Keratoconjunctivitis Sicca
Keratoconjunctivitis sicca
Also known as: KCS, dry eye, xerophthalmia
CatDogUrgency: Low
Keratoconjunctivitis sicca
Also known as: KCS, dry eye, xerophthalmia
In short
Keratoconjunctivitis sicca (KCS), or dry eye, is a common condition in dogs and occasionally cats where inadequate tear production leads to chronic eye irritation, thick discharge, and potential vision loss. Fortunately, lifelong topical therapy successfully manages the disease in most pets.
TL;DR. Keratoconjunctivitis sicca (KCS), commonly known as dry eye, is a painful condition where a pet cannot produce enough tears, leading to chronic eye irritation, thick discharge, and potential vision loss that requires lifelong daily treatment.
Thick, sticky mucoid discharge and a dull corneal surface are classic signs of keratoconjunctivitis sicca (KCS) in dogs.
Keratoconjunctivitis sicca (KCS), widely referred to as "dry eye," is a common and potentially serious ophthalmic disorder in dogs, and less frequently, in cats. The term literally translates to inflammation of the cornea (kerato) and the conjunctiva (conjunctivitis) due to dryness (sicca). To understand KCS, it helps to understand the tear film. The tear film is not just water; it is a complex, three-layered barrier that coats the eye. It consists of an outer oily (lipid) layer that prevents evaporation, a middle watery (aqueous) layer that nourishes and cleanses the cornea, and an inner mucus (mucin) layer that helps the tears stick to the eye's surface.
KCS primarily occurs when there is a deficiency in the middle aqueous layer, though it can also be caused by an increased rate of tear evaporation. As a leading veterinary critical care textbook notes:
"A deficiency in any of these components may result in decreased tear production or increased tear clearance (evaporation) and may be diagnosed with a Schirmer tear test. Clinical signs of a tear film abnormality depend on the severity, chronicity, and underlying cause of the tear deficiency."
Without an adequate watery layer, the eye loses its primary defense mechanism. The constant friction of the eyelids rubbing against a dry corneal surface causes chronic irritation, inflammation, and pain. Over time, this lack of lubrication leads to severe corneal damage, secondary infections, and potentially permanent blindness if left untreated. For pet owners, recognizing the early signs of KCS is vital to preserving their pet's vision and comfort.
The vast majority of KCS cases in dogs are immune-mediated. In these patients, the animal's own immune system mistakenly targets and destroys the lacrimal (tear-producing) glands. A prominent veterinary pharmacology reference explains:
"Keratoconjunctivitis sicca (KCS) is a common ocular disorder in dogs. Recent research efforts indicate that KCS in dogs is an immune mediated disease. It is similar to Sjogren's Syndrome [in humans]."
While immune-mediated destruction is the primary culprit, other causes and risk factors exist:
"A topical lubricating ointment should be applied at least every 4 hours for 24 hours following anesthesia to decrease ocular surface drying, which may lead to corneal ulceration."
The clinical signs of KCS can vary depending on how long the disease has been present and how severely tear production is reduced. Owners should watch for the following symptoms:
A dry, crusty nose on the same side as the dry eye is a classic indicator of neurogenic KCS.
Diagnosing KCS is straightforward and relies on a quick, non-invasive test called the Schirmer Tear Test (STT). This is the gold standard diagnostic tool for dry eye.
During a Schirmer tear test, your vet will place a small, specialized, calibrated paper strip inside the lower eyelid of your pet's eye. The strip is left in place for exactly 60 seconds. As tears are produced, they travel up the paper strip, which is marked in millimeters.
The Schirmer tear test is the gold standard diagnostic tool used to measure tear production.
Because cats have highly variable tear production when stressed, interpreting the STT in felines is more challenging. Your vet will evaluate the STT results in cats alongside clinical signs like conjunctivitis and corneal changes.
In addition to the STT, your vet will perform a fluorescein stain test. This involves placing a temporary green dye into the eye to check for corneal ulcers. Because dry eyes are highly prone to ulceration, and because certain treatments (like topical steroids) can prevent ulcers from healing, ruling out corneal ulcers is a critical step before starting any therapy.
