Dry eye, medically known as keratoconjunctivitis sicca (KCS), is a disorder of the tear glands. Specifically, there is inadequate tear production and a resulting dry cornea.
In dogs, tears are secreted by two lacrimal glands, one situated just above the eye and another in the third eyelid.
Tears are made up of three components: a superficial oily layer, an inner mucoid layer, and a watery layer. This watery layer accounts for 95% of the tear volume.
In dog dry eye, there is an insufficient production of the watery layer while the other two layers continue to be produced. As a result, the affected eye becomes irritated, and the conjunctival tissues becomes red. A thick, stringy, mucoid discharge covers the eye. The cornea will become dry and brown.
If left untreated, the dog will eventually go blind.
Causes of Dry Eye in Dogs
There are several causes of this dog eye problem.
The most common cause seems to be immune-mediated diseases, involving the destruction of the tear producing gland tissue. Other causes are not known.
Certain breeds are predisposed to dry eye. They include the American Cocker Spaniels, Bulldogs, Miniature Schnauzers, Lhasa Apsos, and West Highland White Terriers.
Some conditions that can put a dog at risk of developing dry eye include:
Injury to the Tear Glands
Tear gland injuries can be caused by diseases such as distemper, Addison’s disease, and immune-mediated diseases such as rheumatoid arthritis.
Bacterial conjunctivitis can also destroy the tear glands. A number of sulfa containing antibiotics are toxic to the tear glands as well.
Nerve Injury
Injuries to the nerves that activate the lacrimal glands can cause dry eye. A branch of such nerve passes through the middle ear; middle ear infections can damage this branch resulting in dry eye in dogs.
Removal of the Third Eyelid
Surgical removal of the third eyelid or the tear producing gland to correct the problem of cherry eye can result in dry eye.
Congenital Absence of Tear Glands
Although rare, some small breeds, such as certain lines of Yorkshire terrier, lack the tear producing gland tissue.
Symptoms of Dry Eye in Dogs
If you notice any of the following symptoms in your dog, he may have dry eye. Seek veterinary care immediately since dry eye may lead to partial or complete blindness if left untreated:
- Thick, stringy, yellowish mucoid discharge that may stick to the hair around the eye.
- Recurrent bouts of conjunctivitis.
- Repeated and excessive blinking and/or winking.
- A dry, opaque, and dull cornea.
- Eventual ulceration of the cornea.
Diagnosis and Treatment of Dry Eye in Dogs
Dry eye in dogs at its early stages resembles a case of conjunctivitis. Diagnosis by a veterinarian is therefore essential for timely and proper treatment.
Dry eye in dogs can be proper diagnosed by the use of the “Shirmer tear test”.
A commercial filter paper strip is placed inside the lower eyelid in the outer corner of the dog’s eye for one minute. The tears secreted by the eye will make the paper wet and the extent of the strip that is wetted is measured after one minute.
A distance of 15 to 20 mm or more is normal. A distance of less than 10 mm is dry. (Less than 5 mm is severely dry).
Primary conventional treatment of dry eye in dogs is the use of an immunosuppressive drug called Cyclosporin which reverses the immune-mediated destruction of the tear glands.
Cyclosporin ointment is applied to the surface of the affected eye. The frequency of application depends on the severity of the condition. The effect of this drug is not immediate and usually the dog is put on artificial-tear and antibiotic treatments while waiting for Cyclosporin to take effect.
While Cyclosporin is sometimes hailed as the most successful drug for dry eye in dogs, it does not work if the dry eye condition is caused by severe damage of the tear glands. In such cases, artificial tears (either drops or ointments) must be applied to the dog’s eyes several times a day for life.
When all else fails, a surgical procedure known as “Parotid Duct Transposition” is the last consort.
The parotid duct is a duct that is responsible for carrying saliva produced by the salivary gland to the mouth.
“Parotid Duct Transposition” involves transplanting the parotid duct up into the corner of the eye so that saliva can be delivered over the eye.
In other words, the saliva takes the place of the tears.
However, this has several disadvantages.
First, saliva is not the same as tears. For example, saliva will cause some minerals to form and deposit on the surface of the affected eye. The dog may need special eye drops to correct this problem.
Second, the volume of tears may be more than the drainage system can handle, especially when the dog is eating, resulting in facial wetting.