Keratoconjunctivitis sicca (Dry Eye)
What is Dry Eye (KCS) and what causes it?
Traditionally, tears were thought of as a salt-water solution used to lubricate the eye. How wrong we were! It is now known that tears are a complex broth that contains many components, each with a clear and important role in maintaining corneal health and preventing bacterial and fungal colonisation of the eye. In broad terms, the tear film can be broken down in to a lipid component, an aqueous component, and a mucin component. The lipid component is made by the glands in the eyelid (the “Meibomian glands”), and their role is to slow down the rate of tear evaporation. The aquous component is the water of the eye, and it is enerated by tear glands (or “lacrimal glands”). This provides the main lubricating role of the tear film, and constantly flushes off microorganisms from the corneal surface. The final broad component is mucins, which are thick viscous parts that help to anchor the tear film on to the eye (otherwise they would run off like water down a windscreen!).
Therefore, dry eye is a condition that can broadly be divided in to two categories, that of a quantity problem (ie not enough aqueous portion of tears are produced), or a qualitative problem (the tears are being generated, but the quality of the tears are poor from insufficient lipid or mucins). This disease also affects humans.
Dry eye can be caused by trauma, allergies, drug reactions, systemic diseases and neurological disorders . The vast majority of quantitative cases are caused by the body’s own immune system (auto-immune disease). Some breeds of dog seem to be especially predisposed to the disease such as Bull Terriers, Cocker Spaniels, English Bull dogs, Cavalier King Charles Spaniels, Lhasa Apsos, Shih Tzus and West Highland White Terriers. The most common cause of qualitative dry eye issues is chronic allergies and poor blinking.
Clinical signs of KCS
The clinical signs of quantitative dry eye include squinting, copious amounts of thick discharge from one or both eyes, redness, cloudiness in the eyes, and loss of vision. Long term the eyes can go a black colour.
The clinical signs of qualitative dry eye include excessive tear staining, squinting, redness and loss of vision.
Diagnostics
Quantitative dry eye can be easily diagnosed by using a calibrated piece of paper to assess the amount of tears that are generated over a minute (known as the Schirmer Tear Test), when if the clinical signs are fitting, is a very useful and easy diagnostic test. Qualitative dry eye can be diagnosed with a sophisticated piece of machinery that uses many functions to assess the constituents of the tear film. We have an interferometer that allows us to measure the thickness of the tear-film lipid layer, an ultra-HD camera that allows us to measure the amount of tears that can sit within the eyelid, an infrared meibographer that allows us to assess the land health of meibomian glands in the eyelids, and a device that allows us to record the amount of stability of the entire tear film unit. We are the only veterinary clinic in Australasia with this capacity, and we are one of only a few in the world with this expertise to diagnose qualitative tear film disorders so precisely.
Treatment
Treatment for quantitative dry eye may be either medical or surgical. Fortunately most animals respond well to medical therapy. This involves eye drops or ointment designed to stimulate the tear gland to produce more tears. Medication for this condition will usually be lifelong. Cyclosporine or Tacrolimus are the drugs that are usually used to achieve this. Cyclosporine or Tacrolimus may come as a drop or ointment. Additionally, we may use other medications to help such as antibiotics, corticosteroids and lubricants. Surgical treatment for dry eye is occasionally needed in cases where there is no response to medication. The surgery involves moving a salivary gland duct from the mouth to the eye. This results in saliva moistening the eye. The surgery is usually successful, but complications can occur. These may include mineral deposits being formed on the cornea, excessive facial wetting, or blockage of the transplanted duct. These may require further surgery.
Treatment for qualitative dry eye can be tailored, depending on what portion of the tear film is absent. This often involves a combination of replacement therapy, and also medications to try and stimulate better tear quality production.
Regardless of quantitative or qualitative dry eye, cleaning the eye with a warm compress to soak away the crusts is also very important in controlling the disease as the discharge promotes bacterial growth. In some breeds where eyelid closure is poor, we may use eye ointments to lubricate the cornea. If your pet requires oral antibiotics for other problems, sulphur based medications should not be used as they can further decrease tear production.