Does your dog have sore looking eyes? Towards the end of his life, we noticed our senior dog presenting a thick discharge from the eyes, especially in the morning but we did not know about dry eye syndrome, a common eye condition of dogs.
What is dry eye syndrome?
Technically, the disease is known as Keratoconjunctivitis Sicca (KCS). It is the result of inadequate tear production. It is a life-long and progressive disease. Left untreated, it causes constant discomfort and progressive damage to the surface of the eyes. It occurs in approximately one out of 100 dogs.
What are the consequences of dry eye syndrome?
Tears have multiple important functions to protect the surface of the eyes. The tears provide lubrication, nutrition, growth factors, antibacterial defence mechanisms, and provide a physical cleansing action.
What are the consequences of dry eye syndrome?
Tears have multiple important functions to protect the surface of the eyes. The tears provide lubrication, nutrition, growth factors, antibacterial defence mechanisms, and provide a physical cleansing action.
Inadequate tear production results in inflammation and damage to the surface of the eye. Initially, the surface of the eye becomes dehydrated, roughened, and thin. Increased friction, caused by blinking over a dry eye, causes scratching and ulceration of the surface. This can expose nerve endings, causing substantial pain.
Over time, constant inflammation of the surface of the eye causes permanent changes that affect vision: thickening, blood vessel ingrowth, fat and calcium deposition, pigmentation, and scarring across the field of vision. Untreated dry eye syndrome causes constant pain and can progress to complete and irreversible vision loss.
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| Bessie suffered from a severe case of dry eye left untreated (see lead image) and had to have her eyes removed (this image) |
How do we diagnose dry eye?
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| Schirmer's Tear Test |
A length of filter paper is placed on the eye, with one end sitting inside the lower eyelid and the remaining strip sticking out.
This is left in place for one minute. After one minute, we measure how far the tears have travelled down the paper. In a normal dog’s eye, the tears should have travelled 15 mm or more.
A result less than this indicates inadequate tear production. The lower the result, the more severe the disease. Tear production less than 5 mm/min indicates severe disease.
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| Fluorescein stain shows mild damage to the surface of the eyes |
Inadequate tear production can lead to damage to the surface of the eye.
Fluorescein stain is used to assess this. Fluorescein stain sticks to areas of the eye surface that are damaged.
What causes inadequate tear production?
Dry eye syndrome is generally considered an immune-mediated or autoimmune disease. This means that the dog’s immune system starts attacking itself, destroying the structures involved in tear production. The disease is generally considered idiopathic, meaning we do not know why the body suddenly starts doing this.
Sometimes, the dry eye syndrome is part of a wider immune system disorder and may be combined with other immune-mediated diseases, such as systemic lupus erythematosus, pemphigus foliaceus, rheumatoid arthritis, hypothyroidism, diabetes mellitus, polymyositis, atopy, glomerulonephritis, or ulcerative colitis. But, more often, dry eye syndrome occurs by itself.
There are other less common causes of dry eye. These include:
✔️ Drug-induced: Certain drugs, like sulpha-derived antibiotics, can be toxic to the tear-producing structures, and can cause a temporary or, very rarely, permanent reduction in tear production.
✔️ Surgery: The gland of the third eyelid is responsible for 30% of tear production. Damage to or removal of the third eyelid gland can cause dry eye.
✔️ Infectious: Canine Distemper Virus and Leishmania may cause permanent damage to the tear structures, as may any long-term ongoing viral or bacterial eye infection.
✔️ Eye trauma: Trauma to the eye orbit may damage the nerves involved in tear production.
✔️ Neurogenic: Dry eye may occur with dysfunction of the facial nerve.
✔️ Congenital: Rarely, puppies of miniature breeds, such as Pugs, Chihuahuas, and Yorkshire Terriers, may be born without working tear structures.
Are certain breeds more prone?
Certain breeds are more prone to dry eye syndrome: Cavalier King Charles Spaniels, English Bulldogs, Lhasa Apsos, Shih Tzus, West Highland White Terriers, Pugs, Bloodhounds, American Cocker Spaniels, English Cocker Spaniels, English Springer Spaniels, Pekingese, Boston terriers, Miniature Schnauzers, and Samoyeds.
At what age does dry eye syndrome occur?
