The conjunctiva is the pink tissue lining the globe of the eye and inside the eyelids. Pink eye is inflammation of the conjunctiva and the medical term for pink eye is called conjunctivitis. Pink eye in people is most often a highly infectious, transmissible eye condition. However, dogs rarely have infectious conjunctivitis! The number one cause of conjunctivitis in dogs is allergic or irritant inflammation of the eye.
Conjunctivitis in dogs looks like a red irritated eye with red inflamed conjunctiva (the pink tissues that line the eye). There is often an ocular discharge that is tan to yellow in color.
A great product to apply to keep your dog’s eyes lubricated and healthy is Optixcare. It is recommended by veterinary ophthalmologists and can be used with other eye medications. It just needs to be applied 10 minutes before or after any other eye medication.
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Pink eye in dogs is different than pink eye in people!
The most common cause of conjunctivitis in the dog is allergic/irritant conjunctivitis and dry eye. Other less common causes of conjunctivitis in dogs are: conformational abnormalities in the eye, immune mediated causes, infectious causes (viral, bacterial), parasitic causes and traumatic causes.
In people the three most common causes of pink eye are: viral, bacterial and allergic. The vast majority of human pink eye cases in adults are caused by viruses. Specifically, the viral causes of conjunctivitis in adults are from adenovirus (65-90%) but herpes virus and Enterovirus can also cause pink eye. Bacterial pink eye in adults are usually Staphylococcus aureus, Streptococcus pneumoniae and Haemophilus influenzae.
In kids conjunctivitis is most often caused by bacteria. The most common bacterial causes of conjunctivitis in kids are due to Haemophilus influenzae, Streptococcus pneumoniae and Morraxella catarrhalis .
Less commonly allergens, toxins and local irritants can cause non-infectious conjunctivitis in people.
Causes of pink eye in dogs besides allergic/irritant causes
While allergic/irritant pink eye is most common in dogs, there are many other possible causes of inflammation of this tissue of the eye.
Conformational eye issues
Structural problems with the eye such as lower eyelids can roll open to cause irritation of the lining of the eye (called ectropion), eyelids can also roll inwards and cause eyelashes to rub on the eye (called entropion).
Immune mediated eye diseases
Some immune mediated diseases can cause marked redness and thickening of the conjunctiva. KCS is a condition where the immune system attacks the lacrimal gland that produces tears. This creates low tears and a very dry, irritated eye. KCS is treated with topical eye drops containing cyclosporine or tacrolimus.
Another immune eye condition is episcleritis which is inflammation of the thin outer layer of the white of the eye. It causes the whites of the eyes to look very injected and sometimes a pink lump can develop on the eye. Pannus is an immune mediated condition of the eye that causes pink inflammatory tissue to develop in the corners of the eyes and can spread. It is triggered in certain breeds of dogs (German shepherds) and is more prevalent in high altitudes and with increased UV light exposure. Pannus is a life-long condition but can be managed by immune modulating eye drops like cyclosporine or tacrolimus.
Bacterial causes of conjunctivitis
Primary bacterial causes of conjunctivitis are extremely rare in dogs. However, secondary bacterial infections occur frequently with other diseases of the eye. Bacteria is normally found in the conjunctival sac of normal dogs and rarely causes inflammation. The bacteria may proliferate if there is something that alters the normal homeostasis and allows for proliferation of bacteria. This is most often due to allergic or irritant trauma to the eye such as KCS.
Viral causes of conjunctivitis
Occasionally viruses can cause canine conjunctivitis. The most common viruses are canine herpes virus and canine adenovirus.
Although infectious conjunctivitis is rare in the dog, increased exposure to large populations of dogs and increased opportunities for exposure to infectious secretions and dogs with viral conjunctivitis typically have CHV-1 or CAV-2. CAV-2 infection typically causes a harsh cough along with conjunctivitis signs. THese signs typically last for about 2 weeks. Dogs are well protected from canine adenovirus because it is contained in our core vaccine for dogs (DAPP: distemper, canine adenovirus types 1 and 2, parainfluenza,and parvovirus). Canine herpes virus-1 is more likely to be a viral cause of conjunctivitis in dogs because there is no available vaccine for this virus . However most adult dogs have minimal to no upper respiratory signs. In some dogs it can cause moderate to severe conjunctivitis as well as irritation of the cornea.
Parasitic causes of conjunctivitis
Parasitic causes of conjunctivitis in dogs are rare. The nematode Thelazia is also called an “eye worm”. It is caused by filth flies feeding on eye secretions and then depositing eggs onto the surface of the eye. These can develop into many tiny worms that can be seen moving across the eye. This can be treated with oral milbemycin (found in some heartworm preventatives like Interceptor) or with medicated eye drops.
