Secrets to understanding corneal ulceration

Corneal ulcers are an erosion or wound on the surface of the cornea resulting in loss of the corneal epithelium. Corneal ulcers can be considered simple or complicated. Simple ulcers involve the corneal epithelium and typically heal within one week’s time. Complicated ulcers are defined by an ulcer that involves the stroma, persists for over one week, or becomes infected. 

Related: Get our Guide to Corneal Disease

Diagnosing a corneal ulcer 

Determining the etiology for corneal ulcerations is important for guiding the treatment plan. A full ophthalmic examination should be performed including Schirmer tear testing, fluorescein staining, and close assessment for adnexal abnormalities, palpebral fissure size, globe movement and position, trauma, or foreign material.  

Cranial nerves (CN) should also be tested to evaluate blink response (CN V and VII) and if the affected eye is visual and light responsive with menace and pupillary light reflex (PLR) testing (CN II and III). If a primary cause is noted for the ulcer, it will likely increase the risk of the ulcer becoming complicated or indicate the need for referral for additional therapeutic procedures in the future (i.e. adnexal surgery, diamond burr debridement, dry eye management, conjunctival grafting).  

Careful attention to fluorescein stain uptake patterns will also indicate if referral is necessary. Superficial ulcers have distinct borders and show positive stain uptake on the “floor” of the ulcer. As ulcers become deeper, the walls will have positive stain uptake with occasional diffusion into the nearby stroma, creating less distinct margins. Continuing to progress, descemetoceles will not stain at the center of the ulcer, though the stroma surrounding the defect will show positive stain uptake.  

An ulcer at any depth should be examined for possible infection. Signs of infection can be as mild as a subtle yellowish green discoloration surrounding the defect to loss of rigidity of the corneal surface resulting in a dissolution of the stroma ventrally (melting corneal ulcer). 

Simple ulcers 

If no persistent inciting cause is found, or is removed (i.e. superficial foreign material), treatment may be initiated for simple, superficial corneal ulcers. Broad spectrum topical antibiotics every 6 hours (neomycin, polymyxin B, bacitracin), pain relief via topical atropine once daily, oral pain medications (NSAIDs or gabapentin), tear stimulants if warranted, hyaluronic acid tear supplements, and an E-collar to prevent self-trauma.  

Re-evaluation is recommended within 5-7 days for superficial ulcers or sooner if the owner notes worsening signs at home. If the ulcer is not healed, refer for further evaluation for anatomical abnormalities (ectopic cilia, palpebral fissure size, globe and eyelid conformation), more aggressive medical management, debridement of indolent ulcer, or possible surgery if the ulcer has progressed. 

Complicated ulcers 

Referral to a board-certified ophthalmologist is recommended for deep stromal ulcers, descemetoceles, and melting corneal ulcers. Referral will allow for closer monitoring and aggressive care including collecting samples for culture and sensitivity to adjust medical management as the ulcer is monitored if surgical intervention is not initially warranted. Surgical intervention is beneficial for stabilizing stromal ulcers affecting greater than half of the corneal thickness, descemetoceles, melting corneal ulcers, or already perforated globes. Perforation can be identified by visualizing synechia in the anterior chamber involving the defect or bulging of the iris (iris prolapse) as it aids to plug the corneal defect. These lesions are intricately repaired with various corneal grafts using surgical microscopes.   

Owners should be counseled on the risks for rapid progression if treating complicated ulcers medically. Follow up should be scheduled within 24-48 hours of initiating aggressive treatment to monitor for corneal perforation. Antibiotics with additional gram negative and bactericidal coverage (fluoroquinolones, cephalosporins, aminoglycosides) should be used in complicated ulcers.  

Application every 2-4 hours for very deep ulcers in the initial 24-48 hours is recommended along with avoiding ointments due to the risk of uveitis if corneal perforation occurs. Anticollagenase products should also be added to this protocol. Topical serum every 2-4 hours acts locally to prevent the proteolytic properties of bacteria while oral doxycycline (10mg/kg/day) acts systemically for its antibiotic, anti-inflammatory, and anti-collagenase properties. Both will act to prevent worsening infection and a melting corneal ulcer. Hyaluronic acid containing tear supplements can also be used to improve healing.  

References 

Gelatt, Kirk N. Veterinary Ophthalmology. Blackwell, 2013. 

Gelatt, Kirk N., and Janice P. Gelatt. Veterinary Ophthalmic Surgery. Saunders Ltd., 2011. 

Maggs, David J., et al. Slatter's Fundamentals of Veterinary Ophthalmology. Saunders Elsevier, 2008.