Specialty Spotlight: Infected Corneal Ulcers
Keith Montgomery, DVM, DACVO
As the summer weather heats up, our canine and feline patients are more active outdoors, and we see an increase in the number of traumatic corneal ulcers as well as other traumatic eye injuries. Bacterial corneal infections also become more prevalent with increasing temperatures and humidity. Common bacteria that infect the cornea include Staphylococcus, Streptococcus, and Pseudomonas spp. Clinical signs of a bacterial corneal infection include cellular infiltrate, delayed corneal healing, loss of corneal thickness, and active corneal melting (keratomalacia).
Antibiotic therapy is the cornerstone of medical therapy for uncomplicated as well as infected corneal ulcers. Neomycin-polymyxin-bacitracin is an appropriate ophthalmic medication for antibiotic prophylaxis for uncomplicated corneal ulcers; however, infected corneal ulcers warrant broad spectrum antibiotic therapy that includes fluoroquinolones and / or combination medical therapy (e.g. tobramycin and cephalosporin ophthalmic preparations). Both antibiotic spectrum and corneal penetration should be considered when making treatment recommendations for infected ulcers. Depending on the severity of corneal infection, treatment with topical antibiotics as frequent as every 1 – 2 hours may be necessary. Antibiotic therapy should also be directed based on results of corneal cytology and / or aerobic culture results.
Corneal melting can progress rapidly with certain types of corneal infections and result in deep corneal ulcers or descemetoceles in as soon as 24 – 48 hours with or without appropriate treatment. Medical therapy directed to stabilize corneal melting attempts to neutralize collagenases released by bacteria and inflammatory cells alike. Treatment options for stabilizing corneal melting include autologous serum (as frequent as every 2 hours) as well as tetracyclines (e.g. doxycycline). Serine proteases have also been shown to potentiate corneal melting and can be stabilized by EDTA.
Pain control is also an essential component of medical therapy for infected corneal ulcers. Topical steroids and NSAIDs can delay corneal healing and potentiate corneal melting / infection and should be avoided with active corneal infection. Topical NSAIDs, in particular, create a burning sensation upon administration and increase the risk for self-trauma and objection to eye medications. Analgesia for corneal pain can be provided in the form of oral NSAIDs as well gabapentin; ciliary spasm can be relieved by atropine ophthalmic drops 1 – 2 times daily or as needed to achieve mydriasis.
As melting progresses, and the cornea becomes more fragile, an E-collar is another essential component for treating infected corneal ulcer by preventing self-trauma that can result in corneal perforation or new corneal ulcers.
Referral to a veterinary ophthalmologist is warranted for any dog or cat with an infected corneal ulcer as early intervention / aggressive medical therapy (sometimes including hospitalization with around-the-clock eye medications every 1 – 2 hours) can achieve corneal healing without surgery in some cases. However, as loss of corneal thickness exceeds 50%, surgical intervention becomes a consideration.
Factors that determine the appropriate time for corneal surgery include the size and location of the corneal ulcer, presence of active corneal melting, and the prognosis for vision with surgery. Surgical options for corneal repair in dogs and cats include conjunctival graft, ACell Vet (porcine urinary bladder submucosa) or other graft materials; frozen corneal allograft, and corneoconjunctival transposition. The factors that determine the timing of corneal surgery also determine which grafting procedures are most appropriate. As with any corneal surgery, the goal of surgical intervention is to achieve corneal stabilization while minimizing corneal opacity / scarring. Surgical intervention typically creates more corneal fibrosis as compared to medical therapy but also can have a more predictable outcome in severe cases.
– Keith Montgomery, DVM, DACVO