Dry Eye In Dogs: Keratoconjunctivitis Sicca (KCS)

Dry eye in dogs, or Keratoconjunctivitis Sicca (KCS), is a common problem that can cause significant ocular discomfort in your dog. In this article, we will explore the many causes of dry eye in dogs and the associated treatment options. In most cases, the prognosis is very good. If you suspect that your dog may have dry eye, please consult with your veterinarian as soon as possible.

What is the lacrimal system and tear producing glands in dogs?

The lacrimal system is responsible for producing tears and keeping the eyes moist. Tears are composed of three layers that together form the tear film: an inner mucous layer, a middle water layer, and an outer lipid (or fat) layer. Tears produced by the lacrimal system play an important role in keeping the ocular surface healthy. Tears supply the metabolic requirements of the cornea, which being avascular has no blood vessels. Without tears, the cornea would eventually lack substance, dry, and potentially become infected or even damaged.

What causes dry eye in dogs (Keratoconjunctivitis Sicca (KCS))?

KCS has multiple possible causes. Several breeds have a higher incidence of keratoconjunctivitis than others, suggesting a genetic predisposition, particularly for the immune-mediated form of the disease. The top breeds predisposed to KCS include the American cocker spaniel, English bulldog, Lhasa apso, Shih Tzu, West Highland white terrier, Cavalier King Charles spaniel, miniature schnauzer, pug, Pekingese, and Yorkshire terrier.

1. Immune-mediated disease - this is the most common cause of dry eye, or KCS, in dogs. This occurs when the body's immune system attacks the tear glands, leading to decreased tear production.
2. Endocrine disease - diseases such as hypothyroidism, diabetes, and Cushing’s disease can all contribute to decreased tear production in dogs.
3. Neurogenic KCS - Any disorder that compromises the function of either the facial nerve (CN VII) or the trigeminal nerve (CN V) can result in decreased tear production in dogs. Loss of nerve function to the glands can be secondary to an inner ear infection, leading to decreased or halted tear secretion.
4. Certain medications - topical atropine, trimethoprim-sulfadiazine (TMS) antibiotic, and sulfonamides can temporarily decrease tear production.
5. Iatrogenic KCS - removal of the third eyelid (nictitans gland) can result in permanent loss of tear production due to its role in tear production.

What are the clinical symptoms of dry eye in dogs?

Keratoconjunctivitis sicca (KCS) is characterized by copious quantities of thick, ropey, ocular discharge. In addition, the most common clinical signs of dry eye in dogs include:

• Blepharospasm (squinting)
• Red-eye, especially of the conjunctival tissues
• Ocular discharge
• Blink excessively due to irritation and discomfort

Corneal pigmentation and scarring commonly occur in chronic cases. When the clarity of the cornea is diminished, vision is impacted. KCS can lead to blindness if it isn’t treated properly.

How is dry eye in dogs diagnosed with the Schirmer tear test?

Dry eye is diagnosed by your veterinarian with a combination of a detailed ophthalmic examination and tests. The most common clinical test used to diagnose dry eye is the Schirmer tear test (STT). This test involves placing a very small strip of paper between the dog's eyelid and eye to measure tear production.

In this test, a strip of filter paper is placed under the lower eyelid and the amount of tears that wet the paper over a given period of time is measured. A Schirmer tear test result of less than 10 mm in 1 minute is considered diagnostic of dry eye in dogs (normal values are >15mm/min).

How is dry eye treated in dogs to increase tear production?

Fortunately, dry eye can be treated quite effectively with a variety of medications and therapies. The goal of treatment is to increase tear production and keep the eyes healthy and comfortable. The following treatment options have been successful in the management of dry eye in dogs:

1. Cyclosporine or tacrolimus - The use of topical immunosuppressive medicines to prevent autoimmune destruction of the glands that produce tears is an effective treatment for KCS. These medications are used to stimulate tear production and prevent autoimmune destruction of the glands. Optimmune® is a veterinary product that is approved for use in dogs with KCS.
2. Pilocarpine - This medication may be administered topically, or orally and is frequently prescribed for neurogenic KCS.
3. Tear replacement therapy - Artificial lubricants are essential and designed to meet the individual needs of your pet. Determining which product is best for you depends on the severity of your dog’s condition, and how it responds. Lubricant use ranges from every 4-6 hrs with most products, many medications can be purchased over-the-counter as well, each differing in composition or price depending on their viscosity level - more viscous preparations are suitable for overnight use because they stay on longer than thinner ones.

In severe cases where medical treatments fail, a surgical procedure called parotid duct transposition may be considered. This involves relocating the parotid salivary gland duct to provide moisture to the eye using saliva.

Breeds prone to KCS

Certain breeds are more prone to developing Keratoconjunctivitis Sicca (KCS) due to their genetic predisposition. These breeds include:

• American Cocker Spaniel
• Bloodhound
• Boston Terrier
• Cavalier King Charles Spaniel
• English Bulldog
• English Springer Spaniel
• Lhasa Apso
• Miniature Schnauzer
• Pekingese
• Pug
• Samoyed
• Shih Tzu
• West Highland White Terrier
• Yorkshire Terrier

These breeds are more likely to develop KCS due to their anatomy, immune system, and genetic factors. For instance, the West Highland White Terrier is particularly susceptible because the body’s immune system attacks the tear-producing glands, leading to decreased tear production. However, it’s important to note that any dog can develop KCS, regardless of breed.

Complications and secondary infections

If left untreated or poorly managed, KCS can lead to several complications and secondary infections, including:

• Corneal ulcers: These are open sores on the surface of the cornea that can be painful and potentially lead to vision loss.
• Chronic conjunctivitis: This is a persistent inflammation of the conjunctiva, which can cause redness, discharge, and discomfort.
• Keratitis: This is an inflammation of the cornea that can cause pain, redness, and vision loss.
• Secondary bacterial infections: These can occur when the eye’s natural defense mechanisms are compromised, leading to infections that can be difficult to treat.
• Vision loss: If KCS is left untreated or poorly managed, it can lead to permanent vision loss.

Working with your veterinarian

As dry eye is a condition that cannot be cured, only managed, it is important that you work closely with your veterinarian and here are some tips:

• Schedule regular check-ups: Regular check-ups with a veterinarian will help monitor the dog’s tear production and adjust treatment as needed.
• Follow treatment plans: Please follow the treatment plan recommended by the veterinarian, including administering medication and using eye drops as directed.
• Monitor clinical signs: You should monitor your dog’s clinical signs, such as redness, discharge, and squinting, and report any changes to your veterinarian.
• Ask questions: You should ask questions and seek clarification on any concerns they have about your dog’s treatment plan.
• Consider a veterinary ophthalmologist: If the dog’s KCS is severe or not responding to treatment, consider consulting a veterinary ophthalmologist for specialized care.

What is the prognosis for dry eye in dogs?

The prognosis for dry eye in dogs is very good when the condition is diagnosed and treated early.

Unfortunately, if left untreated, dry eye can lead to blindness. With appropriate treatment, most dogs will have a good quality of life. Typically, the disease requires lifelong therapy, although the number and frequency of medications can be reduced as it improves.

To keep the disease in good control, frequent recheck visits with your veterinarian are necessary on a permanent basis.

In conclusion, dry eye, or KCS, is a somewhat common condition that can cause significant discomfort and potential vision loss in dogs. Key factors include immune-mediated attacks on tear-producing glands, certain breeds' predisposition, and complications from inadequate tears leading to secondary infections. Early diagnosis and effective treatments, such as immunosuppressive medications and artificial tears, often provide acceptable management of this condition.