. Beneath the epithelium lays 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 is, by far, the thickest layer making up nearly 90% of the overall corneal thickness. It is composed primarily of collagen fibers (16%) and water (80%). The collagen fibers are precisely configured to allow optimal corneal transparency. Disruption of this stringent orientation causes opacification. The Descemet membrane is posterior to the stroma. This layer functions as a basement membrane of the corneal endothelium. These cells can regenerate if injured. The innermost layer is the endothelium. These cells are essential for maintaining the deturgescence of the corneal tissues. Corneal endothelial cells are unable to regenerate. Traumatic damage to the endothelium is worrisome as it indicates that the foreign body penetrated the eye. Additionally, with the loss of endothelial cells, chronic corneal edema is a possible complication. A sixth layer, Dua layer, has been identified between the stroma and Descemet layer. Its significance has not been definitively determined at this time. The iron foreign body is the most common type encountered.[9] 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.[10]

Indications

The symptoms suggesting that an ocular foreign body (FB) is present include pain, foreign body sensation, tearing, photophobia, blepharospasm, and blurred vision. The timely removal of a corneal FB is appropriate. Removing a FB offers some level of symptomatic relief. Risks for corneal infection or scarring increase when embedded foreign matter is left for a longer duration.

Contraindications

If an intraocular foreign body (FB) is suspected, then an immediate ophthalmologic evaluation is mandatory. History of intraocular foreign body trauma frequently includes metal to metal hammering, chiseling or drilling, or recent proximity to an explosive event. These circumstances suggest a high-speed impact, which is associated with a greater incidence of intraocular FB. With 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 positive Seidel sign (leakage of intraocular fluid visualized on the ocular surface after fluorescein dye has been introduced into the tear film) indicates a corneal or scleral perforation. Imaging is of benefit when locating foreign bodies in the posterior segment. Magnetic resonance imaging (MRI) is strictly contraindicated in any case involving metallic FB. Regardless of superficial corneal foreign bodies, if an intraocular foreign body (FB) is suspected, then an immediate ophthalmologic evaluation is mandatory.

If a metallic or organic FB is located very deep in the cornea, the risk of penetrating or significant scarring warrants a specialist referral.

Equipment

  • Topical sodium fluorescein
  • Topical anesthetic drops (proparacaine 0.5% or tetracaine 0.5%)
  • Slit-lamp with a cobalt blue filter or a Burton lamp with a similar filter
  • Sterile saline
  • Sterile cotton-tipped applicators
  • Jewelers forceps
  • 25 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 (Alger brush)
  • Eyelid speculum may be necessary

Personnel

A care team approach is vital to facilitate the preparation, the procedure, and follow-up care required for corneal foreign body (FB) procedures. Obtaining a detailed history is indispensable. If the patient is unable to 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.

Preparation

When a corneal foreign body (FB) is suspected, obtaining a thorough history is essential. Determine the mechanism of the traumatic event, including 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. Investigate how the injury ensued. A forceful event with projectile debris increases the suspicion for intraocular involvement. Obtain best-corrected entrance visual acuities. Perform a careful pupillary examination with attention to whether any anisocoria is present or if there is an abnormally shaped pupil. 

Before performing the procedure review, the possible risks including the potential for infection, corneal scarring, corneal perforation, or vision loss. A signed informed consent form should be obtained and included in the documentation.

The use of the slit-lamp biomicroscope enables a detailed evaluation of the superficial ocular structures. However, when a slit-lamp is not available, a variety of light and magnification systems can serve to identify most FB. Initially, the location and depth of any foreign bodies should be determined. Eyelid eversion is necessary to establish whether any additional debris is hidden beneath the eyelids. Carefully evaluate the ocular surface of both eyes, with and without sodium fluorescein. Confirm that the fluorescein staining pattern is stable without observing any dark downward streaming disruption (Seidel sign). If the Seidel sign is positive, discontinue preparation. Intraocular penetration has occurred, and the patient must be sent for immediate ophthalmologic evaluation.

