What Makes the Whites of Your Dog's Eyes Red?

By Jane Meggitt

If the whites of your dog's eyes turn red, get him to the vet as soon as possible. Red or bloodshot eyes can result from trauma, infection, allergies or eye diseases, requiring your vet to diagnose the cause. If there's no foreign particle in the eye or obvious scratch or ulceration, she'll conduct various tests based on a physical examination and related symptoms.

Canine Glaucoma

A red, painful eye is a primary sign of glaucoma, a serious eye disease. Caused by a sharp increase in internal eye pressure, glaucoma often results in blindness. Redness is often the earliest sign of the disease, so it's crucial for your dog's future vision to have a red eye examined promptly. Other symptoms include a cloudy eye, excess tear production, eye enlargement and a dilated pupil, unresponsive to light. Your vet diagnoses glaucoma by measuring the dog's intraocular pressure, using a Tono-Pen or other tests. If caught early, topical medication and possibly laser surgery can reduce the intraocular pressure and preserve vision. In advanced cases, surgery may be necessary, not to save sight, which likely is already gone, but to treat the intense pain connected with the condition.

Canine Uveitis

The uvea, containing blood vessels, is made up of three parts: the iris, the choroid and the ciliary body. When there's inflammation inside the eye, the painful uveitis results. Besides the reddening, it's obvious by his behavior that your dog's eye hurts. Your dog likely will keep his eye closed and will avoid light. Other signs include excessive tearing, cloudiness and bleeding from his eye. Some of these symptoms are similar to those of glaucoma, but uveitis is actually the opposite condition. In this disease, intraocular pressure is insufficient. Trauma, tumors, parasites and various bacteria and viruses can cause uveitis. Your vet will perform an aspirate of internal eye fluids, along with an ocular ultrasound. She also might test for diseases that cause uveitis. She'll prescribe topical medications, which may or may not stop the inflammation. Uveitis can turn into a chronic issue as scarring results in vision loss.

Keratoconjunctivitis Sicca

Keratoconjunctivitis sicca, often referred to as "dry eye," results from the cornea and its surrounding tissues drying out. The tear glands aren't producing sufficient moisture, so the eye turns red and painful. Other symptoms include a copious, thick discharge from the eye. Trauma, allergies, corneal ulceration and various diseases can cause keratoconjunctivitis sicca. Your vet likely will perform a Schirmer tear test to measure tear production, and stain the eye for ulcer detection. While dry eye sometimes resolves by itself, many dogs require daily, lifelong administration of artificial tears to keep the eye adequately moistened. You'll have to clean your dog's eyes every day.

Horner’s Syndrome

If the third eyelid prominently appears in your dog's eye and is swollen and red, your pet might have Horner's syndrome. Other symptoms include sinking of the eye, a constricted pupil and eyelid drooping. Although certain ailments can cause Horner's syndrome -- including ear infections, tetanus or muscle atrophy -- most cases have no known cause. Fortunately, if the syndrome isn't related to an illness, the Horner's syndrome should resolve by itself within several days.