Keratoconjunctivitis sicca (KCS; dry eye) is a common eye disease of dogs.
This disease is characterized by inflammation of the lacrimal glands, resulting in reduced or absent tear formation and secondary bacterial conjunctivitis.
The disease results in a significant reduction in goblet cell activity and consequent tear formation, specifically sialoglycoproteins, leading to reduced mucin content of tears.
Causes of KCS include (in order of importance):
- Immune-mediated - typically bilateral and affects many breeds, often middle-aged
- Genetic (congenital alacrima) - Yorkshire Terrier, Bedlington Terrier, English Cocker Spaniel, Shih Tzu and Cavalier King Charles Spaniels . In this breed, KCS has been diagnosed soon after birth at eyelid-opening, and is associated with ichthyosiform dermatosis (dry-eye curly-coat syndrome).
- Neurogenic - often with an ipsilateral dry nose, commonly in middle-aged female dogs, trauma associated
- Secondary to diabetes mellitus, hypothyroidism, hyperadrenocorticism, gangliosidosis, canine herpes virus-1, canine distemper virus, Toxoplasma gondii, Leishmania spp and nodular granulomatous episcleritis
- Drug toxicity - etodolac, potentiated sulfonamides (sulfasalazine, sulfamethoxazole, sulfadiazine, and sulfadimethoxine), felbamate
- Meibomian gland dysfunction - Miniature Schnauzer
- Third eyelid removal associated with cherry eye (nictitating membrane gland prolapse)
The lacrimotoxic effect of sulphasalazine is permanent in many cases and it is recommended that dogs on this drug should be monitored for tear secretion at regular intervals.
Clinically affected eyes have a mucoid or mucopurulent discharge, with conjunctivitis and a dull cornea that may be ulcerated, pigmented or vascularized.
A Schirmer's tear test is usually diagnostic, with KCS eyes having < 10 mm/min of wetting. Severely affected dogs often have an STT result of 0 mm/min. Bear in mind that the mean STT in dogs decreases by 0.4 mm for every year of age.
A definitive diagnosis is usually based on histological analysis often reveals conjunctival hyperemia, mucopurulent ocular discharge, predominant lymphoplasmacytic infiltration, and acantholysis and keratinization of the ocular surface.
A differential diagnosis would include proliferative conjunctivitis and Meibomian carcinoma.
Medical treatment is the primary method of control of this disease with systemic pilocarpine (1 - 2% eye drops), broad-spectrum topical antimicrobials and 0.2% cyclosporine, 0.02% tacrolimus or 1% pimecrolimus.
Both cyclosporine and tacrolimus are effective in increasing the STT in dogs naïve to lacrimostimulants but tacrolimus should only be used as a second-line agent for short-term and intermittent use due to its carcinogenic properties.
In neurogenic KCS, pilocarpine is extended for 3 - 4 months.
Surgical treatments are indicated in severe cases, or those unresponsive to medical intervention, and include ventral punctal occlusion, tarsorrhaphy, conjunctival flaps, contact lenses, superficial keratectomy, keratoprosthesis, intraocular prosthesis, as well as parotid duct transposition and submandibular gland transplantation.
Prognosis is variable, depending on cause, but most dogs have a good response to medical treatment.
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