The patient must be properly anesthetized by placing one or two drops of topical anesthetic into the lower fornix at least 30 seconds prior to any potential contact with the cornea. It is necessary to communicate to the patient how the procedure should proceed and what is expected of them. The patient must be stabilized at the biomicroscope. Care team members should assist in immobilizing patients who are at risk for disruptive reflex head movements. A fixation target should be identified to facilitate a safe and direct approach to the foreign body while reducing the potential for eye movements during the procedure. Infrequently an eyelid speculum will be necessary to account for a strong blinking reflex. When approaching the corneal surface with a needle or a spud, stabilizing the operative hand on a boney facial structure is helpful.

Technique

It is necessary to pursue the least invasive technique that will allow effective removal of the corneal foreign body (FB). Use more invasive measures only as necessary. Occasionally, the FB is superficial, and it can be displaced with a sterile saline lavage. A moistened sterile cotton-tipped applicator may be used to elevate a superficial FB away from the surface. If the FB is firmly embedded, a needle or a spud will be required to dislodge it. Stabilize the approach by placing the practitioner's hand across a boney facial structure to yoke the two. Approach tangentially from the periphery with the bevel facing outwards. Very gently lift the foreign body away from the cornea until completely dislodged. Magnetized FB spuds facilitate the removal of metallic FB. 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 ultimate visual outcomes. The burr requires gentle pressure tangential to the affected corneal surface. Keep in mind that increasing the depth and area of treatment will influence the time required to heal. Do not risk pursuing capacious treatment leaving a central corneal scar or extensive thinning. Any remaining faint deposits will migrate anteriorly and slough off in a short time. If a deeply embedded FB is determined to be physiologically inert, like glass or plastic, it can be let in place and observed over time.

Post Treatment:

Initiate a broad-spectrum topical antibiotic for no less than 4 times daily for one week. Larger, deeper, or central defects may require more frequent applications and longer durations. If the patient is a habitual contact lenses wearer ensure that the antibiotic therapy is effective against pseudomonas. 

Expect pain symptoms to improve as the epithelium heals and the associated inflammation resolves. Utilize topical anesthetics only in-office to manage the patients' symptoms throughout the procedure. Home therapy using topical anesthetics is not recommended. When a patient is particularly symptomatic, topical non-steroidal anti-inflammatory medications can be beneficial. If breakthrough pain requires additional consideration, 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 may be necessary for rare instances.

Topical steroids are generally avoided until the epithelium has completely healed.[11] The Steroids for Corneal Ulcers Trial (SCUT) did investigate the potential risks and benefits of steroids in active corneal ulceration. They found a role for steroids in conjunction with antibiotic therapy.[12] This study specifically evaluated the treatment of infectious keratitis, but 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 steroids 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.[13]

If an anterior chamber reaction is observed, a short-acting topical cycloplegic agent can be used to reduce the associated discomfort. A short course of cyclopentolate or homatropine twice daily for cycloplegia should be prescribed if the patient is particularly symptomatic. This can be used in conjunction with topical steroid therapy once epithelial closure is realized.  

A bandage soft contact lens may be considered to relieve pain, correct vision, and reduce surface disruption associated with blinking. However, this should be done with caution if there is a concern for infectious agents. Amniotic membrane therapy has been found to catalyze epithelial healing while reducing inflammation and the potential for corneal scarring. Pressure patching is typically not performed unless there is a large concomitant corneal abrasion. 

The standard of care dictates that the patient is to be seen again in 24 hours to evaluate status.

