Red eye in dogs and cats may signal many inflammatory conditions and infectious diseases:

Conjunctivitis – inflammation of the mucous membranes of the eye-is the most common eye disease of all domestic animals,” says Dr. Ralph Hamor, veterinary ophthalmologist at the University of Illinois Veterinary Medicine Teaching Hospital in Urbana. Dogs with allergies and purebred cats are prone to conjunctivitis. The eye reddens because of the increased flow of blood, and you may see swelling of the mucous membranes. Viruses or bacteria may cause conjunctivitis; parasites (such as ticks) and allergies are less common causes. Ticks can transmit several parasites that can cause Conjunctivitis, Keratitis and Uveitis (3). Discharge may be clear or contain mucus, depending on severity of the infection.

Keratitis- “Chronic superficial keratitis, also know as degenerative pannus, occurs primarily in German Shepherds but occasionally in other breeds,” says Dr. Paul Gerding, also a veterinary ophthalmologist at the teaching hospital. “The disease causes pigmentation and superficial blood vessels on the eye. It’s not that painful but can decrease vision if left untreated.

Keratitis also occurs in chronic cases of keratoconjunctivitis sicca (KCS). KCS occurs when there is not enough moisture in the tear film. A thick, ropy mucous discharge is associated with this common ophthalmic disorder. In chronic cases, the corneal layer of the eye becomes infiltrated with blood vessels, pigmented, and harder because of the long-term irritation. Treatment involves tear stimulants and anti-inflammatories. “Eye ulcers are often associated with keratitis and may require surgical repair,” adds Dr. Gerding.

In the case of external eye diseases such as conjunctivitis, keratoconjunctivitis sicca (KCS) and superficial corneal ulcers, eyedrops containing an antibacterial agent are often prescribed. Several daily instillations of eyedrops over several days are required for successful treatment. Eyedrops have several disadvantages, the biggest one being rapid elimination of the drug from the corneal surface. To overcome the disadvantage of repeated instillations, scientists have developed a soluble bioadhesive ophthalmic drug insert (BODI) that can be placed in the lower cul de sac of the eye. This BODI reduces the treatment to a single application and improves the efficiency of the treatment.
Inflammation of the eyelids and cherry eye – Eyelids may become inflamed from dermatitis; a bacterial, parasitic, or fungal infection; a metabolic or immune system problem; neoplasia; trauma; or sun damage. Treatment varies by exact diagnosis.

“Cherry eye” is a prolapse of the gland of the third eyelid. It commonly affects young dogs, especially beagles, cocker spaniels, Pekingese, and bulldogs. “The gland protrudes and becomes irritated and inflamed,” explains Dr. Hamor. “If one eye has cherry eye, the other eye could be predisposed to it as well.” Treatment for cherry eye is surgical replacement of the gland.