Medically known as keratoconjunctivitis sicca (KCS), dry eye syndrome (DES) is a condition characterised by insufficient watery tears reaching the surface of the eye which leads to dryness of the cornea and the conjunctiva. As a result, they become irritated and inflamed due to the lack of lubrication and moisture.
Left untreated corneal ulcers and/or permanent scarring can develop as well as secondary bacterial infection and impaired vision.
The eyes of cats (and all mammals) are kept moist, nourished, and protected by the tears which lubricate the eye and washes away foreign particles. Every time the cat blinks, a thin film of tears are swept over the surface of the eye. Tears are composed of three layers. The outer, oily layer, followed by the watery portion and finally the inner mucus layer.
- The oil (lipid) layer seals the tear, preventing the water component from evaporating. This oily layer comes from the meibomian glands which line the eyelids.
- The water (aqueous) layer lubricates the eye and washes away foreign particles. The lacrimal glands are responsible for the production of the aqueous layer.
- The mucoid layer provides the cornea with nourishment and helps the watery layer spread over and stick to the cornea. This is produced by glands in the conjunctiva.
Dry eye is less common in cats than it is in dogs, it is believed cats are better able to tolerate a reduced amount of tear production.
What are the causes of dry eye?
Herpesvirus is the most common cause of dry eye in cats. This is a common viral infection which produces similar symptoms to that of a cold in humans. Not all cats who contract the herpes virus will go on to develop dry eye.
Other causes of dry eye include:
- Immune-mediated inflammation and/or destruction of the tear glands, the cause of this is not known. Certain breeds of dog are predisposed but I have seen no mention of any genetic predisposition in cats.
- Inflammation of the eyelid (blepharitis) which can cause inflammation and disrupt normal tear production.
- Certain drugs such as general anesthetic, sulfa antibiotics, and atropine.
- Damage to the facial nerve which activates the tear glands, most commonly due to a middle ear infection.
- Removal of the nictitating membrane (third eye) to treat cherry eye.
- Congenital dry eye can occur in Burmese cats due to prolapsed glands.
What are the symptoms of dry eye?
Depending on the cause, either one (unilateral) or both (bilateral) eyes can be affected. Cats with herpes commonly display other symptoms such as sneezing and nasal discharge.
- Excessive blinking.
- Thick, stringy mucoid discharge particularly around the rim of the eyes.
- Painful red eyes.
- Reluctance to open the eyes.
- Swollen eyelids.
- Dry, dull and opaque appearance to the cornea.
- Sensitivity to light (photophobia).
How is dry eye diagnosed?
The symptoms of dry eye can closely resemble those of conjunctivitis and it is not unheard of that a cat is treated for conjunctivitis with no improvement in symptoms. A thorough ophthalmic examination will be performed to determine what has caused dry eye.
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you including any medications your cat is on and any underlying medical conditions and/or recent illnesses or accidents.
Diagnosis is confirmed by a Schirmer's tear test (STT), which involves placing a commercial filter strip under the lower eyelid for 60 seconds. The moisture from the eye will slowly descend down the strip and the level of moisture measured in mm.
In addition, your veterinarian may want to check the eyes for corneal ulcers by placing fluorescein stain into the eyes to check for signs of corneal erosion.
A sample of tears may be taken for culture to determine if your cat has a bacterial infection.
How is dry eye treated?
The goal of treatment is to increase tear production and replace tears as well as addressing the underlying condition where necessary. In some cases, once the underlying problem has been addressed the tear production will return to normal. In many cases, eye drops may be necessary for the rest of your cat's life.
Before applying any of the medications listed below, removal of eye charge with cotton wool dampened with warm water will be necessary. Discard immediately and always wash your hands before and after handling a cat with eye problems.
- Cyclosporine is an immune modulating medication which can suppress immune system inflammation of the tear glands. This product is placed in the eyes twice a day. This medication can be used long term without any residual side effects, however, it may produce stinging in the eye. It can take several weeks for the effects of cyclosporine to take effect.
- Artificial tears will also be prescribed to keep the eye moist and lubricated. These are placed in the eyes three to four times a day. These are the same products people use and are available over the counter from all pharmacies.
- In addition, topical antibiotics may be prescribed to treat secondary bacterial infection.
- Topical corticosteroids may be necessary to treat eye inflammation.
- In cases which don't respond to treatment, parotid (salivary) duct transposition surgery may be recommended. This involves moving the parotid duct which is located in on either side of the cheeks up towards the eyes so they can act as additional tear ducts. Saliva and tears are very similar in composition. This surgery is performed more often on dogs than cats. This surgery is usually carried out by a veterinary specialist. While this surgery is usually successful, eye drops may still be required.
Administer all medications as prescribed by your veterinarian.
Follow-up appointments with your veterinarian will be necessary to monitor your cat's progress.
In many cases, symptoms will drastically improve once your cat begins treatment. However dry eye is usually not curable, and lifelong treatment will be necessary to manage symptoms.