Removal of Corneal Foreign Bodies
A corneal foreign body (FB) is an object that is superficially adherent or embedded in the cornea. The cornea is the most anterior portion of the globe and so is the part of the eye that is most frequently exposed to foreign bodies. Some of the common materials that may be embedded in the cornea include glass, metal, sand, plastic, or wood. The removal of a corneal foreign body is typical performed in an office or emergency room setting. Symptoms include foreign body sensation, pain, tearing, light sensitivity and decreased vision.
Should any foreign body become lodged in the cornea, it is important to obtain a thorough history to prepare for the procedure and provide appropriate patient care. Some questions to ask include: What? When? Where and How? The suspected material or composition is important to note as it can affect the management and prognosis. For example, an iron foreign body will start forming a rust ring after four to six hours of being lodged in the cornea. Injuries caused by vegetable matter or soil are more likely to get infected by fungus or bacteria. Knowing the mechanism of the injury is important in eliciting the force with which the FB entered the cornea and determining the need for any additional testing to evaluate for possible ocular perforation and intraocular foreign bodies. Additional tests include ocular B-scan ultrasound, thin cut orbital CT scan, and gonioscopy. Tetanus prophylaxis may be indicated in certain patients.
After obtaining a detailed history, the patient should have their best corrected visual acuity checked, followed by a thorough slit lamp examination. The location, size, depth and likely composition of the foreign body should be noted. Fluorescein may be used to highlight a FB and any associated epithelial defects. The eyelid fornices should be everted and swept, to reveal any additional foreign bodies.
Most corneal foreign bodies can be successfully removed at the slit lamp. Corneal FBs should be removed safely and in a timely fashion to minimize the risk of infection, inflammation, scarring, and subsequent vision loss. If not removed promptly, the foreign body can get pushed progressively deeper into the cornea, sometimes resulting in delayed corneal perforation. Glass and fiberglass FBs are generally well tolerated in the corneal stroma and can occasionally be monitored if the removal would be thought to cause more damage.  Foreign bodies that are deeply embedded or that may risk corneal perforation should be removed in the operating room.
The patient’s ocular surface should be anesthetized with topical anesthetic such as ophthalmic proparacaine hydrochloride 0.5% or tetracaine hydrochloride 0.5% to allow for removal without any additional pain or discomfort for the patient. The upper and lower eyelids can be gently held open with the examiner's fingertips and the patient can be asked to fixate on a target. In most instances, a 25- or 27-gauge 5/8” needle can be used to lift the FB from the corneal surface. . The eye should be approached at an oblique or tangential angle to avoid inadvertant corneal perforation. A jewelers forceps may be the preferred instrument for removing plant or vegetable mater, needle-like embedded foreign bodies, or superficial foreign bodies that are adherent to the corneal surface. A magnetic spud can be used to remove metallic foreign bodies and a moist cotton tipped applicator can be used to remove superficial, loosely adherent foreign bodies. Occasionally, irrigation is used to dislodge multiple small particles.
After removal of a metallic foreign body, there might be a brownish-orange rust ring remaining which can be lifted with a needle or jeweler’s forceps. The Alger brush is a battery powered burr that can also be used. The goal is to remove as much of the rust as possible safely without causing too much tissue disruption or corneal perforation.
After removing a corneal foreign body, the corneal should be reevaluated for any residual foreign particles, and an assessment of the depth of the excavation and extent of the epithelial defect should be made. Final Seidel testing is indicated in cases of deep residual defects.
Patients should be placed on broad-spectrum topical ophthalmic antibiotics for one week or until the corneal surface has re-epithelialized. A therapeutic bandage contact lens can be used short-term to reduce discomfort. The lens acts as a barrier and reduces the shear forces of the eyelids against the corneal surface, minimizes the risk of epithelial breakdown and promotes healing. A bandage contact lens should be used with caution as it can promote a more infective environment and should be monitored closely. Pressure patch can be used cautiously but is usually not necessary. A short-acting topical cycloplegic drop can be used to alleviate discomfort.
The patient should be evaluated in 24 hours and again in 7 days to assess the epithelial defect and to monitor for any developing corneal edema or infection. The exact follow up and post-procedural care will depend on the nature and depth of the FB.
Foreign bodies that embed deep to Bowman's layer will most likely lead to scar formation. Scars in the visual axis can cause decreased vision, irregular astigmatism and glare. Coats white ring refers to small rings in the superficial corneal stroma which contain iron and fibrotic remnants of a foreign body. The rings are usually round, grayish white and less than 1mm in diameter. If centrally located, they can affect visual acuity. Once the inflammation has subsided they do not change, and topical corticosteroids are not effective.
- American Academy of Ophthalmology. Penetrating and Perforating Ocular Trauma. Basic and Clinical Science Course, Section 8. External Disease and Cornea. San Francisco: American Academy of Ophthalmology; 2022-2023:448-450.
- Cao, CE. “Corneal Foreign Body Removal”. Medscape. Nov 7, 2018. https://emedicine.medscape.com/article/82717-overview.
- Murchison, AP. “Corneal Abrasions and Corneal Foreign Bodies”. Merck Manual. Nov 2017.
- Primary Care Ophthalmology. "Foreign Body Removal". U Ottawa. https://www.med.uottawa.ca/procedures/slamp/body_removal.htm
- "Corneal Foreign Body". Edward S. Harkness Eye Institute. Columbia University Department of Ophthalmology. https://www.columbiaeye.org/education/digital-reference-of-ophthalmology/