Keratoconjunctivitis sicca (KCS), commonly known as “dry eye,” is a condition caused by insufficient tear production. This prevalent issue in dogs leads to inflammation of the cornea and surrounding tissues. Tears are composed of water, oil, and mucus, and they serve to lubricate the eye’s surface, supply nutrients, and wash away debris. When the watery component of the tear film is deficient, the eye’s health and function can be compromised.
Causes and Clinical Signs of Dry Eye
The most frequent cause of KCS in dogs is an immune-mediated condition where the body’s immune system attacks the tear-producing glands. This is an inherited disorder common in middle-aged and older dogs. Certain breeds show a predisposition to developing dry eye, including:
- American Cocker Spaniels
- English Bulldogs
- West Highland White Terriers
- Lhasa Apsos
- Pugs
Other factors can also lead to this condition. Systemic diseases such as hypothyroidism or diabetes, and infections like the canine distemper virus, are known to contribute to KCS. Specific medications, particularly sulfa-containing antibiotics, can trigger dry eye that may be temporary or permanent. Additionally, the surgical removal of the third eyelid gland (“cherry eye”) can reduce tear production and increase the risk of KCS.
The signs of dry eye can develop gradually and may initially be mistaken for a simple eye infection. One of the most common signs is a thick, sticky discharge from the eye that is often yellow or green. The eyes may appear red and inflamed, and the cornea can lose its shiny appearance, looking dull or cloudy. Affected dogs often show signs of discomfort, such as excessive blinking, squinting, or pawing at their eyes.
The Diagnostic Process
A veterinarian will diagnose KCS based on the dog’s clinical signs and the results of specific ophthalmic tests. The primary diagnostic tool is the Schirmer Tear Test (STT), which measures tear production. This simple test involves placing a special paper strip inside the lower eyelid for 60 seconds, and the amount of wetting is measured in millimeters.
The results of the STT help determine the severity of the condition. A reading of 15mm per minute or more is considered normal for a dog. Values between 11 and 14 mm/min may indicate early KCS, while readings of 6 to 10 mm/min suggest mild to moderate KCS. A result of 5 mm/min or less is indicative of severe dry eye.
Beyond the Schirmer Tear Test, a complete ophthalmic examination is performed. This will likely include a fluorescein stain, a dye that adheres to damaged areas of the cornea. This stain helps identify any corneal ulcers that may have developed due to the lack of protection from the tear film.
Treatment and Management Strategies
Managing KCS is a lifelong commitment focused on two main goals: stimulating the dog’s own tear production and providing artificial lubrication. Medications that modulate the immune system are the primary treatment for the most common form of KCS. These drugs control the immune response that attacks the tear glands, thereby encouraging the natural production of tears.
Cyclosporine and tacrolimus are the two most frequently prescribed medications for this purpose. Available as ophthalmic ointments or solutions, they are applied directly to the eyes, usually once or twice daily. While these medications do not cure the condition, they are effective in managing it for most dogs. It may take several weeks or months of consistent use to see a significant improvement in tear production.
In conjunction with tear-stimulating medications, artificial tear solutions and ointments are used to provide immediate relief. These lubricants help keep the cornea hydrated and comfortable, which is important while waiting for the primary medications to become effective. Depending on the severity of the dryness, these may need to be applied multiple times throughout the day.
Proper eye hygiene is another component of the management plan. Before applying medication, it is important to gently clean the thick discharge from the dog’s eyes using a warm, damp cloth. This ensures the medication can make direct contact with the eye’s surface and be absorbed effectively.
Long-Term Outlook and Potential Complications
KCS is a chronic condition that, in most cases, cannot be cured but can be successfully managed with consistent, lifelong care. With diligent treatment, most dogs can maintain comfortable eyes and good vision. The prognosis is positive, especially when the condition is diagnosed and treated early before significant damage occurs.
The response to treatment can vary, and regular follow-up appointments with a veterinarian are necessary to monitor tear production and adjust the treatment plan as needed. For some dogs with extremely low initial tear production, medical management may be less effective. In rare cases that do not respond to medication, a surgical procedure called a parotid duct transposition may be considered to redirect a salivary duct to the eye for lubrication.
Failing to treat KCS can lead to serious and painful consequences. Chronic dryness causes persistent irritation and can result in non-healing corneal ulcers, which are susceptible to infection. Over time, the cornea may develop scarring and dark pigmentation, which can impair vision. If left unmanaged, the progressive damage can lead to permanent blindness.