If you have children, or your eyes frequently well up while you are reading books, or watching movies or advertisements, you are probably well aware of tears. Humans are the only species to have emotional tears, and scientists have studied and debated their purpose since 1500 BC. Theories range from tears serving to cleanse stress-generated toxins from the blood, to the more credible explanation that tears foster necessary emotional connections between humans. Tears also serve a more basic biological function by providing nutrients, removing debris and infectious agents, and keeping the eyes moist. However, when biological tear production is disrupted, you or your furry friend could suffer from dry eye (i.e., keratoconjunctivitis sicca).
Dry-eye basics in pets
Tears may appear to be a uniform clear liquid, but actually consist of three portions:
- A fatty (i.e., lipid) component, produced by the meibomian glands that line your pet’s eyelids
- A liquid (i.e., aqueous) portion that comes from the lacrimal and third eyelid glands
- A mucous portion, supplied by conjunctival goblet cells
Pets with dry eye usually produce a low amount of the liquid portion of tears, but dry eye can also arise because of problems with tear quality, rather than quantity.
Causes of dry eye in pets
A variety of dry eye causes exist, including:
- Immune-mediated — This is by far the most common dry eye cause, and occurs when your pet’s immune system attacks the lacrimal and third eyelid glands, resulting in inflammation and low tear production.
- Cherry eye — A cherry eye occurs when the third eyelid gland pops out of its normal location. Gland damage from exposure, or gland removal for cherry eye treatment, may reduce tear production, leading to dry eye.
- Genetics — Cavalier King Charles spaniels, English bulldogs, Lhasa apsos, pugs, shih tzus, and West Highland white terriers may be genetically predisposed to dry eye development.
- Miscellaneous causes — Sulfa drugs and other medications, certain neurologic or endocrine conditions, radiation therapy, infectious agents, or a congenital reduction or absence of tear glands may all lead to dry eye.
Signs your pet has dry eye
As the name would imply, the eye surface may appear dry or dull, rather than wet and shiny. Pets affected with dry eye may also have thick mucoid eye discharge, eye pain, or red eyes or conjunctiva. In many cases, both eyes will be affected to some degree.
Dry eye consequences for your pet
Pets with dry eye are at risk for painful corneal ulcers and infections, scarring, or abnormal pigmentation or vessel growth on the eye surface. These changes may impair your pet’s vision, or become severe enough that eye removal is necessary.
Methods to diagnose your pet with dry eye
Our Veterinary Vision Center team will conduct these tests if we suspect your pet has dry eye:
- Biomicroscopy — For this test, our ophthalmologist will use a handheld microscope with a light source to examine the eye surface, and the tear film, for visual abnormalities.
- Schirmer tear test — A paper strip called a Schirmer tear test will be placed between your pet’s eyeball and lower eyelid for one minute to quantify tear production.
- Tear film break-up time test — In cases where the Schirmer tear test is normal, but our ophthalmologist still suspects dry eye, a tear break-up time test may be used to detect tear quality abnormalities.
Treatment of dry eye in pets
Dry eye can rarely be cured, so most cases require lifelong management using the following options:
- Medication — Medications to decrease inflammation, lubricate the eye, and promote tear production can be combined, to keep the eye as comfortable and healthy as possible.
- Surgery — In cases that do not respond to medical therapy, our ophthalmologist can perform surgery to reroute the parotid salivary gland duct from the mouth to the eye, thus providing eye lubrication and moisturization from the saliva.
- Collaboration — Because some dry eye cases arise because of an underlying disease state or condition, our ophthalmologist may work with other veterinary specialists, or your family veterinarian, to develop your pet’s best treatment plan.
We may not know why some movies leave you a blubbering mess, but our Veterinary Vision Center team does know a lot about your pet’s tears. Contact us to set up an appointment with our board-certified ophthalmologist, so your pet doesn’t have to live with dry, uncomfortable eyes anymore.