PRESENTING SIGNS

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.

CASE HISTORY

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.

CLINICAL EXAMINATION

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:

• If the eye is painful, then a drop of topical anaesthetic can be placed and repeated 2–3 minutes later.

• If any ocular discharge is present and a swab is considered for bacterial culture and sensitivity testing, then this should be taken before the application of topical anaesthesia.

• The third eyelid can still be elevated and present a barrier to corneal examination despite numbing the cornea. By placing the patient at the end of the examination table and making them look down, the third eyelid is retracted back to its normal position. Thus if you bob down and look up to the patient, your examination is likely to be more rewarding.

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.