Treating KCS requires a multi-pronged approach aimed at stimulating natural tear production, replacing missing tears, and reducing inflammation. Because the vast majority of cases are immune-mediated, immunosuppressive eye drops are the cornerstone of therapy.
Cyclosporine is an immunosuppressant ophthalmic agent that targets the T-cells responsible for destroying the tear glands. By calming the local immune response, cyclosporine allows the lacrimal glands to recover and produce natural tears. It also has direct anti-inflammatory properties that help clear corneal scarring and pigment over time.
While highly effective in dogs, its use in cats is less common. A leading veterinary drug reference notes:
"Cyclosporine has been tried in the management of the rare case of keratoconjunctivitis sicca in the cat."
It is important to note that human-strength over-the-counter or prescription dry eye drops (such as 0.05% cyclosporine emulsions) are generally too weak to stimulate tear production in dogs. Your vet will prescribe a veterinary-approved ophthalmic ointment or a higher-concentration compounded formulation.
If a dog does not respond adequately to cyclosporine, your vet may prescribe tacrolimus. Tacrolimus is a potent calcineurin inhibitor that works similarly to cyclosporine but is often more effective in stubborn cases. As noted in veterinary pharmacology texts:
"Patients failing to respond to the veterinary approved ophthalmic ointment may respond to compounded cyclosporine 1% ophthalmic solution or tacrolimus 0.03% ophthalmic solution."
Tacrolimus must be prepared by a specialized compounding pharmacy and is applied daily as an eye drop or ointment.
For cases of neurogenic KCS (where the nerve pathway is damaged), immunosuppressants like cyclosporine may not work. Instead, your vet may use pilocarpine, a parasympathomimetic drug. Pilocarpine stimulates the remaining nerve endings to trigger tear and nasal gland secretions. It is typically administered orally in the pet's food, with the dose carefully adjusted by your veterinarian to avoid systemic side effects like vomiting, diarrhea, or excessive drooling.
Until tear-stimulating medications take full effect—which can take up to four to six weeks—frequent application of over-the-counter artificial tear lubricants is essential. These lubricants help keep the cornea moist, protect the eye from friction, and flush out debris and thick mucus.
The prognosis for pets with KCS is generally excellent, provided the owner is committed to lifelong care. The success rate of alleviating clinical signs and restoring comfortable tear production with cyclosporine is approximately 75% to 85% in dogs.
However, owners must understand that KCS is a chronic, progressive disease that cannot be cured, only managed. Discontinuation of therapy usually results in the rapid return of clinical signs within a few days, along with the resumption of immune-mediated damage to the tear glands. If therapy is stopped permanently, the tear glands will eventually suffer irreversible atrophy, leading to permanent blindness and chronic pain.
For cats, because KCS is rare and often secondary to chronic viral infections, long-term prognosis data is limited, and treatment must be tailored carefully to avoid flaring up underlying viral diseases.
Because the primary cause of KCS is an inherited, immune-mediated condition, there are no proven lifestyle changes or preventive measures to stop the disease from developing. However, you can prevent the severe, vision-threatening complications of KCS through:
If your pet has been diagnosed with KCS, or if you suspect they are developing it, you should monitor their eyes daily. You must call your veterinarian immediately if you notice any of the following red flags:
Corneal ulcers in dry eyes can deteriorate rapidly, sometimes causing the eyeball to rupture within 24 to 48 hours if left untreated. Prompt veterinary intervention is vital.
Certain dog breeds are highly suspected of having an inherited predisposition to developing immune-mediated KCS. These include:
If you own a Chinese Crested Dog or a Yorkshire Terrier, it is highly recommended to have a Schirmer tear test performed as part of their routine annual physical examination, even if their eyes appear normal. Early detection allows for treatment to begin before significant, irreversible damage to the tear glands occurs.
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Keratoconjunctivitis sicca (KCS), or dry eye, is a common condition in dogs and occasionally cats where inadequate tear production leads to chronic eye irritation, thick discharge, and potential vision loss. Fortunately, lifelong topical therapy successfully manages the disease in most pets.
thick mucoid discharge、conjunctival hyperemia、lackluster appearance to the corneal surface、corneal ulceration、corneal vascularization、melanosis、thickening of the corneal epithelium、dry, crusty nose ipsilateral to the dry eye
Schirmer tear test
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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