Traumatic causes of conjunctivitis
Strangulation can cause bilateral acute swelling of the conjunctiva. This can happen after dog fights or even after struggling with restraint with the leash. This type of scuffle can accidentally lead to acute subconjunctival bleeding due to an increased pressure in the blood vessels supplying the tissues.
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How pink eye is diagnosed in dogs
Conjunctivitis is diagnosed on a physical exam by the character of the conjunctiva which looks red, inflamed, and swollen. The underlying cause of conjunctivitis must be evaluated by ruling out other causes.
Dry eye, which is also called KCS, can be tested by checking a dog’s tear production. Tear production is measured by using a small paper strip and placing the tip of it inside the eyelid. The tears will wick down the paper. A normal tear production is at least 15mm of tears on the paper strip within 1 minute. A normal tear test will rule out dry eye. Dry eye is diagnosed in any dog whose schirmer tear test is less than 10mm in 1 minute and suspected with a tear test less than 15mm in one minute.
If KCS has been ruled out, a careful evaluation of the eyelids and around the conjunctiva is important. Some young dogs can have conformational changes that predispose them to a red irritated conjunctiva lining.
Examples are eyelid shapes that cause hairs near the eyelid to rub onto the cornea and cause irritation. This is called trichiasis.
There are also hairs that can grow in abnormal places like inside the corners of the eyelids.
This condition is called distichichia.
Some breeds of dogs have red inflamed conjunctiva from chronic exposure due to lower eyelids that sag. These dogs don’t always require treatment as the condition does not always cause discomfort.
Some dogs have lower eyelids that roll inwards. This is more likely to be uncomfortable as it can cause the hairs around the lower eyelids to rub on the eye and create irritation and cause secondary infection.
When evaluating a dog for conjunctivitis, your veterinarian will assess the eyelid confirmation, check the eye surface for any irritation from abnormally placed eyelashes, and look in the corners of the eyes and inside the lids for foreign bodies. They may measure your dog’s tear production with a schirmer tear test and following that they may stain the eye with a fluorescein stain (a bright yellow stain) that will highlight any defects or scratches on the clear part of the eye (cornea). Your veterinarian will look for any signs of allergic skin disease that might point to allergic conjunctivitis. Allergic conjunctivitis usually occurs with other signs of allergies in dogs such as paw licking and face rubbing.
How is pink eye treated in dogs
Pink eye in dogs is treated differently depending on the underlying cause. The most common cause of pink eye in dogs is secondary to allergies. Treatment for allergic conjunctivitis is with a combination antibiotic and steroid ophthalmic drop. This is most important in dogs that present with yellow eye discharge and eye rubbing.
For more mild cases of allergic conjunctivitis, a mild saline eye rinse can be used after coming indoors to gently flush away and offending pollen, dust and particulates etc. Gentle lubricating eye drops can soothe red irritated eyes. LINK
For dogs diagnosed with a condition called dry-eye (KCS) an eye drop to stimulate tear production and a lubricating eye drop is recommended. Typically this drop is either cyclosporine or tacrolimus.
Some dogs have recurrent conjunctivitis from eyelashes that rub on the eye. These conformational changes are best treated by corrective surgery to remove hairs growing where they shouldn’t (distichia) or to adjust the eyelid so hairs lining the eyelid don’t rub on the cornea.
Viral conjunctivitis is rare and typically self-limiting in dogs. However, occasionally viral conjunctivitis requires antiviral drops for best response.
How to prevent and treat pink eye in your dog at home
To prevent allergic conjunctivitis you can try to minimize contact with possible allergens . You can gently flush the eyes with a saline rinse 1-2 times a day after spending time outside (LINK). This can help to irrigate the eyes to remove any irritants like dust, pollen and debris. You can also apply antihistamine eye drops as needed. The best choice is over the counter Ketotifen found in Zaditor and Alaway drops. Avoid over the counter eye drops marketed to “take the red out” as they can contain naphazoline which stings and can cause rebound red eye.
If your dog is in contact with other dogs such as at a doggie daycare and comes down with an eye infection, it is best to consult your veterinarian to make sure it is not a rare infectious case of canine conjunctivitis.
How long does pink eye last in your dog?
If your dog is diagnosed with allergic or irritant conjunctivitis, it should respond quickly to topical steroid/antibiotic eye drops within a day or two. For home based treatments with eye flushes and topical antihistamine drops it can take a while longer like a few days to a week to see a response.
For dogs with a chronic condition like dry eye (KCS) or pannus, the response with immune modifying drops will take a few weeks.
