By Dr. Cory Mosunic, DVM
Some people experience an itchy or burning feeling in their eyes and not surprisingly a common cause of this is due to a drying of the eye. This condition is commonly known as “dry eye” or keratoconjunctivitis sicca (KCS) when eyes do not produce enough tears to keep the surface of the eye moist. It could also stem from the quality of the tear being poor and evaporating too quickly. Did you know that dogs and cats can get “dry eye” too, but how can you tell?
The surface of the eye is similar to skin. For example, in the winter, when our skin is dry, our skin becomes more sensitive, itchy, and often red and cracked. Similar symptoms happen to the eye. Some of the most typical signs of dry eye disease are redness/bloodshot, squinting, and rubbing of the eyes. Sometimes dogs and cats will also present to their veterinarian for a corneal ulcer (sore on the surface of the eye) that is caused due to lack of moisture on the surface of the eye. However, the one tell-tale sign of KCS is an excessive amount of thick yellow goopy discharge coming from the eyes or accumulating on the eyelids. What? That doesn’t make sense. How could an eye that is dry produce all that discharge? Often due to the yellow and pus like nature of the discharge, a misdiagnosis of infection is made, and antibiotics are prescribed, but the discharge does not improve. So, what is all this discharge and why is it seen with dry eyes? The tears that coat the cornea are actually made of three layers, similar to a sandwich. The bottom layer serves as a base coat, called the mucin layer. This is like a paint primer that then helps the middle layer, the aqueous layer (what we know as the actual watery tears), to adhere to the surface of the eye. The third layer is called the lipid layer. The lipid layer is a top protective coat that covers the watery layer with a fatty gel to prevent the tear from evaporating too quickly. Traditional KCS is when the eye does not make enough of the watery/aqueous tears. Consequently, parts of the eye that make the mucin and lipid layers start to work overtime and try to make more fat and mucous to compensate for the lack of the watery tears. Unfortunately, they just can’t adequately compensate for the loss of the tears, but they sure do try! Sometimes the discharge can become so severe it can cause the eyelid to stick together and remain closed.
So why does this happen? Most often there is an underlying immune mediated component which means that the body inappropriately starts attacking the normal gland that produces the tear as if it were a disease or virus and damages it. Therefore, treatment consists of topical eye medications that have to be administered lifelong to continue to prevent the immune system from destroying the tear gland tissue. One of the most common medications to treat dry eye in dogs is cyclosporine (Optimmune). Interestingly, treatment for dry eye is one of the few treatments that was first patented in dogs and then later developed into a different strength for humans called Restasis.
If you or your veterinarian suspect that your pet has KCS/dry eye, then an ophthalmic examination can be performed followed by a Schirmer Tear Test (STT). This consists of a small test strip being placed just inside the lower eyelid for one minute. The tears wet the strip and a measurement is obtained.
Sometimes treating this disease can be tedious and other underlying factors can be contributing to the cause of the dry eye (i.e., certain medications, other diseases, or neurological conditions). It is important that you continue to stay in touch with your veterinarian to update how the treatment is working. Sometimes, there are other medications that need to be utilized. Prior to the development of Optimmune, surgical intervention was the only option to treat this disease. The surgery is called a PDT (parotid duct transposition) in which a salivary duct from the mouth is rerouted to the eye. Yes! That means that when a dog sees food and starts to drool it comes out of the eye. This surgery is not as commonly performed since the introduction of the use of Optimmune/cyclosporine. There are many factors to consider and discuss with a board-certified ophthalmologist prior to performing this surgery.
Certain breeds are more likely to develop KCS and therefore there is likely a genetic cause of KCS. English Bulldogs, Pugs, Lhasa Apsos, and West Highland White terriers are more predisposed to developing KCS.
Early diagnosis is key as well, as continued follow up examinations. With treatment, most patients have a good prognosis for maintaining comfort and vision. If your pet is not responding to treatment, then a consultation with a board-certified veterinary Ophthalmologist may be recommended.
Dr. Cory Mosunic, DVM
Portland Veterinary Emergency and Specialty Care