What is “dry eye?”
Keratocunjunctivitis Sicca (KCS) or dry eye as it is commonly known, is a condition found in humans and animals where the eyes do not produce enough tears or moisture for the eyeballs to stay moist and shiny.
Which animals are prone to dry eye?
The condition is common in dogs and rare in cats. Cats who do suffer from the condition tend to show fewer symptoms of eye problems than dogs. Certain dog breeds are predisposed which include Cocker Spaniels, Bulldogs, West Highland White Terriers, Lhasa Apsos and Shih Tzus.
What are the symptoms of dry eye?
The symptoms associated with the condition can vary and are not necessarily very specific. This is why the owner of a pet with dry eye will realise there is something wrong with the dog’s eyes, but they cannot exactly describe what it is. The typical symptoms which one may notice vary and may include a combination of redness and swelling up of the inside of the eyelids (called chemosis), redness of the sclera (the white part of the eye next to the front “see through” (cornea) part of the eye), a discharge in the corner of the eyes, eyelids which are half open or sometimes closed tightly (blepharospasm), the third eyelids starting to move over the eyeball from the inside corner of the eye. Humans with this condition will tell you that it feels like there is sand in their eyes. One can imagine that if there is not sufficient moisture or tears to lubricate the eyeballs that the movement of the eyelids over the eyeball becomes strained every time the animal blinks. In bad cases which have been going for a while, the dryness on the eyeball can cause ulcers to start forming on the cornea with tiny blood vessels starting to appear on the shiny “see through” front part of the eyeball, the cornea. In severe cases, dry eye can lead to loss of vision and partial blindness.
Causes of and risk factors for dry eye
There are a wide range of reasons, conditions and external causes which can lead to dry eye.
Immunologic – Diseases, where the immunity of the animal is compromised or excessively challenged in one way or another, can lead to dry eye. One example is Atopic Dermatitis. This is an allergic skin condition often brought on by the inhalation of allergens like pollens (similar to hay fever in humans), which causes overall itching and scratching with areas of the skin being irritated and red and inflamed.
Congenital – A condition an animal is born with, with certain breeds like Pugs and Yorkshire Terriers more commonly affected.
Neurogenic – occasionally seen after trauma to the face like bite wounds or a car accident where the nerves supplying the tear gland or lacrimal gland are damaged.
Drug or procedure induced – Atropine which is a drug sometimes used to expand the iris so a proper eye exam of the back of the eye (the retina) can be performed will sometimes lead to a transient dry eye. In time this should clear up with no medication required. The same thing can happen when an animal is given a general anaesthetic (GA) and the vet forgets to put an ointment in the eye to cover the cornea, whilst they are doing a medical or surgical procedure. Most people do not realise that animals who are under general anaesthesia sleep with their eyes open. If dry eye happens because of a GA, it will usually clear up by itself a few days later.
Drug toxicity – One group of antibiotics called potentiated sulphonamides have been known to
cause transient or permanent dry eye.
Iatrogenic – Iatrogenic refers to an illness which is brought on by human intervention, typically a medical examination or treatment. The most common cause in dogs will be the removal of the third eyelid or membrana nictitans. There is a condition where this third eyelid starts moving over the eye and only in very exceptional circumstances should this third eyelid ever be removed.
Radiotherapy – Cancer of the eyelids is common in animals with white skin or low pigment in their skin. The treatment of this cancer may require radiotherapy where the beam needs to be aimed at the eyelids with the result that the eye itself is being radiated as well and this can lead to dry eye.
Chronic conjunctivitis – An inflammation with redness and swelling of the eyelids. This condition is more common in cats who suffer from chronic herpes or chlamydia infection.
Can dry eye be confused with other conditions of the eye or the eyelids?
Yes indeed. Dry eye can often be confused with bacterial conjunctivitis. The reason for this is that dry eye will often lead to a situation where there is a secondary overgrowth of bacteria because of the compromised situation of the eye and eyelids. The secret to differentiate lies in the diagnosis which is discussed below.
How is dry eye diagnosed?
Dry eye is diagnosed with the Schirmer tear test. The Schirmer tear test is a simple procedure where a small piece of special absorbable paper is bent over on the one side and hooked on to the lower eyelid of the animal. The rate at which the paper gets wet and the moisture moves down on the piece of paper determines whether enough tears are formed to keep the eye wet. Usually, the paper needs to get wet at the rate of 14 mm per minute. If this does not happen and the paper only gets wet too for instance 5 mm within a minute, it confirms a diagnosis of dry eye.
Other diagnostic tests which the vet may want to perform are fluorescein staining where a bright orange fluid is dropped onto the eyeball. If there is an ulcer on the cornea (which often happens with dry eye) the colour will turn a bright green. If an ultraviolet light is shown onto it, it will turn even brighter and “fluoresce”. The vet may want to take a swab of the eye to do a culture and antibiogram in cases where treatment seems to be unsuccessful. The vet may also want to do a cytobrush test where a tiny “roller brush” is rolled onto the inside of the eyelids, smeared onto a microscope slide, and examined under a microscope. The diagnostic tests done will depend on the particular circumstances of each individual animal suspected to be suffering from dry eye.
How is dry eye treated?
Animals with a confirmed diagnosis of dry eye are usually treated as outpatients. The eyes have to be cleaned before the medication is administered. Owners are usually instructed to keep the eyes and the area around the eyes as clean as possible on an ongoing basis. This is usually done with wiping the eyelids with cotton wool or cloth moistened with lukewarm water or a saline solution. If the animal seems to be developing more pain as the treatment goes on, it is important to get such an animal back to the vet as soon as possible because animals with dry eye are predisposed to severe corneal ulceration if not attended to. In previous decades, before more modern and effective medication was available to treat dry eye a surgical procedure was done were the parotid duct, a small duct which transports saliva from the salivary glands to the back of the mouth, was surgically redirected to the corner of the eye. For lack of anything else this procedure did help to some degree but the saliva tended to be irritating to the cornea and some animals were always uncomfortable after surgery. Fortunately, there are great and effective drugs available to treat this condition today and the two most commonly used medications which stimulate the eye to produce tears are Cyclosporin and Tacrolimus. The vet will assist you in choosing the right option for your pet.
Prognosis for dry eye
Depending on the cause of dry eye, the outcome of treatment is usually very positive these days with the drugs available to help stimulate tear production for the eye. If there are no other conditions like ulceration of the eye, complicating the treatment, animals with dry eye can live good quality lives until they die but will most likely require life long treatment and regular veterinary checkups.
If you are not sure if your dog who seems to have an eye problem has dry eye, bring him or her to the vet for a checkup and have the correct diagnosis made and correct treatment recommended.
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