What is keratoconjunctivitis sicca?
Keratoconjunctivitis sicca (KCS) is also commonly referred to as dry eye. The medical term means inflammation of the cornea and surrounding tissues from drying. It is a common eye condition resulting from inadequate production of tears by the lacrimal gland and/or gland of the third eyelid.
What causes dry eye?
Tears are required to lubricate the surface of the eye (cornea and conjunctiva) and remove any debris or infectious agents that may contact the eye. The tear film is a mixture of mucus, fatty liquid, and water.
Any condition that impairs the ability to produce adequate amounts of tear film can result in dry eye. Some of the common causes of KCS include:
- Immune-mediated diseases that damage the tear-producing glands. The body's immune system attacks the cells that produce a portion of the tear film, resulting in decreased production. This is thought to be an inherited disorder.
- Infections such as feline herpes virus.
- Certain medications, such as sulfa drugs (a class of antibiotics).
- Damage to the nerves stimulating the tear glands (neurogenic KCS) by an inner ear infection, trauma, or other condition.
What are the clinical signs of dry eye?
Most cats with KCS have painful, red, and irritated eyes. They may squint, blink excessively, or hold their eyes shut. The eyes have a dull, lusterless appearance due to corneal drying. There is often a thick, yellowish, mucoid discharge present because of the decrease in the watery component of the tear film. Corneal ulceration can also be present.
In chronic cases, there may be a history of eye injury, ulcers, or conjunctivitis. These cats may develop corneal scarring called hyperpigmentation that can be seen on close observation. Corneal scarring often looks like a dark brown film covering the eyes. You may be able to see tiny blood vessels coursing across the cornea (neovascularization). Vision may be reduced if scarring is extensive. One or both eyes may be affected.
How is KCS diagnosed?
Diagnosis is based on medical history, clinical signs, and decreased tear production tests. The most common tear production test is the Schirmer tear test (STT). This simple test uses a special wicking paper to measure the amount of tear film produced in one minute. Additional diagnostic tests may include corneal staining to check for corneal ulcers, intraocular pressure (IOP) to determine if glaucoma is present, and tear duct examination or flushing to ensure normal tear drainage.
How is dry eye treated?
The treatment of dry eye has two objectives: to stimulate tear production and to replace tear film, thereby protecting the cornea. There are two commonly used eye medications to stimulate tear production: cyclosporine (brand name Optimmune®) and tacrolimus. Both are easily placed in the eyes once or twice daily. These drugs are very safe, and most cats improve dramatically with their consistent use. Pilocarpine (brand name Isopto-Carpine®) is a medication used in the treatment of neurogenic KCS.
Tear film replacement is often used in combination with a tear production stimulant. This is critical to keep the cornea moist and healthy, especially during the initial phase of treatment. Most cats will receive tear replacement every two to six hours, depending on their need and severity of condition. Some cats will require antibiotics or anti-inflammatory eye medications to treat secondary infection and inflammation.
Gently cleaning the eyes several times per day with a warm, wet washcloth will help your cat feel better and may help stimulate tear film production. Your veterinarian will demonstrate the correct way to administer your cat's eye medication and address any questions you may have about caring for her.
What if I can't apply the medication?
If you are unable to administer your cat's eye medication, surgery may be an option. Surgical correction involves repositioning the salivary duct so that it secretes saliva onto the eyes. This surgery is usually performed by a board-certified veterinary surgeon or ophthalmologist. There is a significant risk for complication so it should not be pursued unless all other treatments have failed.
What is the prognosis for a cat diagnosed with KCS?
With today's tear-stimulating drugs, the prognosis for cats diagnosed with KCS has never been better. Dry eye requires lifelong medical care. With diligent attention and monitoring, many cats can enjoy a pain-free, visual life. If the condition is diagnosed late in the course of the disease and if extensive corneal scarring has developed, the cat may not respond fully or regain its vision. Once corneal scarring has developed, there is little that can be done to reverse it. It is critical that you carefully follow your veterinarian's treatment plan to maximize the likelihood of a successful outcome.