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Ophthalmology is a branch of medicine that involves the diagnosis and treatment of eye disorders in people and in animals. There are many complexities associated with ophthalmology, so much so that boarded veterinary ophthalmologists are available for referrals from your general practitioner or GP veterinarian.
Some eye problems can be quite subtle in appearance whereas otherwise will cause overt changes to your dog’s eyes or vision. What are some of these diseases, and when might your regular veterinarian need to refer your pup to an eye specialist?
There are a number of eye diseases that can be passed on from parent to offspring. These inherited or genetic eye diseases are more likely to occur in purebred dogs, but it is still possible for mixed breed dogs to become affected. Glaucoma, Collie Eye Anomaly (CEA), Progressive Retinal Atrophy (PRA), and Keratoconjunctivitis Sicca (KCS) are examples of inherited eye disorders.
Dogs can develop eye infections just like people can. Bacteria, viruses, and even parasites can cause infections that result in redness, discharge and squinting. These can cause very sudden changes and are often easier to detect than certain inherited eye diseases.
Eye trauma is the most noticeable because you may notice your dog suddenly squinting a lot, or he may have more severe signs like bleeding into the eye. Trauma can result in chronic changes, including blindness if left untreated.
Blepharospasm is not an actual eye disease but is one of the most common signs to indicate that your dog is having an eye problem. If you’ve ever gotten something in your eye that caused a lot of discomfort, you’ve probably felt the urge to squint or close that eye. This is very similar to the kind of blepharospasm that dogs experience with eye swelling, irritation, and trauma such as corneal ulcerations. They will squint the affected eye or even experience spasmodic contractions of the eyelids.
Corneal ulcers (or scratches) are one of the most common causes of blepharospasm in dogs. Allergies, infections, and irritants such as smoke can also cause it. Physical problems likeentropion –which is when a dog’s eyelids roll inward – can irritate the eye. Secondary inflammation and trauma can also occur when dogs rub or paw at their eyes.
The opposite ends of your eye are known as thecanthi, where the canthus is closest to your ear is thelateral canthus and the one closest to your nose is themedial canthus. Located at the medial canthus and just behind the lower lid of your dog’s eye is a structure known as thenictitating membrane or third eyelid.
It is a structure that offers further protection to your dog’s eyes while hunting or fighting, and it contains a gland that is responsible for a large portion of the tear production to protect that eye.
In certain breeds, the small fibrous anchor that secures the third eyelid can become weak and causes the gland toprolapse or pop out. The prolapsed gland has a red appearance and thus earns the term “cherry eye.” Prolapsed third eyelids are common in Beagles, Boston Terriers, Shih Tzus, Cocker Spaniels, and English Bulldogs.
Surgical correction is necessary to correct this condition. The surgeon or veterinary ophthalmologist will tuck the gland back in to prevent further prolapsing. If left untreated, a prolapsed gland may stop production sufficient tears and will result in dry eye orKCSfor that eye. This is why the complete surgical removal of the gland is also not recommended.
KCS in dogs is also known as dry eye because the condition involves the lack of sufficient tear production. Tears are produced by glands around the eyes to protect the eyes from debris, bacteria, allergens, etc., and they help to lubricate the structures around the eye. Without sufficient tears, eyes can become reddened, dry, and painful. Thick green or yellow mucoid discharge develops due to the lack of the watery component in tears.
KCS can be inherited and affects many dog breeds such as Shih Tzus, Lhasa Apsos, Cocker Spaniels, Boston Terriers, English Bulldogs, Pugs, and Yorkies. There are also certain immune-mediated disorders that attack the tear glands and thus limit tear production. Viral infections like distemper and certain medications like sulphonamide drugs can also impair tear production.
KCS is easily diagnosed via Schirmer tear testing. A small piece of paper is placed near the lower lid of the eye, and then an assistant will close your dog’s eye. The paper is left in place for 60 seconds, and when tears are naturally produced, a small blue dye line on the metered paper strip will move downward.
If the dye line does not move past 15 millimeters, your dog may have a dry eye. Treatment involves the twice-daily use of an ointment to help increase tear production. Eye lubricants are also essential.
The pink tissues surrounding your dog’s eyes are known asconjunctiva, which are mucous membranes that protect the eye.
When these tissues become inflamed, this is known asconjunctivitis. Almost any eye problem can contribute to the development of conjunctivitis. Examples include the following:
Treatment is recommended based on addressing the underlying cause. Your veterinarian may recommend testing to rule out other conditions. These tests include the Schirmer tear test to rule out KCS,tonometry to rule out glaucoma and aneye stain test to rule out a corneal ulcer. If an infection is suspected, a topical antibiotic is usually prescribed.
Saline wash or eye irrigation solution can help with irritants, and sometimes oral medications are prescribed to help with infection and pain.
Theanterior chamber of the eye is located just behind the clear, frontmost part of the eye called thecornea and extends back to thelens which is a clear structure located just behind the colored part of the eye called theiris.
This chamber is filled with a fluid calledaqueous humor that comes from nearby blood vessels in theciliarybody and provides nutrients to the eye’s internal structures.
This fluid will constantly drain into the area between the cornea and iris known as theiridocorneal angle. When disorders disrupt the flow of humor, pressure builds up inside the eye. This is what is known as glaucoma.
Iris inflammation, lens dislocation, bleeding, trauma, and tumors are all possible causes for glaucoma, and many breeds of dog can be genetically predisposed to the development of glaucoma.
Dogs with clinical signs may seem painful around their eyes, develop watery discharge, have bulging eyes, or have eyes that suddenly appear cloudy. Immediate testing and treatment are necessary because, if left untreated, glaucoma can cause permanent blindness.
The lens inside of your dog’s eyes will stretch and shrink so that it can direct light onto the back part of your dog’s eye known as theretina. This is how vision works. When the lens becomes cloudy or opaque, vision can become impaired because it is no longer flexible and cannot direct light as well as it used to do.
Incipient cataracts are when less than 15% of the lens is affected.Immature cataracts are when more than 15% but less than 75% of the lens is affected, andmature cataracts are when the entire lens is affected.
Cataracts can be hereditary and commonly affect breeds like Labrador Retrievers, Cocker Spaniels, French Poodles, and Boston Terriers. Certain diseases like diabetes mellitus can also increase the risk of developing cataracts.
Left untreated, cataracts can cause permanent blindness. Most dogs can adjust well as the blindness slowly progresses, but in cases with diabetes, cataracts can develop quickly. Surgical correction is necessary for treatment as there are no medical treatments available.
With cataract surgery, the diseased lens is removed and an artificial lens is implanted. This type of procedure can only be performed by a veterinary ophthalmologist.
Eye diseases can cause very acute or sudden signs, and it is important to address them right away because blindness is a consequence of many of the disorders mentioned here.
If you are seeing blepharospasm, discharge, redness, swelling, or your pup is pawing at his eye, be sure to contact your vet right away. They may be able to perform preliminary tests and treatments or will need to refer you to a veterinary ophthalmologist for further care.
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Meet The Author
Dr. Erica Irish
Erica has worked in the veterinary field since 2006, starting out as a veterinary technician before graduating from the UF College of Veterinary Medicine in 2013. As a general practitioner in an animal hospital, she has many interests and is especially interested in dermatology, cardiology, internal and integrative medicine