Dry eye syndrome can begin in the first years of life, particularly in those breeds predisposed, but it can occur at any age. The incidence of dry eye syndrome generally increases with age, as more dogs spontaneously develop the disease over time.
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| Yoda, a male Maltese Terrier displays a thick discharge |
For instance, dogs with bulging eyes (brachycephalic i.e. squashed up face breeds) may suffer sooner or more severely because they also suffer from excess loss of tears due to increased evaporation of tears from the surface of the eye.
A dry environment with heavy heating or air conditioning can do the same. Dehydration can also lead to decreased tear production, causing the onset or worsening of symptoms. Tear production also naturally decreases with age, especially after 10 years of age, as the tear structures deteriorate with aging.
Thus, a larger number of older dogs show dry eye symptoms or suffer more severely.
What are the symptoms?
Dry eye syndrome can affect one or both eyes, but it frequently affects both. Tear production can gradually decrease over time, leading to a gradual worsening of symptoms. Tear production can also wax and wane early in the disease process, resulting in fluctuating test results over time. Thus, early mild dry eye syndrome may be missed.
Initial symptoms of mild disease may include excessive blinking or squinting, increased redness to the whites of the eyes, and a slight mucky discharge.
What are the symptoms?
Dry eye syndrome can affect one or both eyes, but it frequently affects both. Tear production can gradually decrease over time, leading to a gradual worsening of symptoms. Tear production can also wax and wane early in the disease process, resulting in fluctuating test results over time. Thus, early mild dry eye syndrome may be missed.
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| Cavalier King Charles Zigy with a slight mucky discharge |
The surface of the eye may also appear less bright or dull, but not always. In these early stages, it is easy to misdiagnose the disease as a common conjunctivitis and the dog may be put on antibiotic and/or cortisone eye drops.
The drops may temporarily improve the symptoms due to lubrication, but it is temporary, and the symptoms return once the drops are stopped. As the disease becomes more chronic, symptoms become more severe and are not improved much unless appropriate treatment is initiated.
Early symptoms of dry eye include:
✔️ Pain and squinting
✔️ Dry or dull appearance to the eye surface (but not always)
✔️ Mild mucous discharge
✔️ More prominent blood vessels and redness across the whites of the eyes
✔️ More prominent, reddened conjunctiva (the pink areas under the eyelids)
As the disease progresses, constant inflammation of the surface of the eye causes further changes and damage. Later symptoms, with prolonged untreated disease include:
✔️ A thick, ropy discharge that clings to the eye
✔️ Dried up discharge on the eyelids, causing the eyelashes to stick together
✔️ A white haze across the surface of the eye
✔️ Fine blood vessels growing across the surface of the eye
✔️ Dark pigmentation across the surface of the eye
✔️ Grey scar formation over the eye surface
An ulcer (a divot or deficit) may develop on the surface of the eye at any stage in dogs with dry eye syndrome. Eye ulcers are painful. An ulcer can cause a sudden increase in squinting or holding the eye closed, as well as rubbing the eye with the paw or on the ground.
Early symptoms of dry eye include:
✔️ Pain and squinting
✔️ Dry or dull appearance to the eye surface (but not always)
✔️ Mild mucous discharge
✔️ More prominent blood vessels and redness across the whites of the eyes
✔️ More prominent, reddened conjunctiva (the pink areas under the eyelids)
As the disease progresses, constant inflammation of the surface of the eye causes further changes and damage. Later symptoms, with prolonged untreated disease include:
✔️ A thick, ropy discharge that clings to the eye
✔️ Dried up discharge on the eyelids, causing the eyelashes to stick together
✔️ A white haze across the surface of the eye
✔️ Fine blood vessels growing across the surface of the eye
✔️ Dark pigmentation across the surface of the eye
✔️ Grey scar formation over the eye surface
An ulcer (a divot or deficit) may develop on the surface of the eye at any stage in dogs with dry eye syndrome. Eye ulcers are painful. An ulcer can cause a sudden increase in squinting or holding the eye closed, as well as rubbing the eye with the paw or on the ground.
Deep ulcers can potentially cause the eyeball to rupture, leading to permanent blindness. A sudden increase in squinting requires prompt veterinary investigation.
What is the treatment?
Dry eye syndrome is usually treated with specific life-long eye medication. Used fastidiously, such medication is generally quite effective at increasing tear production and reducing symptoms.
What is the treatment?
