Keratoconjunctivitis sicca is a disorder of the tear
glands that results in insufficient aqueous tear production and a
correspondingly dry cornea. The tear film contains less of the aqueous
layer and more of the mucus layer. In consequence, the classic sign of dry eye
is a thick, stringy, mucoid to mucopurulent discharge.Since this type of
discharge can also be seen with conjunctivitis, dogs
with dry eye may be mistakenly treated for chronic conjunctivitis for long
periods with little or no improvement.
In a dog with dry eye, the bright, glistening sheen normally seen in the eye
is replaced by a lackluster appearance in which the cornea is dry, dull, and
opaque. Recurrent bouts of conjunctivitis are typical. Eventually the cornea
becomes ulcerated or develops keratitis. Blindness may ensue.
Dry eye can have several causes. Immune-mediated diseases appear to play a
major role. Other cases are idiopathic-that is, the cause is not known. Breeds
predisposed to dry eye include Bulldogs, Cocker Spaniels, Lhasa Apsos, West
Highland White Terriers, and others.
Some specific conditions that predispose a dog to dry eye include:
Injury to the nerves that innervate the lacrimal
glands. A branch of the facial nerve that activates the tear glands passes
through the middle ear. Infections in the middle ear can damage this branch,
affecting the tear glands as well as the muscles on that side of the face. In
this case, the opposite eye is not affected.
Injury to the tear glands themselves. Partial or complete destruction of
tear glands can follow systemic diseases such as canine distemper, Addison’s disease, and immune-mediated
diseases such as rheumatoid arthritis. Bacterial blepharitis or conjunctivitis can
destroy the tear glands or occlude the small ducts that carry the tears into
the eye. A number of sulfonamide drugs are toxic to tear glands. Tear gland
injuries may be partially reversible if the underlying cause is
Congenital absence of the tear glands is rare, but may occur in the smaller
Removal of the third
eyelid or the lacrimal gland attached to it.
The diagnosis of dry eye is made by measuring the volume of tears. The
Schirmer tear testinvolves placing a commercial filter paper strip into the
tear pool at the inner corner of the dog’s eye and leaving it for one minute to
see how much of the strip is wetted. Normally the strip should be wet to a
distance of 20mm. In dogs with dry eye, the strip wets less than 10mm (often
less than 5mm).
Treatment: For many years, the frequent application of artificial tears was
the only treatment available for dry eye. But FDA approval of ophthalmic
cyclosporin has revolutionized treatment and greatly improved results.
Cyclosporin is an immunosuppressive drug that reverses immune-mediated
destruction of the lacrimal glands.