THE KERATOCONJUNCTIVITIS CASES YOU MAY HAVE MISSED OPHTHALMOLOGY Kerry L. Ketring, DVM, DACVO

If you surveyed 100 practitioners, I’m willing to bet 95% of them would say the ocular disease that causes the most suffering in their patients is glaucoma. Surveys have proven otherwise. One survey showed 4% of all had keratoconjunctivitis sicca (KCS). In a second study, 1% of all hospital admissions resulted from this dry eye condition. The incidence of dry eyes is high in many breeds. The cocker spaniel leads all breeds with 20% of all cocker spaniels affected. All of this results in KCS being a greater cause of ocular pain, blindness, and enucleation than glaucoma. Being aware of the causes of KCS, including the breed incidence, allows the veterinarian to avoid the complications of this disease. The complications of KCS, including enucleation, are preventable through diligent testing of predisposed breeds, the knowledge of other conditions that predispose to KCS, and as part of every geriatric exam.

Clinical Signs Clinical signs of early KCS include mild mucous formation and conjunctival hyperemia. Practitioners frequently misattribute these two symptoms to some type of allergy.

As the disease progresses, corneal vascularization and pigmentation develops which often leads to decreased vision.

Corneal ulcerations, most frequently axial, are not uncommon. These ulcers may lead to a corneal rupture. In early cases with borderline Schirmer tear test (STT) values, the clinical signs may wax and wane depending in part on the animal’s activity and environment. Although usually bilateral, KCS is often not symmetrical in severity.

Testing The STT is the primary diagnostic test utilized. STT I measures both reflex and basal tear production and is reported to be 15–25 mm/min in the and 10–15 mm/min in the cat.

These values may fluctuate significantly even in one individual. This fluctuation is especially common in breeds predisposed. Clinically normal cats may even have a tear production of 0–3 mm/min!

STT II is not commonly used in veterinary medicine except by ophthalmologists. STT II measures the basal tear production. This is done by first applying a drop of topical anesthetic to the eye and waiting one minute before gently drying the lower cul-de-sac with a cotton swab and then administering the test. The reported values are 6– 18mm/min in the dog and 8–12 mm/min in the cat.

Small breeds of dogs have a greater reflex tearing and larger breeds have greater basal tearing. Exophthalmic breeds require a greater tear production due to lagophthalmus and increased tear evaporation. SST values are reported to decrease with age and this is especially important to monitor in the breed predisposed patients.

A second diagnostic test is performed rarely, even by veterinary ophthalmologists. Tear film breakup time (TFBUT) evaluates the integrity of the inner most layer of the tear film. This muscin layer produced by the conjunctival goblet cells is important for tear film stability. A drop of fluorescein stain is applied to the cornea. The lids are closed briefly and then held open as the stained tear film is observed, usually with a blue light. The time from opening of the lids to the appearance of the first black dot, which represents a break in the tear film, is recorded. The TFBUT in the dog should be >20 seconds and in the cat it is reported to be 12–21 seconds. In the cat with a feline herpesvirus type 1 (FHV-1) infection, the TFBUT is reported to be more rapid. Dogs may have a STT value within limits of normal, but a rapid TFBUT and clinical signs of a dry eye. This is seen in the English and Cavalier .

Etiology of KCS The most common cause of KCS in dogs is related to a breed predisposition (Table I). Congenital KCS has been seen in the pug, Chihuahua, Yorkshire , and Cavalier King Charles spaniel. Removal of a hypertrophied gland nictitans, especially in predisposed breeds, may also cause KCS.

Drugs proven to be associated with KCS include systemic sulfonamides, phenazopyridine, and etodolac (EtoGesic® Fort Dodge). Atropine topically, as in the case of the treatment of anterior uveitis or systemically as a pre-anesthetic, can have a profound effect on tear production.

It has been suggested that other drugs, including potassium bromide, may be associated with KCS. Oral and topical antihistamines can cause decreased tear production in humans, but varies considerably with the drug and the individual. The most common antihistamine dispensed by veterinarians, diphenhydramine, at recommended dosage did not result in decreased STT values in one study.

Loss of parasympathetic innervation to the lacrimal gland associated with facial paralysis (CNVII) and loss of corneal sensation associated with trigeminal (CNV) paralysis may also lead to KCS. Decreased STT values have been seen for up to 48 hours following a general anesthetic with or without anticholinergics such as atropine. The duration and severity of the decreased tear production varies with the duration, not necessarily the type, of anesthesia.

Three endocrinopathies have been shown to be associated with decrease tear production in dogs. In one study, the normal control had a STT of 19.6 +/− 4.2. Whereas dogs with hypothyroidism (12.3 +/− 3.2), hyperadrenocorticism (14.0 +/− 4.0), and diabetes (12.3 +/− 5.3) all had significantly lower values. In all three diseases, values were low in treated and untreated individuals. Peripheral neuropathies could play a part in the decrease tear production and complicate an existing reduced STT. All three diseases have reported associated neuropathies.

The etiology of many cases of KCS cannot be determined. Based on histopathology of lacrimal glands of dogs with KCS, it is suggested most have an immunologic bases. This may even be true in the predisposed breeds. Associated immunologic diseases are a rare and inconsistent finding.

The incidence of KCS in cats is low compared to dogs. There has been a breed predisposition reported (Table 2). Cats with congenital eyelid agenesis may also have decrease corneal sensation and tear production.

Drug toxicity resulting in KCS has not been reported in cats except in the case of atropine. In my opinion, the most common cause of KCS in cats is a prior herpes infection.

Table 1. Canine Breeds Disposition to KCS English bulldog Pug Samoyed Sealyham terrier German shepherd dog Schnauzer (all varieties) Cavalier King Charles spaniel Shih tzu Chihuahua Chow chow West Highland white terrier Lhasa apso Cocker spaniel Pekingese Dachshund Poodle (all varieties)

Table 2. Feline Breeds Predisposed to KCS Abyssinian Himalayan Burmese Persian Domestic shorthair

When To Test

1. All dogs and cats listed in Tables 1 and 2 on yearly physical. 2. Both eyes in dogs presented with unilateral conjunctivitis or keratitis with or without ulcers. 3. Prior to instituting drug therapy with drugs listed above and weekly to monthly during treatment period. 4. Prior to surgery for hypertrophied glands nictitans. 5. Prior to and during treatment for anterior uveitis with topical atropine. 6. Prior to and after general anesthesia. 7. Prior to grooming in predisposed breeds. 8. All cats with conjunctivitis and/or keratitis. 9. All dogs with the previously listed endocrinopathies.