Dry eye syndrome is usually treated with specific life-long eye medication. Used fastidiously, such medication is generally quite effective at increasing tear production and reducing symptoms.
- Cyclosporine eye ointment is one of the most common treatments used. Cyclosporine is an immunosuppressant and works by reducing the body’s attack on the tear structures, allowing them to regenerate. It also directly stimulates tear production and reduces pigmentation and blood vessel growth over the surface of the eye.
- Tacrolimus is another eye medication that may be used. It works similarly to cyclosporine and is preferred by some ophthalmologists because it is more potent. However, it is more expensive, harder to source, and must be handled with care by owners due to potential toxicity. If cyclosporine does not work, tacrolimus may be tried.
Before applying any eye medication, the eye should be cleaned of any muck using a moist cotton ball. Cyclosporine or tacrolimus eye medication is applied two times per day. It can take up to six weeks for tear production to return to normal.
If there is also a bacterial infection or an ulcer on the eye, antibiotic eye medication will be needed as well. Once tear production has returned to normal, the artificial tears can be stopped. Some dogs may be able to get by on cyclosporine drops given only once per day.
However, most dogs need to stay on twice daily eye medication for life.
Where the specific eye medications are ineffective, surgery may be performed on a salivary gland duct to direct saliva to lubricate the eye. Surgical correction is rare as most cases are effectively managed by eye medications alone.
What is the prognosis?
Untreated dry eye syndrome often progresses to scarring, pigmentation, and blood vessel ingrowth across the surface of the eye, leading to complete vision loss. Most patients respond well to cyclosporine or tacrolimus eye medications, but they need to be continued life-long.
What is the prognosis?
Untreated dry eye syndrome often progresses to scarring, pigmentation, and blood vessel ingrowth across the surface of the eye, leading to complete vision loss. Most patients respond well to cyclosporine or tacrolimus eye medications, but they need to be continued life-long.
Stopping the medication causes the tears to dry up again and symptoms to return. Some dogs, especially those with virtually no remaining tear production (a Schirmer Tear Test result less than 2 mm per minute), may not respond well or at all to the medication. Some types of damage to the surface of the eye are irreversible.
Cyclosporine may reduce surface pigmentation that has occurred by about eighty percent. However, where there is significant damage to the surface of the eye, some scarring, pigmentation, and blood vessel ingrowth will likely always remain. Early treatment offers the best chance for preventing vision impairment.
Zigy's case - early dry eye
Zigy is a young Cavalier King Charles Spaniel.
Recently, he started squinting slightly in both eyes. Sometimes, he had a little bit of mucus sitting on the surface of his eye or on his lower eyelids.
A test to check his tear production showed it to be too low.
Fluorescein dye also showed the surface of his eyes, the corneas, were not healthy.
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| Zigy - Schirmer's Tear Test (left) and Fluorescein dye (right) |
We placed Zigy on cyclosporine eye drops. After a few weeks of treatment his tear production improved to normal levels and his eyes were feeling much better.
Zigy has dry eye syndrome, which is a lifelong condition. He will need to stay on his special eye medication for life.
Written by Dr Meredith Crowhurst, June 2021 for Australian Dog Lover (all rights reserved).
About Dr. Meredith Crowhurst
Dr Meredith Crowhurst is a Melbourne-based locum veterinarian. A Melbourne University graduate with more than a decade of experience, she has extensive consultation and surgical experience and has worked with dogs, cats, rabbits, guinea pigs, rats, mice, birds, and various other animals.
Meredith understands the importance of the human-animal bond. Her aim is to treat pets and their owners with empathy and compassion, delivering the best standard of care.
Previously, Meredith completed a Bachelor of Arts/Bachelor of Science degree and completed her PhD in the biomedical sciences. As well as treating animals, Meredith’s aim is to educate and make medical science knowledge accessible for all.
You can contact her at Tarneit Mobile Vet and follow her on Instagram at instagram.com/
Meredith understands the importance of the human-animal bond. Her aim is to treat pets and their owners with empathy and compassion, delivering the best standard of care.
Previously, Meredith completed a Bachelor of Arts/Bachelor of Science degree and completed her PhD in the biomedical sciences. As well as treating animals, Meredith’s aim is to educate and make medical science knowledge accessible for all.
You can contact her at Tarneit Mobile Vet and follow her on Instagram at instagram.com/
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