Corneal Ulceration - Dogs and Cats
A corneal ulcer is a loss of epithelium on the surface of the cornea. It is also known as an ulcerative keratitis as there is always a degree of inflammation accompanying the loss of epithelium.
Signalment
More common in dogs than cats, as cats are less likely to suffer trauma to their corneas. Animals with large, open palpebral fissures (eg Brachycephalics) are at higher risk of corneal trauma.
Clinical Signs
Clinical signs can include signs of ocular pain, such as blepharospasm and miosis. There is often ocular discharge and an aversion to light.
Diagnosis
The ulcer may be visible on examination of the eye. Applying fluorescein dye to the eye will stain exposed layers of epithelium. If the center of a deep ulcer does not stain, this indicates the Descemet's Membrane is exposed.
Corneal ulcers often have underlying causes, which if not treated will cause the ulcer to recur. It is important to assess the eyelids fully for any entropian, ectropian, ectopic cilia or foreign bodies which may be present. Palpebral reflex and lid closure should also be checked. Consideration should also be given to testing tear production and bacterial and viral culture if appropiate.
Treatment
Ulcers can be classified into simple or complex ulcers which can help determine which treatment is needed. Simple ulcers are shallow so heal without stromal involvement and heal within seven days. Complex ulcers are deeper so heal with stromal involvement, and/or take more than seven days to heal.
Complex ulcers can be further classified into one of three categories to assist in resolving the ulcer:
- Underlying cause not identified/resolved
- Infected
- Indolent, seen only in dogs
Medical Treatment
Regardless of cause, all ulcers should be treated with a range of medications.
Antibiotics
Broad spectrum topical antibiotics should be applied. Even if the ulcer does not appear infected, disruption of the corneal epithelium predisposes to infection. Systemic antibiotics are unlikely to reach the cornea unless it is well vascularised or after conjunctival graft surgery.
Mydriatics
Exposure and stimulation of corneal nerves can result in a reflex anterior uveitis. Topical atropine is used to control this, with the dose tapered once adequate pupil dilation is achieved. Atropine should not be used in cases of keratoconjunctivitis sicca as it can disrupt tear production.
Analgesia
Systemic Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) should be administered whilst the eye is painful. Topical steroids or NSAIDs should not be applied as they may disrupt healing of the ulcer.
Preventing Self-Trauma
It is important animals do not rub at their eyes, making the corneal ulceration worse. Devices to prevent self–trauma, such as elizabethen collars can be used if necessary.
Deep Ulcers
Deep ulcers require additional therapy to resolve.
Melting Ulcers
Collagenases are enzymes produced by some bacteria, as well as degranulating neutrophils and disrupted epithelial cells and stromal cells. The enzymes can liquefy the corneal stroma, resulting in a rapidly progressive, "melting" ulcer. Bacteria commonly involved include Psuedomonas Aeruginosa, coagulase–positive Staphylococci, beta–haemolytic Streptococci and other gram–negative bacteria.
Samples for culture should be taken, and frequent topical antibiotic therapy should be applied.
Anti—collagenase therapy may be applied. This is done by harvesting serum from the patient then applying topically to the eye.
These animals can require intensive therapy so consideration should be given to hospitalisation.
Surgical Treatment
Corneal ulcers deeper than half the depth of the cornea take longer to heal due to the cornea's limited ability to regenerate, so can benefit from surgical techniques to aid healing. Techniques recommended include conjunctival grafts, temporary tarsorrhaphies and third eyelid flaps
References
Maggs, D et al (2007) Slatter's Fundamentals Of Veterinary Ophthalmology (Fourth Edition) Saunders
Peiffer, Robert J, and Petersen-Jones, Simon M (2008) Small Animal Ophthalmology (Fourth Edition) Saunders