DRY EYE (KERATOCONJUNCTICITIS SICCA)
Dry eye refers to a decrease or lack of watery tear production. The tear film is composed of three layers: an oily layer to prevent evaporation of tears, the aqueous or watery layer, and a mucous layer next to the cornea that allows the tear film to smooth evenly across the cornea. The importance of a healthy and adequate tear film cannot be overstated.
Unlike other organs in the body, the cornea is free of blood vessels. Therefore, the cornea or clear windshield to the eye, relies on the tear film for oxygen and other nutrients. When dry eye occurs, the cornea loses this nutrient supply and becomes desiccated. This leads to corneal ulcers, conjunctivitis, ocular infections, patient discomfort, corneal vascularization, corneal scarring, and corneal mineralization. Humans describe the sensation of dry eye as having sandpaper in their eyes.
It may be counterintuitive, but dry eye actually causes discharge. As the watery or aqueous portion of the tear film decreases, the other 2 layers begin to over secrete in an attempt to account for the deficit. Patients will develop a thick tenacious discharge which can become adherent to their eyelids and become crusty. The discharge is often yellow or green in color. You may find yourself cleaning your pet’s eyes several times a day.
Patients will also have blood shot eyes where the white part of their eyes becomes red.
As dry eye is uncomfortable, some patients will squint or hold their eyes shut.
In more advanced cases, the cornea may become red or cloudy as blood vessels invade the cornea.
CAUSES OF DRY EYE
The most common cause of dry eye in our companion animals is an auto-immune attack on the tear gland. The immune system is overactive and destroys the tear producing gland above the eye.
Other causes for dry eye include being born without a tear gland, hypothyroidism, diabetes mellitus, distemper virus, neurologic conditions, as well as a toxic effect of certain antibiotics and anti-inflammatory medications.
TREATMENT OF DRY EYE
The treatment of dry eye is multi-factorial. As there are different causes for dry eye, there are different treatment regimens.
Our first priority is to increase the patient’s natural tear production. Luckily, we have topical medications that have been shown to markedly increase tear production over the course of 1 to 2 months. These medications include Optimmune® (cyclosporine) and Tacrolimus. The veterinary industry has been treating dry eye with cyclosporine since the 1980’s. Recently, Restasis® was introduced to the human market for the treatment of dry eye in people. Just one way that veterinary medicine has contributed to the human medical field!
Frequently, patients with dry eye have an overgrowth of bacteria around the eye. For this reason, antibacterial medications may be prescribed in addition to the tear stimulants.
In order to reduce inflammation in the conjunctiva (white part of the eye) and the cornea, antiinflammatory medications may also be necessary.
Artificial tear preparations will help keep the eyes moist until natural tear production increases to a normal level. These come as drops, gels, and ointments. Your veterinary ophthalmologist will recommend the most appropriate preparation for your pet.
Dry eye is a condition that we can control but typically not cure. Your pet will likely require some degree of medication long-term. Your veterinary ophthalmologist will work to slowly decrease medications over time to find the lowest maintenance level necessary to control the condition.
The medications are designed to halt progression of dry eye and even reverse the damage low tear production has done.
The vast majority of patients respond very well if medications are administered as directed. Your pet is relying on you to control their dry eye condition and make them more comfortable.
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. Your veterinary ophthalmologist can discuss this procedure with you in detail. Happily, with the advent of cyclosporine and tacrolimus, fewer and fewer patients need surgery for dry eye.