Chapter 160. Corneal Rust Ring Removal

Corneal rust rings occur commonly when metallic foreign bodies become embedded in the cornea. Removal of the rust ring is imperative to avoid permanent staining of the cornea, persistent inflammation, or disruption of corneal integrity (necrosis) with loss of stromal substance.1–3 Two techniques for the removal of rust rings are discussed: hypodermic needle extraction and corneal burr drill removal. The use of topical deferoxamine as a chemical chelator should only be used by an Ophthalmologist and is mentioned only for the sake of completeness.

The cornea is approximately 0.5 mm thick. It is comprised of five layers (from outer to inner layer): epithelium, Bowman's membrane, stroma (largest layer), Descemet's membrane, and the endothelial layer which lies directly over the anterior chamber. Corneal rust rings are formed from the oxidation of iron present in metallic foreign bodies. As little as 3 hours of corneal contact are required to form the brown stain of a rust ring.1

All corneal metallic foreign bodies require prompt removal to avoid the possibility of rust ring formation. A rust ring requires complete removal in a timely fashion in order to avoid the damaging effects of rust on the cornea. While foreign bodies should be removed in the Emergency Department, the rust ring can be left for the Ophthalmologist to remove within 24 to 48 hours if the Emergency Physician does not feel comfortable removing the rust ring.

Corneal foreign bodies and rust rings that are located in the direct axis of vision can cause permanent visual disturbances if improperly removed.2 Consult an Ophthalmologist before removing these, as they often prefer to remove them. Do not attempt to extract a rust ring if the patient is a young child, confused, or uncooperative as this can result in a perforated globe. These patients may require the use of intravenous sedation, procedural sedation, or general anesthesia to extract the rust ring.

• Slit lamp
• 25 or 27 gauge needle
• Tuberculin syringe with a needle
• Burr drill
• Burr bits
• Topical ocular anesthetic agent (e.g., proparacaine or tetracaine)
• Topical ophthalmic antibiotic
• Cycloplegic agents (e.g., cyclopentolate, homatropine, or tropicamide)
• Ringer's lactate solution or normal saline
• Fluorescein strips or liquid
• Wood's lamp (if slit lamp is not available)
• Eidolon BLUMINATOR® (Eidolon Optical LLC, Natick, MA) (if slit lamp is not available)

Having the availability of a slit lamp is preferred when removing a corneal rust ring. There are alternatives if a slit lamp is not available or the Emergency Physician does not feel comfortable with using a slit lamp. The Wood's lamp can provide the appropriate blue light required for fluorescein staining and rust ring removal. This portable device has a built-in magnification lens. It has several disadvantages including having to be plugged into an outlet, an awkward shape, and a heaviness that must be balanced while using it. A newer device is the Eidolon BLUMINATOR®. It is small, hand-held, self-contained, battery powered, and includes a 7× magnification lens.

Explain the procedure, its risks, and benefits to the patient and/or their representative. Obtain a signed informed consent to perform this procedure. Apply a topical ocular anesthetic agent into the affected eye. Determine the patient's visual acuity in the affected eye. Seat the patient at the slit lamp with their head firmly in place to avoid any unexpected movement (Figure 160-1). Examine the eye via the slit lamp and rule out the possibility of an intraocular foreign body with a corneal perforation. Perform a complete eye examination to rule out any other ocular problems. Remove the foreign body, if still present, with the hypodermic needle or tuberculin syringe. Refer to Chapter 159 for the complete details regarding corneal foreign body removal. The rust ring will often be removed simultaneously with the metallic foreign body. Make an attempt to remove the rust ring if it remains after removal of the foreign body.

Manual Extraction

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.

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.

Delayed Removal

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.

Chemical Chelation

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.

Measure and document visual acuities before and after the procedure. Consult an Ophthalmologist if the postprocedural visual acuity is different from the preprocedural visual acuity.

A corneal defect resembling a corneal abrasion will be present after the rust ring is removed. The defect is usually larger than the original foreign body and should be treated as a typical corneal abrasion. Apply topical ocular antibiotic ointment in the eye. The use of an eye patch is controversial but considered by most as unnecessary. Instruct the patient not to operate a vehicle. Administer cycloplegics to alleviate pain from an actual or potential anterior uveitis.2 Oral analgesics are appropriate in cases of persistent discomfort. Consider prescribing topical nonsteroidal anti-inflammatory drugs (e.g., bromfenac, diclofenac, or ketorolac) for pain relief. Refer the patient to an Ophthalmologist for reexamination in 24 hours. The patient requires daily follow-up and corneal staining to ensure proper healing.12

Instruct the patient on the importance of safety goggles.5 Many eye injuries occur while at work due to failure to comply with wearing eye protection, resulting in a significant loss of working hours.5,9,10 Take the time that is necessary to explain the importance of wearing safety goggles if the injury occurred while at work, gardening, or participating in hobbies (e.g., woodworking, drilling, and auto repair). The prevention of ocular foreign bodies and rust rings is preferable to treating them.11

Abandon multiple attempts at removal of the rust ring to avoid severe ocular injury and the potential for violation of the anterior chamber if the depth of the rust cannot be determined or if repeated debridement is unable to completely remove the rust ring. The eye can be left unpatched for 24 hours and the patient referred to an Ophthalmologist for definitive removal the following day in these situations or in cases of hesitancy in removing a rust ring. Delayed removal is often easier than the initial attempts due to further oxidation and injury of the corneal epithelium resulting in “softening” of the rust. The “softened” rust ring is easily scraped out in 24 to 48 hours.2 If not completely removed, the rust ring can lead to chronic inflammation, corneal necrosis, corneal vascularization, or permanent scarring.3

Removal of corneal rust rings is imperative in order to avoid permanent ocular injury. It is best accomplished with a small gauge hypodermic needle or with an electric burr device. An alternative approach is to leave the rust for delayed removal by an Ophthalmologist in 24 hours when the rust has “softened.” It is essential to completely remove the rust ring to prevent future ocular morbidity. The procedure is simple to perform with readily available equipment.