What Causes Red Eye In Dogs?

What’s causing your dog’s eyes to turn red? It could be something as simple and easily remedied as allergies, or it could be much more serious, like in cases of glaucoma. There are several things that might cause the whites of your dog’s eyes to turn red, even cases of disease in other places in the body can lead to an inflammation in the eye. The best way to get a diagnosis is to see your vet, especially if you notice the redness sticking around for more than 24 hours.

A vet will have the diagnostic tools necessary to pinpoint exactly what is going on with your dog’s eyes. Take note, and let your vet know if you notice any discharge or watery eyes accompanying the redness.

Symptoms of Red Eye in Dogs

Redness is usually a symptom itself of some other issue, but you may notice some of the following along with it:

– Pawing at or rubbing eye on floor
– Squinting in light
– Keeping eye closed
– Cloudy eye surface
– Watery tearing eyes
– Red mass appearing from under the eyelid
– Red spot on the white of the eye
– Swelling or puffiness of the eyelids
– White or green discharge from inner corner of the eye

Causes of Red Eye in Dogs

 – Allergies – Irritation of the eye due to an allergen such as pollen, weeds, dust or fiber.
 – Conjunctivitis – Inflamed conjunctiva (the thin transparent tissue that covers the outer surface of the eye) due to irritants, allergies or infection.
 – Keratoconjunctivitis sicca (KCS) – Also known as dry-eye syndrome. Redness is due to inadequate tear production.
 – Entropion – The eyelid turns inward causing the eyelashes and eyelid to rub against the eye’s surface.
 – Cherry eye – A gland inside the third eyelid becomes inflamed and protrudes out from behind the eyelid. Appears as a small red bump poking out from below the eye.
 – Hyphema – Injury to the eye causes blood to pool in the front part of the eye.
 – Foreign body – Material or small particle trapped in the eyelid or on the eye surface irritates the eye.
 – Corneal ulcer – An open sore on the outer layer of the cornea, often caused by infection. Glaucoma – Increased pressure within the eye.
 – Uveitis – Inflammation of the iris or ciliary body caused by injury, infection or cancer.
 – Blepharitis – Inflammation of the eyelid due to infection, irritation or allergy.
 – Tumor– Benign or malignant mass growing behind or within the eye.

Diagnosis of Red Eye in Dogs

Should you see any redness in one or both eyes, pay a visit to your vet so they can tell you exactly what is causing it. The most common causes are conjunctivitis, allergies, and irritants, but it could be something more serious (see above.) Your vet will want to know when the redness began, how it has progressed, and whether your pet has been showing any signs of pain or irritation.

Ophthalmologic Exam

Your vet will likely conduct a full eye exam, which will inspect the parts of the eye including the conjunctiva, cornea, tear ducts, retina, and eyelids. Your vet may perform any of the following tests to get their diagnosis:

Schirmer Tear Test

A Schirmer tear test examines your pet’s tear production and helps rule out KCS or dry-eye syndrome. This test involves placing a small paper test strip in between the eyelid and the eye. The strip acts as an irritant, causing tear production. The tears are absorbed into the paper strips and a scale on the paper measures the level of tear production.


This test is often used to screen for glaucoma, a disease associated with abnormal eye globe pressure. The surface of the eye may be numbed prior to this test, though it is not required. A tonometer pen uses a small plastic ball that bounces quickly on and off the surface of the eye and measures the pressure. Several measurements may be taken to obtain an average.

Fluorescein Dye

This yellow-green dye is dropped onto the eye surface. Areas of damage to the surface of the eye light up (fluoresce) when a black light is shone onto the eye. This dye can indicate scratches and corneal ulcers.

Blood Diagnostics

Several underlying issues may cause the appearance of red eyes. Blood screening can measure kidney function, liver function, hormone production, hydration and electrolyte imbalances.

Treatment of Red Eye in Dogs

Once your vet has determined what is causing your dog’s eye redness, they’ll treat accordingly.

Topical Medications – These will include ointment or drops that may need to be given up to three times a day until symptoms stop. These could be antibiotics, steroids, pain relievers, dilators or artificial tears.

Oral Medications – Should your vet see that your dog has an infection, or trauma, oral antibiotics or anti-inflammatories might be prescribed. They may also prescribe an oral medication to address an underlying disease.

Surgery – Some cases, like cherry-eye, may require surgery to try to “manually reset” the gland. If it reappears after surgery, another surgery may be scheduled to permanently repair the issue. In some extreme cases, the redness may be untreatable and require surgical removal of the eye. It’s less complicated than it seems, and usually dogs get along just fine with only a loss of a little depth perception.

Recovery of Red Eye in Dogs

Your vet may recommend that your dog wear a cone, and request follow-up eye exams to evaluate how your dog is responding to treatment, but with correct use of any prescribed medication, your dog should recover wonderfully.


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