21 Recurrent epithelial erosion
Dogs and cats with recurrent epithelial erosions typically present with mild conjunctival hyperaemia, increased lacrimation and slight blepharospasm in the affected eye. Breeds typically presented include boxers and corgis although any middle-aged dog can be affected, including crossbreeds. Burmese and Persian cats tend to be over-represented compared to the general feline population.
Commonly only one eye is affected but occasionally both eyes are involved at the same time. The degree of discomfort is variable – some patients do not seem sore, while others try to rub the affected eye from time to time. A few patients are particularly uncomfortable although this is quite uncommon. There may be a change in appearance of the eye – the cornea is sometimes slightly oedematous, giving a grey–blue cloudiness to the ulcerated area while some conjunctival hyperaemia is inevitable. Sometimes a secondary bacterial infection can develop and in these cases the ocular discharge will change from serous to mucopurulent in nature and the owner might present the patient because of the discharge.
Owners usually notice the slight redness and watering for several days before bringing the patient to the surgery. Unfortunately, they sometimes wait until the disease has been complicated by a bacterial infection – they do not worry about the increased lacrimation or redness until the discharge becomes purulent! Sometimes there is a history of possible trauma – running through the bushes for example – although this is by no means necessary for the ulcer to develop. If the patient has suffered from similar problems in the past, the owners are more likely to present their pet sooner for evaluation. Often the disease is recurrent in one or both eyes.
A full ophthalmic examination should be performed on both eyes. Conjunctival hyperaemia and increased lacrimation are the typical abnormalities present. The degree of blepharospasm is variable. As with all patients presenting with ocular surface disease, Schirmer tear test readings should be taken from both eyes. It is usual for the affected eye to have a higher reading. The patch of ulceration might be visible with the naked eye but it is important to test both eyes with fluorescein – and to flush the excess away properly with sterile saline. Typically the ulcer has an irregular outline with under-run edges – the fluorescein leaches under the loose epithelium (Figure 21.1). This lip of non-adherent epithelium is pathognomonic for the non-healing ulcer. Also by their nature these ulcers are extremely shallow – it is only the epithelium that is denuded, the stroma remains intact.
There may be evidence of corneal vascularization – fine branching vessels from the limbus nearest to the ulcer (Figure 21.2). If the case is presented late in the course of the disease this vascularization might be abundant, producing an obvious granulation reaction and the owner’s complaint of a red eye. If the case is complicated by secondary bacterial infection, the discharge will be mucopurulent in nature – although usually it is purely serous. Occasionally corneal oedema is present in the ulcerated area and adjacent tissue but this is not usually a particularly obvious clinical sign. Normally there is no intraocular involvement, although mild miosis might be apparent due to a reflex uveitis. This is more likely in long-standing cases, or when the patient seems particularly uncomfortable – the spasm of the iris constrictor muscle will cause ocular pain.
Minimal work-up is required since the diagnosis should be obvious from the presenting signs and the findings of the ophthalmic examination. As mentioned in the above paragraph on ophthalmic findings it is important to test both eyes with fluorescein. It is also sensible to check for foreign bodies, particularly behind the third eyelid or in the conjunctival fornix, and especially if the ocular discharge is purulent in nature. It is not usually necessary to perform culture and sensitivity testing on the ocular discharge unless it is mucopurulent or purulent in nature.
Nursing the patient with a non-healing ulcer usually involves topical medication. Hospitalization is not usually required and, as such, the nurse should ensure that the owner is competent at putting in the drops or ointment, and is able to medicate frequently enough. Patients should not be allowed to rub the eye(s) – they are most likely to do this immediately after the application of topical medication and should therefore be distracted for a few minutes afterwards. Elizabethan collars are not routinely required. If the patient persistently tries to rub they might be necessary but most animals are fine without – providing that they have adequate analgesia and are closely monitored after the application of topical medication.
Recurrent epithelial erosions have a variety of synonyms – non-healing ulcer, indolent ulcer, boxer ulcer, refractory corneal ulcer, spontaneous chronic corneal epithelial defect (SCCED) and so on. As the names imply, they are shallow, slow to heal and have a tendency to recur. The condition was originally described in the boxer, and although it remains most commonly seen in this breed it can occur in any breed of dog, particularly middle-aged and older patients. It also occurs in cats – Persians and Burmese breeds are presented more commonly than domestic types.
The condition is thought to represent a corneal epithelial dystrophy characterized by epithelial basal cells which produce an abnormal basement membrane and have reduced numbers of hemidesmosomes for attachment. These two abnormalities have been demonstrated in boxers affected with epithelial erosions. The normal attachment of the epithelium to the underlying stroma is dependent both on the basement membrane (augmented with anchoring fibrils) and on hemidesmosomes, and as such it is easy to understand how abnormalities with both of these structures could lead to epithelial non-attachment. It also explains why the ulcers often develop in the absence of trauma or any other inciting cause, and contributes to the problems sometimes encountered in achieving proper healing.
Histologically, affected dogs have separation of their basal epithelial cells from the underlying basement membrane and there are multiple layers of cells in the adjacent lip of non-adherent epithelium. Both hyperplastic and degenerate cells can be present in this lip of abnormal epithelium, together with inter- and intracellular oedema. The abnormal basement membrane can have splits within it and the adjacent stroma can also contain abnormal hyalinized acellular components.
On initial diagnosis of a recurrent epithelial erosion or refractory corneal ulcer (or whichever name you choose!) it is important to explain the condition fully to the owners. If they are aware of the nature of the disease, including the expected healing time, potential complications and various treatment options available, they are more likely to cooperate with treatment plans and improved results can be expected. If not fully appraised, owners become dissatisfied as the condition can drag on for weeks, or even months, and in this situation owner compliance is likely to be poor.
Show the owner the ulcer and its progress. It is easy for them to see the fluorescein-stained lesion and it also helps with their understanding. When they feel involved in the monitoring of the case, compliance with treatment will be improved.
In cats with recurrent epithelial erosions it is important to warn the owner of the risk of sequestrum formation. This can occur following any chronic feline ulcer and usually requires referral for surgical removal via superficial keratectomy together with conjunctival grafting or corneoscleral transposition.
There are various treatment options available for recurrent epithelial erosions. Normally these will consist of initial medical management but can progress to surgical procedures of varying complexity depending on the response to treatment.
Debridement of any loose epithelium is fundamental to achieving healing. This is normally performed under topical anaesthesia and should be performed on initial presentation – the characteristic lip of non-adherent epithelium needs to be removed before normal adhesion can occur. If the patient is fractious or the eye particularly painful, then sedation might be required; however, this is rarely necessary. One drop of topical anaesthetic is applied (e.g. proxymetacaine) and repeated 5 minutes later. The patient’s head is held still and a dry, preferably sterile, cotton bud is used to remove all loose epithelium. The cotton bud can be gently rubbed over the ulcer and rolled at the edges to pull off the thin, loose tissue (Figure 21.4). Each time the tip becomes moist it should be replaced with a new cotton bud. Normally three to five are required to fully debride the ulcer. This will enlarge the ulcer significantly and it is important to explain this to the owners – it is quite usual to double or even triple the size of the erosion just with simple debridement.