Putting an End to Your Frustration
Corneal ulceration, or a break in the corneal epithelium, can occur for a variety of reasons. Common etiologies include trauma, entropion, ocular foreign bodies, and dry eye disease. Most corneal ulcers are superficial and non-infected; with appropriate therapy they typically heal in 3 to 5 days, depending on their initial size.
Ulcers that persist beyond 5 to 7 days with little improvement despite therapy are considered refractory. If the ulcer worsens in size or depth, these cases are considered complicated, most likely by infection or softening of the cornea (keratomalacia), and require much more aggressive therapy than a refractory ulcer.
Disorders Associated with Chronic Corneal Ulceration
Refractory ulcers typically result from an unresolved underlying etiology. A thorough history, physical examination, and ocular examination must be performed to exclude possible causes of delayed healing before treatment choices are made. Common disorders associated with refractory corneal ulceration include adnexal disease such as entropion or ectopic cilia, corneal exposure such as with exophthalmos, facial nerve paralysis, or abnormal eyelid conformation, keratoconjunctivitis sicca (KCS), corneal edema due to endothelial degeneration or dystrophy, and corneal accumulation of lipid or mineral.
In middle-aged to older patients (typically 8 years or older), indolent ulceration and spontaneous chronic corneal epithelial defect (SCCED) are the most common reasons superficial ulcers fail to heal. Boxers and golden retrievers are more commonly affected than other breeds. No matter the cause of the initial ulcer, SCCEDs fail to resolve due to abnormal corneal healing from lack of adhesion of the epithelium to the underlying stroma. This is due not only to a deficiency in adhesion molecules but also to development of acellular material within the ulcer bed that physically blocks new epithelial cells from attaching.
SCCEDs are diagnosed by their clinical appearance and are always superficial (only involving loss of epithelium and not creating a divot) and not infected. Patients are often painful with variable amounts of blepharospasm and tearing. Also, chronicity may lead to development of corneal blood vessels growing toward the ulcer. The key feature of a SCCED is a loose lip of epithelium around the edge of the ulcer. To confirm, apply a drop of topical anesthetic to the corneal surface and use a sterile cotton tip applicator to gently wipe the ulcer edge. Normal epithelium should not peel away or move. Fluorescein stain may also seep underneath the loose epithelium, creating a notable feathered edge to the staining pattern.
Identify and treat the underlying cause or complicating factors before treating the ulcer. For example, a 1-year-old dog may develop a persistent corneal ulcer as a result of entropion and eyelid hair contact with the cornea. Placement of temporary eyelid tacking sutures to pull the eyelid into a more normal position is important to facilitate healing. Once the ulcer is healed, the tacking sutures can be removed and the patient reevaluated to determine if more permanent eyelid surgery is warranted. Young dogs can also develop ectopic cilia, or abnormal hairs that protrude from the conjunctiva lining the eyelid. When the animal blinks, these cilia contact the cornea and create ulceration. Surgery, typically under an operating microscope, is required to remove the ectopic cilia and allow the ulcer to heal. Patients with dry eye disease often require topical cyclosporine or tacrolimus in addition to topical ophthalmic gel or ointment lubrication to allow ulcer resolution.
All refractory ulcer patients should receive appropriate topical broad-spectrum antibiotic to prevent infection of the ulcer. Topical atropine solution or ointment can provide pain relief from ciliary body muscle spasm and miosis. Teach clients to apply watery drops before oily drops before gels before ointments and to wait 5 to 10 minutes between applications of different medications. This helps ensure each medication reaches the corneal surface and will not be diluted or blocked by subsequent therapies. Oral NSAIDs, if safe for the patient, can be used for several days to provide additional analgesia.
If corneal exposure is a complicating factor, a partial temporary tarsorrhaphy may be performed to decrease the size of the eyelid opening. This is best performed laterally as the patient may still be able to protect the medial cornea by retracting the globe and elevating the third eyelid. A partial closure will allow the cornea to be monitored and medication to be applied. A third eyelid flap is not recommended as it provides no nutritive or structural support to the eye, may cause irritation, and prevents close monitoring of the ulcer.
