Dry eye is a very common eye condition in our companion animals with higher prevalence in certain dog breeds such as English Bulldogs, Cocker Spaniels, Pugs, Cavalier King Charles Spaniels, Lhasa Apsos, Shih Tzus, and West Highland White Terriers. Most canine patients develop dry eye due an immune-mediated (auto-immune) inflammatory attack on the tear glands. Without treatment, the excessive inflammation impairs or destroys the tear glands and the ability to make tears. Some patients will have an underlying endocrine or immunologic condition, such as hypothyroidism and diabetes mellitus. Other causes for dry eye include congenital malformation of the tear glands, distemper virus, neurologic conditions, and toxic effect of certain antibiotics and anti-inflammatory medications. Dogs that have their prolapsed tear glands (“cherry eyes”) removed instead of surgically replaced, are also at a higher risk for developing dry eye.
Patients with mild to moderate dry eye develop a thick, sticky mucoid discharge which becomes crusty and adherent to their eyelids. The discharge is often yellow or green in color. You may need to clean your pet’s eyes and eyelids several times a day. The whites of the eyes (conjunctiva) often appear reddened and somewhat thickened or swollen. As dry eye is uncomfortable, some patients will squint or hold their eyes shut. In more severe dry eye, the cornea (the front clear dome of the eye) becomes red and /or cloudy as blood vessels invade the cornea and scarring develops.
Dry eye is diagnosed following a thorough eye examination including slit lamp biomicroscopy and several diagnostic procedures, along with patient history and clinical signs. One of the most important tests is a Schirmer Tear Test, which measures tear production in millimeters/minute with a very small strip of filter paper. The ophthalmologist will also use fluorescein and Rose Bengal staining to evaluate the surface health of the cornea and conjunctiva, as well as the quality of the tear film.
Fortunately, a number of treatments are available that can help provide relief. The treatment regimen is tailored to the underlying cause for your pet’s dry eye. Our first priority is to increase the patient’s natural tear production. The mainstay of therapy involves tear stimulating medications such as Cyclosporine (Optimmune) or tacrolimus. Tear production markedly increases in most dogs within 1-2 months, however some patients require several weeks to months of consistent treatment before tear function improves. Another important facet of dry eye therapy is control of bacterial overgrowth (bacterial conjunctivitis). For this reason, antibiotic eye drops or ointment may be prescribed in addition to the tear stimulants. In order to reduce inflammation in the conjunctiva and the cornea, antiinflammatory medications may also be necessary. Until tear production increases, artificial tear preparations (viscous eye drops, gels, ointments) are applied frequently to help keep the eyes moist and comfortable.
Depending on the cause, dry eye may be a temporary problem which will improve with treatment and time. In most dogs however, dry eye is a permanent condition that cannot be cured, only controlled. Your pet will likely require some degree of medication long-term. Your ophthalmologist will work to slowly decrease medications over time to find the lowest maintenance level necessary to control the condition.
There are a subset of patients that do not respond to medical management. For these patients, a parotid duct transposition can be considered. This allows saliva to be directed into the eye for constant moisture. If your pet is a potential candidate your ophthalmologist will discuss this procedure with you in detail. Fortunately, with the development of cyclosporine and tacrolimus, fewer and fewer patients need surgery for dry eye.