Complications

Of utmost concern is the potential for intraocular penetration, which may lead to devastating consequences, including endophthalmitis or retinal detachment. If the history is suspicious for a penetrating injury, carefully evaluate the anterior segment for shallowing, pupillary disfigurement, lenticular opacities, hypopyon, or increased cells and flare. Sodium fluorescein applied to the ocular surface definitively identifies the site of the ocular injury. Carefully perform a Seidel test by applying sodium fluorescein superior to the suspected wound. If a dark stream is seen flowing inferiorly, it is leakage of aqueous humor confirming that a full-thickness corneal injury has occurred. Even in the event of a negative Seidel test, intraocular debris may be present. Very small corneal foreign bodies may conceivably create subtle self-sealing lacerations. A dilated fundus examination is mandatory to seek the presence of any penetrating foreign bodies. If an intraocular foreign body is not visualized by strongly suspected, then imaging is appropriate. Computed tomography (CT) of the orbits can localize foreign bodies. Magnetic resonance tomography (MRI) is strictly contraindicated if the intraocular foreign body is of metallic origin.

There should be a concern if the patient does not report that their status is stable or improving. Reevaluate the ocular surface for additional foreign bodies, non-healing defects, or ulceration. Repeat Seidel testing. Reevaluate the anterior chamber for shallowing, pupillary disfigurement, lenticular opacities, hyphema, hypopyon, or increased cells and flare. 

Corneal foreign bodies (FB) of organic, vegetative, or metallic origin are particularly concerning. These are more likely to incite an aggressive inflammatory reaction.

If there is any potential of vegetative FB, then consider that there is a significant risk for developing keratitis of fungal etiology.

If the FB is of metallic origin, particularly if a ferrous material, be aware that a corneal rust ring can develop within hours of the initial trauma. Depending on the depth and location, the corneal rust ring is removable by using an appropriate burr or Alger brush.  The Alger brush, when used properly, can safely remove metallic debris and the rust ring. Ideally, the internal clutch mechanism will, with excessive pressure on the Bowman membrane, disengage the burr and prevent penetrating deeper. 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 deeper tissue is compromised. Do not risk pursuing capacious treatment leaving a central corneal scar or extensive thinning.

Clinical Significance

A corneal foreign body (FB) may present in an insidious manner or, more frequently, with an acute onset of multiple ocular symptoms. Symptoms include hyperemia, eye pain, decreased visual acuity, blepharospasm, and photophobia. Timely removal of an FB reduces the potential for corneal compromise. The nature of the event may determine the course of healing. Small, superficial FB are easily removed with little risk of negative sequelae. Foreign bodies more deeply embedded or located centrally are likely to result in visually-significant scarring. The external debris may be contaminated inoculating the eye with 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 are signs suggestive of 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.

Enhancing Healthcare Team Outcomes

When the care team is counseling patients, they should reinforce the need for protective eyewear to diminish the risk for ocular trauma. Evidence of prior corneal scarring suggests previous injuries due to similar behaviors in the past. Occupational settings may contribute to eye injuries. Others may have risky hobbies or live in environments that may lead to corneal foreign bodies (FB). Any monocularly functioning patients should be prescribed full-time protective eyewear and strongly encouraged to use it to protect their only seeing eye.[14] FB and rust ring removal can be accomplished with different techniques, most popular the small gauge needle or the ophthalmic burr.  Studies have shown that while the ophthalmic burr results in complete removal of the FB and faster healing, it may create deeper and more extensive scarring as well.[15]  A study in 2017 reported that sending patients with a corneal injury home from the emergency department with a 24 hour supply of topical anesthetic (tetracaine) is safe.[16] The same study also reported that there was a wide confidence interval in these results, indicating that there were significant complications in a small percentage of patients.  Therefore, to enhance healthcare outcomes, it is recommended to not provide patients with topical anesthetic.  Pain may be controlled adequately and more safely with a bandage contact lens, and a scheduled follow up visit to assess corneal healing. Healthcare team outcomes are improved when the team has the ability to rule out a positive Seidel sign as well as other signs of intraocular penetration of the foreign body such as endothelial, iris, and crystalline lens damage and/or the observed presence of an intraocular foreign body. The team will need to assure that a careful slit lamp exam and a dilated fundus exam are done in a timely fashion.


References

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