Corneal ulcers in cats: guidelines for managing ulcerative keratitis
Introduction
The cornea is a smooth, transparent, avascular structure at the front of the eyeball that forms part of the fibrous tunic, hence it is exposed to a lot of aggressive situations and is one of the most common reasons for ophthalmological consultations at veterinary clinics. Its main function is to transmit and refract light and provide protection to the eyeball’s contents. As it is an avascular structure, corneal nutrition depends on the aqueous humour and tear film.1
Moving inwards from the external margin, the cornea is composed of the corneal epithelium, the stroma, Descemet’s membrane and the endothelium. Corneal ulcers are the result of damage to and loss of corneal epithelium with or without progression to the stroma.2 Depending on their depth, they are classified as superficial or deep ulcers (stromal or descemetocele ulcers).
Corneal ulcers in cats: aetiology
The corneal epithelium is constantly renewed by processes such as blinking or drying. The rate of regeneration together with protective mechanisms are often enough to prevent ulcer formation and the erosion from becoming clinically significant. Ulcers occur when an imbalance arises due to insufficient protection (eyelids, tear film) or an excessive loss of the corneal epithelium.2
The most common signs of ulcerative keratitis are photophobia, blepharospasm, excessive tearing or changes in the cornea’s appearance. Superficial ulcers are very painful because they affect the external portion of the cornea which has more nerve endings, while deep ulcers are less painful but more serious as they carry the risk of a perforated eyeball.
One of the most common causes of corneal ulcers in cats is Feline herpesvirus 1 (FHV-1) infection. In fact, ulcerative keratitis is the second most frequent sign of feline herpesvirus after conjunctivitis. The entity initially appears in the form of superficial dendritic ulcers that rapidly progress, developing an irregular geography.1-3
Another common cause of corneal ulcers is trauma, both self-inflicted (e.g., scratching the eyes or rubbing with an object) or by external agents (e.g., scratches, blows, chemicals or foreign bodies). They may also be due to eyelid or eyelash problems (entropion, ectropion, trichiasis, distichiasis, ectopic cilia, neoplasms) or lacrimal insufficiency.1,2,4 Dolichocephalic and mesocephalic breeds have a more sensitive cornea than brachiocephalic breeds, so they are more likely to suffer from these ulcers.1
Corneal ulcers in cats: medical treatment
Identifying and correcting the primary cause of the ulcer is an essential step towards a successful treatment.2,5 Most ulcers are superficial and heal quickly without complications, with re-epithelialisation occurring in about 7 days.2
Broad-spectrum topical antibiotic therapy is indicated to prevent or treat secondary infections in all types of ulcer.2,5 The choice of antibiotic and frequency of administration depends on the depth and progression of the ulcer, as well as the results of bacterial cultures.5 It should be applied 2–4 times a day as prophylaxis in uninfected ulcers, while the frequency should increased to 6–8 applications a day for stromal ulcers. If there is a risk of eyeball perforation, rapid progression of the ulcer or keratomalacia, the antibiotic should be given every 1–2 hours.5 Ointments should be avoided when there is a risk of perforation, because if any ointment penetrates the eye, it will cause severe uveitis.2
Subconjunctival antibiotics are reserved for severe corneal infections when topical application alone does not elicit a satisfactory therapeutic response. Systemic antibiotics may be indicated for lesions suggestive of endophthalmitis or in the case of full-thickness corneal perforations.5 They can also be considered for cases of FHV-1 infection where topical treatment may stress the cat and therefore increase the risk of exacerbating the infection.
The prevention of self-inflicted injuries is also an important part of ulcer management, so the use of an Elizabethan collar should be considered for cats that scratch themselves or rub against objects.2 On the other hand, the use of topical atropine to induce mydriasis provides potent analgesia for the painful ciliary muscle spasms experienced by cats with reflex uveitis secondary to ulceration. Tear production should be assessed before administering atropine, given its capacity to impair output, as this could interfere with corneal healing.5
Corneal ulcers in cats: surgical treatment
While most cases of corneal ulcers can be managed medically, some require a surgical intervention. This applies to deep ulcers when they progress rapidly (e.g., keratomalacia) or do not respond to medical treatment, or when a primary cause such as entropion has been identified.6 Surgery is indicated for ulcers where two-thirds or more of the corneal thickness has been lost and those with a descemetocele given the risk of corneal perforation and subsequent loss of aqueous humour, iris prolapse and anterior chamber contamination. The presence of foreign bodies, descemetoceles and corneal perforation require emergency surgical treatment.
Some of the surgical techniques employed are conjunctival pedicle flap surgery, corneoconjunctival transposition and lamellar keratoplasty. The choice of the most appropriate procedure depends on the need to provide tectonic support and/or vascularisation.6
All cases of entropion require surgical correction and Hotz-Celsus blepharoplasty is the technique of choice. With ectopic cilia or distichiasis, which are not very common in cats, removing the offending hair follicle will resolve the problem.
Corneal sequestrum secondary to a chronic ulcer usually requires surgical excision by performing a superficial keratectomy. 6 The efficacy of a superficial keratectomy in the resolution of chronic ulcerative keratitis refractory to medical treatment has also been demonstrated.
Conclusions
Corneal ulcers are one of the main reasons for an ophthalmological veterinary consultation. Depending on the degree of corneal involvement, they can be classified as superficial or deep ulcers. Apart from identifying and treating the primary cause, most ulcers only require topical antibiotic therapy; however, some require surgery because of the depth of the ulcer or its rate of progression.
