Corneal Foreign Body
Small foreign bodies can become embedded in the corneal epithelial surface, as the texture of the cornea is similar to gelatin. Larger foreign bodies can cause a corneal abrasion and then leave the eye. Because of the density of corneal pain fibers in the normal eye, an abrasion and a foreign body feel the same to the patient. Blinking abrades the epithelial defect and exacerbates discomfort. Treatment should mitigate the effect of the upper eyelid on the epithelial defect to minimize discomfort and promote healing.
Corneal foreign bodies are identified most effectively by slit-lamp examination. Before removing a corneal foreign body, the clinician should assess the depth of corneal penetration. Occult intraocular foreign bodies must be ruled out when there is a history of exposure to high-speed metallic foreign bodies, typically from grinding tools and metal-on-metal hammering.
Identifying the composition of a corneal foreign body by either history or examination is important. Vegetable matter, such as leaves, thorns, bark, and dirt, presents an increased risk of fungal keratitis, so corticosteroid drops are contraindicated in patients with these types of foreign bodies, because of the risk of potentiating fungal infection. Contaminated foreign material from a hospital or medical setting may pose a higher risk of bacterial infection.
If glass foreign bodies are present, all exposed fragments should be removed. Fragments deeply embedded in the cornea are often inert and can be left in place (Fig 14-25). Careful gonioscopic evaluation of the anterior chamber is essential to ensure that the iris and the angle are free of any retained glass particles. Glass particles in the anterior chamber are indicative of a perforating ocular injury.
When an iron foreign body has been embedded in the cornea for more than a few hours, an orange-brown “rust ring” results (Fig 14-26). Corneal iron foreign bodies and rust rings can usually be removed at the slit lamp with a disposable (25-gauge or 26-gauge) hypodermic needle, after application of a topical anesthetic. A battery-powered dental burr with a sterile tip may also be utilized; however, the rotating burr can cause excessive tissue disruption and increased scar formation. A foreign body that enters the corneal stroma deep to the Bowman layer always results in some degree of scar formation. When these scars occur in the visual axis, they may result in glare and decreased vision from irregular astigmatism. Optimal management of a corneal foreign body therefore includes minimal disruption of the Bowman layer to avoid further scarring and obstruction of the visual axis.
Therapy following the removal of a corneal foreign body includes the use of topical antibiotics, cycloplegia, and occasionally the application of a firm pressure patch or bandage contact lens to help the healing process. If a pressure patch or bandage contact lens is used, the risk of infection due to the foreign body is increased and the patient should be closely monitored until this risk has passed.
Blast injuries may cause both penetrating and perforating corneal foreign bodies (Fig 14-27). For patients with blast injuries, the clinician should meticulously remove all possible foreign bodies on or near the surface of the cornea to prevent subsequent erosion of the superficial foreign bodies and accompanying discomfort.
Scott R. The injured eye. Philos Trans R Soc Lond B Biol Sci. 2011;366(1562):251–260.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.