Keratoconjunctivitis Sicca

Keratoconjunctivitis Sicca (KCS)is a condition resulting from the lack of production of the aqueous phase of the tear film. It is also known as dry eye.

Aetiology

Immune-Mediated

The most common cause in dogs. The immune system damages the glandular tissue. Dogs with KCS often have other immune-mediated diseases.

Iatrogenic

Certain drugs, including Sulphonamides, have been associated with KCS. Atropine causes a temporary reduction in tear production.

Surgical excision of the Nictating Gland has been associated with KCS later in life, with a median time for onset of signs 4.5 years after surgery.

Neurogenic

KCS occurs if parasympathetic innervation to the glands is disrupted. Possible causes include trauma, neoplasia, infection and surgical intervention. The KCS is more likely to be unilateral.

Congenital

Due to glandular aplasia or hypoplasia. More common in miniature breeds. May resolve with maturity.

Infectious

Infection with Canine Distemper Virus may result in temporary or permanent dysfunction of the glands. Leishmania can also cause KCS, as can any chronic infectious process that results in fibrosis of the glands.

Signalment

Dogs over 10 years old are at greater risk of KCS due to senile atrophy of their glands. Boston Terriers, Cavalier King Charles Spaniels, English Bulldogs, English Springer Spaniels, Lhasa Apsos, Minature Schnauzers, Shih Tzus, West Highland West Terriers and Yorkshire Terriers are all consider predisposed.

Clinical Signs

A thick mucoid and mucopurulent discharge is the most consistent sign of KCS. It often adheres to the eyelids. The conjunctiva may be thickened, hyperemic and chemotic.

Blepharospasm may occur to a variable degree. Corneal ulceration often occurs, and may not heal as well as expected. Corneal Vascularisation and Pigmentation occur in chronic cases, leading to vision loss.

A dry, lusterless cornea is considered pathognomic for KCS, but only occurs in 25% of cases.

Clinical signs can wax and wane, and are often worse at certain times of the year, such as hot and dry periods or in winter when humidity is low.

Diagnosis

Schirmer Tear Tests are used to diagnose KCS. Normal values are in excess of 10mm. KCS should also be suspected when values are less than 15mm in conditions where excess tear production is expected, such as corneal ulceration.

Consideration should be given to ruling out other conditions that have been associated with KCS, including Hypothyroidism, Diabetes Mellitus and Polyarthritis.

Treatment

Medical Therapy

Medical therapy is normally used first for KCS, with surgical treatment only used if there is a poor response to medical therapy.

Cyclosporine

Cyclosporine is believed to help manage KCS by reducing immune-mediated destruction of the gland and by stimulating tear production by binding with prolactin receptors. Once treatment is started, tear production should be tested after a month. If there is a good response the dose may be tapered.

Tear Substitutes

A range of human tear substitute products may be used in dogs. Individuals react differently to different formulations so authors recommend trialling different preparations to see which gives the best clinical response.

Pilocarpine

May be more effective in neurogenic cases of KCS. Care must be taken to avoid systemic side effects.

Surgery

Parotid Duct Transposition may be performed in cases that respond poorly to medical treatment.

Control

KCS cases secondary to drug use, trauma or infection may resolve after 45-60 days. Other causes normally require life long therapy.

References

Maggs, D et al (2007) Slatter's Fundamentals Of Veterinary Ophthalmology (Fourth Edition) Saunders

Peiffer, Robert J, and Petersen-Jones, Simon M (2008) Small Animal Ophthalmology (Fourth Edition) Saunders