31 Chronic feline keratitis
Chronic feline keratitis is usually seen in adult cats and in most cases is unilateral in presentation. The owners might have noticed a discharge, a change in appearance of the eye or ocular discomfort, but often all three symptoms are reported to various degrees. Feline keratitis can be ulcerative or non-ulcerative. The former can present as superficial erosions, similar to the recurrent epithelial erosion or indolent ulcer seen in dogs, but usually with a different aetiology – primary feline herpes virus (FHV-1) is the most common cause for recurrent superficial ulcers in cats and we will concentrate on this infection when discussing feline keratitis. Other types of ulcer are usually the result of trauma, such as following a cat fight, and subsequent to other ocular diseases such as entropion, although this is far less common than in dogs. Reactivation of FHV-1 infection following a previous acute episode of ocular and respiratory disease is frequently reported. Occasionally cats can present with keratitis in addition to systemic disease and only when the latter is correctly diagnosed and treated do the ocular signs respond.
As mentioned above, FHV-1 is commonly associated with keratitis in cats and, as such, the history will often include previous ocular or respiratory disease. Rescue or re-homed cats are over-represented so questioning the owner regarding how they acquired the cat is important. Lifestyle is also relevant since outdoor cats, or those which frequently get into fights with other cats, can be at a higher risk of developing recurrent keratitis. It is common for the same eye to be repeatedly affected although in some cats both eyes can be involved, either simultaneously or at different times. Commonly the owner reports that the eye never appears totally normal but it only bothers the cat from time to time. The condition can recur following immunosuppression, for example following an unrelated illness or via the use of systemic steroids for another complaint.
In recurrent cases of FHV-1 systemic signs are usually absent but a full clinical examination should still be performed. Ocular signs of mild blepharospasm, increased lacrimation and some conjunctival hyperaemia are usually present. Schirmer tear tests should be performed before any discharge is cleaned away or samples taken. These can be elevated, normal or reduced. Conjunctival hyperaemia is normally present but chemosis is variable. Careful examination for evidence of ocular trauma or other inciting causes should be undertaken. Small corneal opacities, which may or may not stain positive with fluorescein dye, and fine vascularization are common findings. Larger superficial ulcers with irregular outlines and under-run edges are encountered and readily identified on careful examination (Figure 31.1).
Figure 31.1 Three-year-old British Blue with irregular superficial corneal ulcer. The cat had suffered from upper respiratory tract infection as a kitten and went on to develop recurrent ulcers in both eyes. Viral isolation was positive for FHV-1.
However, if FHV-1 is suspected as the cause for the keratitis then staining with rose Bengal should be considered. This is more sensitive than fluorescein at highlighting the small areas of epithelial devitalization and the demonstration of these dendritic ulcers is considered pathognomonic for FHV-1 keratitis (Figure 31.2). Careful evaluation of limbus is advised since acute herpetic infec tions in young cats will often result in limbal damage such that the neat dark line present between the clear cornea and white sclera is disrupted. Similarly, examination of the conjunctiva, especially around the nasolacrimal punctae and fornices, might reveal evidence of symblepharon (Figure 31.3), which is another frequent complication of FHV-1 and contributes to both chronic epiphora and corneal ulceration via reduced ocular and third eyelid motility as a result of the adhesions.
Figure 31.2 Right eye of a domestic short haired cat with FHV-1. Fine ‘dendritic’ ulcers are present dorsolaterally, highlighted in magenta pink due to rose Bengal staining. A mucoid discharge is adherent to the cornea and Schirmer tear test readings were 2 mm in this eye and 8 mm in the normal left eye (keratoconjunctivitis sicca can develop secondary to FHV-1 and should not be overlooked).
Severe corneal scarring with FHV-1 is usually stromal and ulceration can be a typical feature with small punctate or larger coalesced lesions. Extensive vascularization and oedema can occur. A mild reflex uveitis can be present, with miosis and some rubeosis iridis, but intraocular involvement is not an obvious part of the clinical examination.
Thorough clinical examination will lead to the suspicion of FHV-1 and should rule out other causes of keratitis such as primary keratoconjunctivitis sicca or corneal sequestrum. However, as these are often associated with FHV-1, attempts at viral isolation or polymerase chain reaction (PCR) from both conjunctival and oropharyngeal swabs are advised since the treatment protocol might be changed if positive laboratory results are obtained. Corneal scrapes can be used for PCR and are probably more sensitive than conjunctival swabs since the samples are from the area most likely to be infected with virus. Cytology can be useful to rule out differentials such as proliferative keratoconjunctivitis. Some cats with herpetic keratitis are immunosuppressed and so screening for feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) is sensible.
General principles of cleaning discharges and careful application of medications apply, with no specific considerations other than barrier nursing since these patients can be infective. Topical medication may be required on a frequent basis which can be difficult for owners to manage, so sometimes cats can be hospitalized during the initial treatment period (although the stress this induces can prolong healing times!).