Keratoconjunctivitis sicca (KCS) or 'Dry eye' is a rare eye disease of cats characterised by reduced or absent lacrimal tears. KCS may be a consequence of feline herpes viral infection, particularly following severe conjunctivitis when conjunctival cicatrization (scarring) can affect the function of the lacrimal ductules. Orbital trauma, direct trauma to the lacrimal gland and damage to the parasympathetic division of the facial nerve will affect tear production, as will removal of the nictitating glands or third eyelid.
The effects of lacrimotoxic drugs (both systemically and topically) are not as well documented in cats as dogs, but certain drugs known to be lacrimotoxic in the dog do not affect tear secretion in the cat. A proportion of old cats may have reduced tear production without obvious precipitating cause.
Feline dysautonomia, an autonomic polygangliopathy produces widespread effects on organs innervated by parasympathetic nerves and keratoconjunctivitis sicca may be one of the presenting signs, although other ocular features such as prominent third eyelids, dilated unresponsive pupils (with normal vision) may be more obvious in the acute phase. Tear replacement therapy (e.g. 0.2% polyacrylic acid; Viscotears CIBA Vision; 0.2% w/w Carbomer 940; Geltears Chauvin) will be needed to mitigate the effects of reduced tear production.
Clinical signs of KCS, whatever the initiating cause, include some or all of the following: - an increased blink rate
- conjunctival hyperaemia
- frank conjunctivitis
- dull, lack-lustre cornea
There is often only a scant ocular discharge. Early in the course of the disease the eye may look remarkably normal on brief examination and the diagnosis is easily missed if a Schirmer tear test is not performed. Affected animals have Schirmer I (STT I) tear test values of less than 8mm/min, usually less than 5 mm and values of zero are not uncommon in eyes which look almost normal. In more chronic cases corneal vascularisation, opacification and ulceration may occur and in those cases associated with chronic feline herpesvirus ( FHV) infection, ocular surface disease will be obvious.
Treatment aims to identify and eliminate the cause when this is possible, but in many cases treatment tends to be palliative rather than curative. For cases of neurogenic origin treatment consists of one drop of 0.5% or 1% pilocarpine solution given well mixed in food, usually twice daily. Unfortunately, many cats will not eat adulterated food and pilocarpine on its own is not well tolerated orally. Topical pilocarpine may have some beneficial effect, but has not been clinically evaluated.
For KCS of non-neurogenic origin, tear replacement therapy applied to the eye three or four times daily is usually the treatment of choice, although ocular inserts have also been used. Cyclosporin does not appear to be an effective treatment for cats with KCS. Occasionally, parotid duct transposition should be considered for irreversible cases, the surgery is more difficult in cats than dogs, but nevertheless is possible and succesful. Topical corticosteroids (usually dexamethasone, betamethasone or prednisolone) are useful in the initial stages of treatment if corneal vascularisation is present. However, the usual precautions apply and it is important to ensure that no corneal ulceration is present.
- Barnett, KC & Crispin, SM Feline Ophthalmology 2002 Saunders, USA