Dry Eye- Keratoconjuntivitis Sicca

Keratoconjunctivitis sicca (KCS)

“Dry Eye”

Overview

Keratoconjunctivitis sicca (KCS) or Dry Eye is a condition in dogs where the tear production in one or both eyes is reduced. The tears form a protective film over the surface of the eye so if the tear production is reduced, this film becomes compromised and damage to the eye occurs.

Symptoms

The clear surface to the eye, the cornea, is usually kept well hydrated but in KCS, due to a lack of tears, it dries out and becomes inflamed as a result. Affected animals will have red and swollen conjunctiva, called conjunctivitis and often and thick, yellow-green discharge from the eye. Ulceration of the cornea is common and this may cause the usually transparent cornea to look cloudy and opaque. The animal may blink frequently, called blephrospasm, and hold the eye closed or squint as these are signs of a painful eye.

Causes

The most common cause of KCS is immune mediated. This means that the animal's immune system is attacking and destroying the glands of the eye that produce the tears, the lacrimal glands. This is not the only cause however and there are many other things that may predispose your dog to KCS.

• Drugs: A group of antibiotics called sulphonamides can cause temporary or permanent dry eye. Application of topical anaesthetic to the eye, as is sometimes necessary for a thorough eye examination, can also cause a transient reduction in tear production.
• Removal of the third eyelid: The third eyelid is situated in the inner corner of the eye and moves horizontally across the eye. It may occasionally need to be removed for reasons such as removing a tumour but the eyelid contains glands that contribute to the protective tear film and removal of the gland can lead to dry eye.
• Trauma: If damage occurs to the glands producing the tears or the nerves that supply the glands then tear production can be adversely affected and cause dry eye.
• Systemic diseases: Infectious diseases such as distemper can have ocular signs, dry eye being one of them but distemper is covered in your dog's annual vaccinations so if your pet's vaccinations are fully up to date then this will be very unlikely.                  Hypothyroidism, an underactive thyroid gland, can also have reduced tear secretion and therefore dry eye as one of its symptoms.

Some breeds of dog show a predisposition to developing KCS which is likely due to genetic factors. Predisposed breeds include;

• English Bulldogs
   
• West Highland White Terriers
   
• Cavalier King Charles Spaniels
   
• Lhasa Apso
   
• Shih Tzu

Diagnosis

Clinical signs will arouse the vet's suspicion of KCS and then a diagnosis is made using the Schirmer Tear Test (STT). The STT comprises of two strips of blotting type paper, one for each eye. One end is folded over and hooked over the eyelid. The paper is left in place for one minute to absorb the tears. After that time the tear production is measured via a scale printed on the paper strips. The tears will also have picked up a dye placed at the beginning of the strip to make the reading clearer. A low reading on this test strip confirms KCS.

Treatment

If there is an underlying cause, such as hypothyroidism, then treating this cause is likely to reverse the dry eye. If the dry eye is caused by a drug reaction or is immune mediated then it is not reversible and will require lifelong treatment. There are a number of medications that may help to control the condition depending on your dog's particular set of clinical signs and the exact treatment regime will be decided by your vet.

Lacrostimulants: These are products that will stimulate the tear production. The most effective is Optimmune, an ointment containing cyclosporine. Optimunne is usually applied to the affected eye twice daily initially and may take 6-8 weeks to show results. If the treat production increases and the KCS improved then Optimunne can be applied once or twice daily as maintenance therapy throughout life.

Lacromimetics: These are products that mimic or replace normal tears. Examples of these products are Viscotears, Lubrithal and Lacrilube. They have to be applied to the eyes regularly, usually four times a day. They are helpful in long term control of KCS and can be used in conjunction with Optimmune.

Antibiotics and Anti-inflammatories: These may be needed if the KCS is complicated by secondary infection or if the eye is swollen or painful. These may be given topically, as additional ointments in the eye or orally as tablets or liquid in the food.

Also see our Optimmune article.