Is pink eye contagious to other dogs and humans?
The most common cause of conjunctivitis in dogs is allergic or irritant and is not contagious to other dogs or people.
There are some rare viral causes of conjunctivitis like canine herpes virus and chlamydia (a bacterial infection) that can be shared in groups of dogs. Primary bacterial conjunctivitis in dogs is even more rare. There are rare reports of ocular chlamydial conjunctivitis in cats and guinea pigs being transmitted to people. However, there are no documented reports of pink eye from chlamydia in dogs passing to people.
Pink eye in people is most commonly viral and caused by human-specific adenoviruses and herpes viruses which do not infect dogs or cats.
Interpreting a “red eye” in your dog
When an eye looks “red” it may either be due to the conjunctival tissues looking red and inflamed or due to the vessels on the sclera (the whites of the eyes) being injected.
Injection of the blood vessels on the whites of the eyes is called episcleral injection and is typically associated with disease inside the globe of the eye such as glaucoma (elevated pressures in the eye) or decreased pressures inside the eye (uveitis).
Inflammation of the conjunctival tissues occurs more with surface ocular disease like KCS, allergic conjunctivitis or a superficial corneal ulcer.
Allergic conjunctivitis in dogs
A common cause for a red eye in a dog is allergic conjunctivitis. Most dogs with a normal tear production, normal eye pressure and no sign of irritation/ulceration of the cornea are suspected to have allergic or irritant conjunctivitis.
They often will have other signs of allergies like rubbing the face, itchy skin chewing paws etc. Symptoms may include conjunctival redness, mucoid eye discharge and possibly inflammation of the eyelids. Treatment with a steroid/antibiotic eye drop would quickly improve symptoms with hours to a few days (this is usually given three times daily). It is sometimes necessary to give for a few weeks and then tapered.
Follicular conjunctivitis in dogs
A form of allergic conjunctivitis is called follicular conjunctivitis It occurs most frequently in dogs under 18 months of age. Symptoms include conjunctival redness, mucoid to yellow mucus discharge from the eyes. The inside surface of the third eyelid will show marked redness with very prominent lymphoid follicles. This condition also responds well to topical steroids 3-4 times daily gradually tapered over 1-2 months.
Dry eye (KCS) in dogs
Dry eye is another common cause of red eyes in dogs, although not nearly as common as allergic and irritant causes.. Clinical signs of KCS are excess blinking, redness of the conjunctiva, yellow to yellow mucoid discharge from the eye, and a lackluster appearance to the surface of the eye. This is due to decreased quality and amount of tears. A schirmer tear test under 10 mm /min is consistent with KCS. Values of 10-15 are considered low but suggestive of KCS.
The most common cause of KCS in dogs is inflammation of the lacrimal gland. The condition is treated with immune modulating eye drops: cyclosporine or tacrolimus 2-3 times per day. It can take up to 3 weeks for the medications to improve tear production. In the meantime it is important to use lubricating eye drops like GenTeal Severe dry eye drops or Optixcare eye drops. A topical antibiotic may be used if there is bright yellow discharge suggestive of an infection.
Corneal ulcers in dogs
Any red eye should be stained with fluorescein stain by your veterinarian to assess the integrity of the surface of the eye (cornea). Ulceration of the cornea presents as a dog with a painful eye. They often blink and squint and may rub their eyes. Treatment of an uncomplicated superficial corneal ulcer (a shallow ulcer or defect on the cornea) will require topical antibiotics 3-4 times a day but should heal within a week.
Uveitis and glaucoma in dogs
Another cause of a red eye in a dog is problems with pressure within the eye. An elevated eye pressure is called glaucoma. Uveitis is a condition causing low eye pressure. An instrument called a tonometer is used to measure the pressure within the eye. It is a handheld unit that can quickly measure your dog’s intraocular eye pressures (IOP). A normal IOP is between 10-20mmHg in the dog. A dog with glaucoma will have an eye pressure typically above 30mmHg. Uveitis measures as a low eye pressure, typically well under 10mmHg. Dogs with glaucoma and uveitis have painful eyes and will often squint and blink.
Conclusion for pink eye in dogs
Pink eye in dogs is very different from the pink eye in people. This is because pink eye in dogs is generally not contagious to other dogs. It is most often secondary to seasonal allergies or from contact irritants.
A red eye in a dog can be from a number of causes, so it is best to have your dog evaluated by your veterinarian. They will be able to make sure the cornea is not damaged and that there is not an underlying condition to be addressed like a chronically low tear production or a more dangerous condition such as glaucoma or uveitis which causes changes in pressure within the globe of the eye.