Corneal ulcer patients should wear an appropriately fitted, hard plastic e-collar at all times to reduce the likelihood of self-trauma as well as the chance of secondary infection. Explaining the purpose of the e-collar is paramount for client compliance, as is making sure the fit is appropriate to allow eating and drinking while protecting the eye(s).
Treatment of SCCEDs
Middle-aged to older dogs with SCCEDs require corneal debridement in addition to the recommendations above in order to achieve healing. You must be certain of your diagnosis before attempting a corneal debridement, which can cause a deep ulcer to perforate or drive infection deeper into the cornea if performed inappropriately. Consult with an ophthalmologist if you have any questions. Corneal debridement can be performed on the awake patient with the help of an experienced assistant to provide head and body restraint or under sedation, whichever is your preference.
The cornea should be gently rinsed and disinfected with 1:20 up to 1:50 dilute betadine solution before applying topical anesthetic. Mechanical debridement with a sterile, dry cotton-tip applicator is performed next, applying mild pressure in sweeping or circular motions targeting the ulcer bed, edges, and adjacent cornea to remove any nonadhered epithelium. The ulcer often becomes a few millimeters larger in this stage, which is important to determine the true extent of abnormal tissue. Once the cotton tip applicator becomes moist, it often loses friction with the cornea and should be discarded. Repeat the process, utilizing a new dry sterile swab as necessary until no further tissue can be removed. Subsequently, a grid keratotomy or diamond burr debridement can be performed, making sure to treat the entire ulcer bed as well as 1 to 2 mm past the edge of the ulcer. Recent studies describing diamond burr debridement and grid keratotomy report a >90 percent healing rate in 10 to 15 days following a single treatment. Punctate keratotomy has fallen out of favor among ophthalmologists due to the development of safer alternatives, such as the diamond burr. It is important to avoid contacting the eyelids or third eyelid with your needle or burr tip. If contact occurs, use a new needle or burr tip to avoid seeding bacteria into the freshly debrided cornea.
A contact lens can be placed after the procedure to provide additional corneal protection. Recent studies have shown that patients given a contact lens after debridement had faster healing rates and improved comfort than did those with debridement alone. Retention of contact lenses on the ocular surface may be a problem, however, especially in brachycephalic dogs.
Topical tetracycline ointment has been associated with faster healing times in SCCED patients, possibly due to anti-inflammatory properties, and is an excellent choice for antibiotic. Application three times daily is typically sufficient to help prevent infection.
Recheck in 7 to 10 days should reveal improvement if not complete healing. If the patient has not improved, it is important to repeat a thorough examination to rule out complicating factors. SCCED patients may require additional keratotomy procedures before the ulcer completely heals. As secondary infection can occur at any time, if the ulcer worsens it is imperative to alter therapy and avoid further corneal debridement. Cases that continue to be refractory may require superficial keratectomy surgery to achieve complete resolution.
Refractory Corneal Ulcers in Other Species
It is important to note that, although other veterinary species can develop refractory corneal ulcers, SCCEDs and their management are unique to the dog. The most common cause of chronic corneal ulceration in cats is infection with feline herpesvirus. Both grid keratotomy and diamond burr debridement in the cat can predispose to corneal sequestrum formation and therefore should not be performed. Rather, appropriate use of antiviral medications such as topical cidofovir or oral famciclovir is a safer alternative in these cases. Chronic corneal ulceration in horses can often be due to equine herpesvirus or fungal infection. Therefore, corneal culture and cytology may be beneficial to dictate treatment. Examining the undersides of both eyelids and the posterior aspect of the third eyelid for foreign bodies is also important in the horse. Rabbits may develop chronic corneal ulceration similar to that in dogs and often equally frustrating to manage. Owing to their very thin cornea, treatment options in rabbits are often limited. Consultation with an ophthalmologist is recommended in these cases.
For more information about managing chronic corneal ulcers in your patients, please do not hesitate to contact the University of Illinois Ophthalmology Service either by phone or via our consult email: email@example.com. Every effort is made to return consult calls and emails the same day or within 24 hours.
—Dr. Katie Fleming
Photo: Refractory corneal ulcer in a Boxer. (Photo by Joel Mills.)