A Dog Owner's Guide to Canine Dry Eye
It’s not often a topic makes a particular patient instantly spring to mind, but say “dry eye” (keratoconjunctivitis sicca) and I immediately think of Ben, a gorgeous bear of a German shepherd.
Ben was a gentle giant, an imposing dog that some children avoided, and yet all he wanted was love. But what truly impressed me about Ben was the he lived with the constant, nagging, burning soreness of severe dry eye – and he never once complained or grumbled.
For those unfamiliar with the condition, dry eye is just what it says. The eye is deficient in the natural moisture supplied by tears, and so the surface lacks lubrication and dries out. This is like having permanently hot itchy eyes, and every time you blink sand rubs into your cornea (the surface of the eye). Now you begin to understand why Ben’s gentle patience was so outstanding.
Perhaps your dog has gloopy eyes, or rubs his face a lot, and now you are wondering if he has dry eye. What are the signs to look for?
Signs of Dry Eye
A healthy eye glistens: The moisturizing tear fluid that bathes the cornea makes it shiny and bright, but a dry eye lacks luster. To check this out, see if you can see reflections in your dog’s eye. Whereas a normal cornea acts like a mini mirror, a dry eye has a dull, matt surface.
Dry eyes are sticky: Nature is clever. Tear fluid is made up of two elements: an aqueous (watery) part and a mucus component. The mucus mixes with the aqueous part to hold it in place, a bit like coating the cornea in cling film. However, even when the aqueous is absent the mucus is still present but in its thick, undiluted form. This means a tacky, gummy discharge which can be so sticky as to glue the eyelids together.
Red eye: The dry eye quickly becomes sore and inflamed, which means the white of the eye looks angry and red.
Pigment patches: The cornea is delicate structure and it doesn’t cope well with the constant sandpaper-like rubbing of eyelids over the dry surface. To protect it, the normally transparent cells of the cornea toughen up and become impregnated with pigment. These look like blotches of (usually) brown pigment on the surface of the eye. Taken to an extreme, these pigment patches can take cover the entire surface and the dog loses his vision.
Blinking and rubbing: Some dogs cope with the constant discomfort by squinting, and keeping the eye partially closed. Others can’t resist the urge to rub at the eyes and scoot their faces along the ground. (Of course, rubbing their face can be a sign of other things such as an ear infection, or dental issues, so don’t jump to conclusions based on this alone.)
There is a pattern that dogs from certain breeds are more at risk than others. Ben was a German shepherd, and indeed dry eye is not uncommon in this breed. Others that seem to suffer from more than their fair share of this condition include Cocker spaniels, West Highland white terriers, Shih Tzus, Cavaliers, Bulldogs, Bull terriers, miniature Schnauzers, Chihuahuas, Pekinese, and Dachshunds.
So if you’re worried your dog has dry eye, where do you go from here?
Diagnosing Dry Eye
Confirming your suspicion and diagnosing dry eye is relatively simple, and something your veterinarian can do in the clinic. However, to avoid interfering with the test results be sure that you don’t wipe the eye or use any sort of eye drop on the day of the appointment.
Schirmer Tear Test
This diagnostic test measures how much tear fluid is (or isn’t!) produced, and is simplicity itself. The Schirmer test strips are narrow lengths of filter paper marked up in millimeters, like a miniature paper ruler. The clinician folds the end of the test strip to form a hook, which she sits in the pocket formed between the lower eyelid and the cornea. [£] [$]
The idea is the strip wicks moisture, which travels down the paper. The vet times one minute, at which point she removes the strip and records how far the moisture traveled.
- 15 – 25 mm travelled in 1 minute is considered normal
- 10 – 15 mm is OK
- Less than 10 mm points towards inadequate tear production
- Less than 5 mm confirms dry eye.
Both eyes are tested, because this condition may affect one eye or both or indeed one eye may be worse than the other. If the results are in a gray zone it’s best to repeat the test a week or so later to see if things have got better or worse.
Checking overall eye health
Your vet also looks at the overall health of the cornea, checking for ulcers, inflamed blood vessels, and pigment patches. This is to assess if other factors are aggravating the condition, such as eyelashes rubbing on the surface and in-turned eyelids. Each of these problems then needs addressing in its own right.
