Overview

Keratoconjunctivitis sicca (KCS), or dry eye, is a condition in which there is inadequate production of the watery component of tears, causing inflammation on the eye surface. KCS in dogs causes redness, irritation, thick, green discharge and they are at risk of developing painful corneal ulcers. If left untreated, KCS can lead to scarring, blood vessel formation and secondary infections on the cornea, potentially resulting in permanent vision loss. 

Although improvement may take a few weeks, most dogs respond well to treatment. However, KCS usually requires lifelong management. 

Cause

The most common cause of KCS is immune-mediated inflammation of the tear-producing (lacrimal) glands. While KCS can occur at any age, it is most common in middle-aged dogs.

Other potential causes of KCS include:

• Chronic allergies
• Endocrine diseases (e.g., diabetes and hypothyroidism)
• Congenital factors
• Surgical removal of the third eyelid gland (gland of the nictitans membrane)
• Infections (canine distemper virus)
• Certain drug toxicities (e.g., sulfonamides or etodolac)
• Radiation treatment

Less commonly, KCS can result from loss of nerve function to the lacrimal gland or cornea (neurogenic KCS). This may occur from inner ear disease, trauma, tumors, or without an identifiable cause (idiopathic).

Tear film consists of three layers: the mucin layer, the aqueous (watery) layer, and the lipid (oily) layer. KCS affects the aqueous layer due to inflammation in the tear glands, resulting in quantitative dry eye. This differs from qualitative dry eye, which arises from abnormal lipid or mucin levels in the tears and involves other structures of the eye (meibomian glands and conjunctival goblet cells). This article focuses on quantitative dry eye. 

Breed predisposition

KCS can occur in any breed of dog, but is more common in certain breeds, including:

• American Cocker Spaniel
• English Bulldog
• Lhasa Apso
• West Highland White Terrier
• Cavalier King Charles Spaniel
• Shih Tzu
• Pug

Clinical signs

Signs of KCS may include:

• Thick yellow-green eye discharge
• Dull or dry appearance to the eye
• Redness
• Squinting
• Pawing or rubbing at the face
• Blood vessels or dark pigment on the cornea in chronic cases

KCS typically affects both eyes, but in neurogenic KCS, only one eye is often affected, and dryness is often seen on the same side of the nose. 

Diagnosis

KCS is diagnosed with a Schirmer tear test (STT), which measures aqueous tear production in dogs over one minute. Because corneal ulcers can occur secondary to KCS, your veterinarian may also perform a fluorescein stain test, which is a special type of dye that adheres to and highlights any areas of corneal damage.

Treatment

Treatment for KCS may include:

• Medicated eye drops (such as cyclosporine or tacrolimus), which help the eyes produce more tears and reduce inflammation. In neurogenic KCS, a different medication, pilocarpine, may be used for treatment to stimulate tear production.
• Artificial tears to lubricate the eyes.
• Topical antibiotics if secondary infections are present.

In some cases, you may be referred to a veterinary ophthalmologist for treatment. For severe or unresponsive cases, surgery may be recommended—most commonly, a parotid duct transposition. This procedure reroutes the salivary gland duct into the inner pocket of the dog’s eye to provide moisture. Some dogs may still require medication after surgery. 

Outcome

KCS is a chronic condition that generally requires lifelong treatment. Early and consistent management can greatly improve comfort and long-term outcomes. If left untreated, KCS will progress, causing significant discomfort and potentially leading to permanent eye damage or vision loss. 

With appropriate treatment, most dogs will show improvement within a few weeks; however, signs of improvement may take up to twelve weeks in some cases. Dogs with very low or absent tear production at diagnosis tend to have a poorer response to treatment.