22 Deep corneal ulcer
Both dogs and cats can present with deep corneal ulcers. Usually the owner will notice a painful eye – blepharospasm and conjunctival hyperaemia (the ‘red’ eye). Some form of ocular discharge is inevitable. This might be purely serous and present as a very wet eye, but is often mucopurulent or purely purulent in nature. The latter is particularly a feature if the owner has failed to bring the pet into the surgery immediately – deep ulcers can be complicated by bacterial infection quite commonly. The pet might have been seen to rub the eye frequently as well.
In most cases the presentation of a deep corneal ulcer is acute in nature. The owner might have been out walking the dog in the woods and it came back with one eye closed and weeping for example. Or the cat was heard to be fighting with a neighbouring tomcat, resulting in a deep corneal scratch. Thus a history of a possible traumatic episode is very common. However, on occasion, there is no such trigger factor in the history and in these cases it is important to check the patient very carefully for other possible causes – an ectopic cilium for example.
Obviously a full clinical examination should be performed as well as concentrating on the eyes. This is particularly important if a traumatic injury is suspected. The affected eye is likely to be partially closed with the third eyelid protruding. This can make detailed examination difficult, especially if chemosis is also present (more common in cats – the conjunctival swelling can be so dramatic as to render corneal examination almost impossible). Sedation is sometimes necessary to fully evaluate the cornea, but before rushing to do this a few things can be done to improve your examination:
The ophthalmic examination should include measuring aqueous tear production. If the eye is very painful, or the ulcer is very deep and you are concerned about corneal rupture, then perform the Schirmer tear test on the fellow eye only. Acute keratoconjunctivitis sicca is an under-recognized cause of sudden onset, deep corneal ulceration in the dog (see Case example 16.2). The eye is assessed for vision, and the pupil should be checked – often some miosis is present representing a reflex uveitis and this should be addressed when formulating a treatment plan. A frank uveitis with aqueous flare or even hypopyon can be present in conjunction with deep corneal ulceration, especially if bacterial infection is present. Careful evaluation of the conjunctival sac, including behind the third eyelid, should be undertaken since foreign bodies can be retained here. Intrinsic factors causing the ulcer, such as ectopic cilia or entropion, should also be looked for (Figure 22.1).
Figure 22.1 Nasty granulating corneal ulcer associated with a large distichium on the upper eyelid. Although it is uncommon for distichia to cause ulceration, if the lash is directed straight onto the cornea and rubbing, then ulcers do sometimes arise.
The ulcer is usually obvious as a defect or crater in the cornea (Figure 22.2). It can be assessed for depth both before and after staining with fluorescein. It is important to flush out excess dye with sterile saline to prevent pooling in the defect which can confuse the interpretation of the test. The exposed stroma will retain fluorescein, while Descemet’s membrane does not. Thus a deep ulcer which does not stain is likely to suggest a descemetocoele which should be treated as an ocular emergency. If the ulcer is actually healing, then the bottom of the lesion might not take up dye if the epithelium has fully covered all the stroma. The stromal edges are likely to be more gently sloped toward the depth of the lesion rather than being almost vertical when recently ulcerated.
The depth of the ulcer is important when formulating a treatment plan. Also of importance is the presence or absence of blood vessels. These grow from the limbus towards the damaged cornea at the rate of about 1 mm per day. This can be used to determine the length of time the lesion has been present. If the blood vessels are getting close to the ulcer, then medical management might be a feasible option. Some corneal oedema is often present around deep corneal ulcers so a grey ring to the lesion is commonly seen. This should be differentiated from the keratomalacia seen in melting ulcers (see Case example 23.2). In this instance the cornea will be grey and gelatinous in appearance, and when examined from the side the outline of the cornea will be distorted (keratoconus). Blinking and tear film distribution should be evaluated in all cases of deep corneal ulcer. Brachycephalic breeds often have some degree of lagoph-thalmos, and corneal exposure combined with poor or incomplete blinking can compromise healing.
Only limited case work-up is usually required for deep corneal ulcers since the diagnosis is easily made on ophthalmic examination, and unless multiple trauma has occurred (e.g. dog fights or road traffic accidents), further systemic evaluation is not normally required. As mentioned in the section above on the clinical examination, Schirmer tear test readings should always be taken. This is particularly important if a central descemetocoele is present since acute keratoconjunctivitis sicca is an important, and often forgotten, cause for these (see Chapter 16). If there is a mucopurulent or purulent ocular discharge, a swab should be taken for bacterial culture and sensitivity. Samples for cytology should also be considered. Treatment plans can be drawn up once the specific cause of the ulcer is identified.
The treatment for corneal ulceration can be medical, surgical or a combination of both. Nursing care will be required. Frequent topical medication is usually necessary, using drops, ointments or sometimes both. Drops should always be applied before ointments if both are employed, and a minimum of 5 minutes (but ideally 10–15) should be left between different topical applications. Nurses should gently bathe any discharge from the eye using soft woven gauze swabs (not cotton wool which can shed fibres) and sterile saline. Patients should be evaluated for signs of discomfort and the veterinary surgeon in charge of the case should be informed of any change in patient comfort such that appropriate analgesia can be prescribed. Self-trauma and rubbing (either with the paws or against the bedding for example) must be avoided. By making the patient comfortable this can usually be prevented and Elizabethan collars are not always required routinely – providing proper monitoring is undertaken.
If surgical treatment is planned, the nurse will be involved in preparing the patient, including anaesthesia and surgical preparation of the eye along with liaison with the surgeon regarding the instruments and other surgical equipment necessary for the procedure. Postoperative nursing instructions, both for the time the patient is hospitalized and afterwards for the owners, should be considered.