Scrape out the rust ring in a similar fashion to the removal of a metallic foreign body (Figure 160-2). Refer to Chapter 159 for the complete details regarding corneal foreign body removal. The entire area of rust stained epithelium must be completely removed without any residual rust.
Manual extraction of the rust ring.
Extract the rust ring with a corneal spud or hypodermic needle. A corneal spud is a stainless steel device that comes in a variety of shapes. It generally consists of a sharpened metal tip attached to a handle.1 It is used to lift off or to carve out a corneal foreign body or rust ring.1 Many physicians prefer to use a tuberculin syringe. It allows for better control of the needle by using the syringe portion as the grip. The author always uses a saline-filled tuberculin syringe. This allows the Emergency Physician to apply saline drops to moisten the eye as well as to flush away the rust ring after it is dislodged from the cornea. The instrument used is physician dependent. Proper explanation of the extraction procedure using a needle will often ease a nervous patient and ensure better compliance by limiting unexpected movements.
Perform the procedure under direct visualization with the slit lamp. Place the patient seated at the slit lamp with their head firmly in place against the forehead rest to avoid any unexpected movement (Figure 160-1). If a slit lamp is not available, the foreign body can be removed using the blue light of a Wood's lamp or Eidolon BLUMINATOR®. Hold the needle, or spud, between the thumb and index finger of the dominant hand as one would a pencil with the bevel facing the examiner. Stabilize the dominant hand on the patient or the slit lamp apparatus using the remaining fingers. Instruct the patient to focus their vision on a given point to avoid any eye movement.
Approximate the tip of the needle, or spud, to the rust ring with the naked eye before utilizing the slit lamp microscope in order to avoid inadvertent injury. Approach the rust ring from the periphery and not across the patient's field of vision (Figure 160-2A). Gently tease out the rust ring using the beveled edge of the needle, or spud, in a tangential direction in relation to the eye to avoid inadvertent deep puncture if the patient suddenly moves. Use the tip to gently pry the rust ring loose if absolutely necessary, but extreme care must be exercised (Figure 160-2B). Remove the loose rust ring with a moistened cotton-tipped applicator or with gentle irrigation.
Electric Burr Drill Extraction
An electric battery-powered drill equipped with diamond burrs, if available, can be used for rust ring removal (Figure 159-3). The burr bit cuts away corneal tissue very slowly. Corneal rust rings were induced in rabbits and comparisons were made between manual extraction versus electric drill extraction.1 Both were equally effective for rust ring removal, but the burr caused a deeper corneal defect. Use caution when using an electric burr device. There was no difference in corneal scarring between the two techniques. The burr drill can also be used to extract rust in the bulbar conjunctiva.4
Choose a burr size that is slightly larger than the diameter of the rust ring. Load the burr onto the drill. Grasp the device like a pencil using the thumb and middle finger. Press the finger bar on the drill with the index finger to turn on the drill and rotate the burr bit. Approach the rust ring tangentially to the eye (Figure 160-3). Gently place the rotating burr bit on the area to be debrided using short applications of one to two rotations of the burr. Lift the burr from the cornea after each application to examine the area and determine if the rust ring has been removed. Thoroughly inspect the base of the crater to ensure that it is free of rust.4 Continue the process until the rust ring is removed. Use a slightly larger burr bit if rust still remains along the periphery of the crater.
Burr drill extraction of the rust ring.
The rust ring may be removed after it ages.2,8 Allow the rust ring to remain for 24 to 48 hours. During this time the iron deposits will kill the surrounding corneal epithelial cells. The rust ring will “soften” and be easily removed in one piece with a needle, spud, or burr drill. Do not allow the rust ring to remain for longer than 24 to 48 hours, ideally 24 hours, as it can cause significant damage to the cornea.
Topical deferoxamine has been used experimentally for the nonsurgical removal of rust stains on the cornea.6 It has been shown to remove rust, though perhaps not as reliably as the methods previously described. The potential exists for resultant eye irritation, corneal ulceration, or persistence of the rust stain.6 The clinical use of deferoxamine should be limited for use only in very select situations such as children with multiple lesions or when the central axis of vision is involved.7 This technique is reserved for the Ophthalmologist and is therefore not described in this text.