Before considering which therapy to use (and some excellent options are available) it helps to know the mechanism behind dry eye because this helps you understand the treatment choices.
The Causes of Dry Eye In Dogs
There are several potential causes, but head and shoulders above the rest is autoimmune disease. Let’s take a quick peak at them all:
- Autoimmune disease: The body attacks its own tear producing glands
- Nerve damage: Infection, inflammation, or cancer damages the nerves which tell the eye to produce tears (Rare)
- Trauma: If the eye prolapses from the socket, this stretches the nerves and interferes with tear production. With treatment, these cases may get better after one or two months
- Drug side effect: Unfortunately, in some dogs certain medications can have the unwanted side effect of inducing dry eye. Most commonly, these are drugs that contain sulphonamides, such as salazopyrin (for colitis) or sulphonamide antibiotics.
A Deeper Look at Autoimmune Disease
By far the commonest cause of dry eye is autoimmune disease. Here, the body’s immune system gets confused, and instead of fending off invading bacteria it picks on the glands that produce tear fluid. Immune cells flood into the glands (as if they were attacking the body) in such numbers they destroy the glands’ structure and they can no longer produce tear fluid.
No one is quite sure why this happens, although exposure to ultraviolet light, such as bright sunshine, worsens the immune attack.
In some cases, if the dog receives treatment early and responds well, the damage may be reversed. However, the majority of dogs need regular medication to control the signs and keep the eye comfortable.
Treatment for Dry Eye
Happily, there are options for treatment, including medical therapy or surgery. However the surgical option is hardly used now, because the eye ointments are so good.
The ideal drug would stop the body attacking the tear glands and leave them to do their job in peace. Happily, this is exactly what the most recent drug therapy option does.
State of the Art Therapy
A drug called cyclosporine was developed on the back of organ transplant medicine. When given by mouth cyclosporine stops transplanted organs being rejected. But with regard to dry eye veterinarians didn’t want to use a sledgehammer to crack a nut and so a topical ointment containing cyclosporine was developed. When this ointment is put into the eye it acts locally to protect those precious tear glands.
You put half an inch of cyclosporine into the eye twice daily. Some dogs respond brilliantly within six weeks of starting therapy, and the good responders can be weaned down to once daily treatment, or sometimes even every other day. This can be a big help to owners because not only is this more convenient, but the ointment is expensive, so less frequent applications help the pocket book.
The downside of cyclosporine is the expense, which puts it outside some owners reach. This was the case with Ben, so we had to explore the next best option of anti-inflammatory drops and artificial tears.
Much of the discomfort comes from inflamed itchy eyes. In a two-pronged attack steroid drops decrease the inflammation, whilst false tears provide lubrication. Steroids are cheap, but can’t be used if the cornea is ulcerated because it makes the ulcer worse. Happily, Ben’s eye was healthy enough to cope with steroids, which his owner put in with great dedication three times a day.
However, steroids are not the end of it because regular application of artificial tears is needed to moisten the eye. Indeed, not all artificial tears are the same, and their formulation governs how long they last in the eye. Some consist of sterile saline, which evaporates pretty quickly and so needs hourly application – quite a big ask for owner and pet.
Other artificial tears are formulated in an oily base, which helps them stick around for longer, or more sophisticated still there are some made with hyaluronic acid which again has superior persistence and the manufacturers claim two to three times application is sufficient in some dogs.
This is mainly reserved for dogs that do not respond to medical treatment or it’s impractical to put drops in regularly. The procedure involves rerouting the duct from the parotid salivary gland, so that instead of saliva draining into the mouth it empties into the eye.
Part of the reason this technique has fallen out of favour is the eye may “water” heavily when the dog sees something tasty to eat, and indeed this can lead to problems where the skin becomes too wet and infection sets in.
Thanks to the dedication of his owners, Ben coped with his dry eye for years; steroids and false tears kept the condition at bay. However, there is no doubt that cyclosporine therapy offers real hope, and along with improvements in artificial tear technology the future looks brighter for dry eye.