Red eye is a non-specific sign of inflammation or infection. It may be seen with diseases of the external eyelids, third eyelid, conjunctiva, cornea, and sclera. It may also occur with inflammation of the structures inside the eye, with glaucoma (high pressure within the eye) or with certain diseases of the orbit (eye socket). Either one or both eyes can become red, depending upon the cause of the problem.
Eyes become reddened when blood vessels of the conjunctiva (the pink lining of the eyeball and eyelids), sclera (white covering of the eye), or cornea (clear surface of the eye) become enlarged or more numerous.
What to Watch For
Redness of the eye or structures around the eye
Squinting, increased blinking, holding the eye closed
Pawing or rubbing at the eye
Possible decrease in vision or blindness
Possible cloudiness of the eye
Tearing or discharge from the eye
Possible systemic signs if the redness is associated with some sort of illness
Diagnosis of Red Eyes in Cats
Veterinary care includes tests to diagnose the condition causing the red eye and to define subsequent treatment. Your veterinarian will do a complete medical history and physical examination to try to determine if the problem involves only the eye(s) or if other changes are present in the animal.
A complete ophthalmic examination is required to determine the source of the redness and whether it involves inflammation of the external structures of the eye or the internal structures. Your veterinarian may refer your cat to a veterinary ophthalmologist for further evaluation using specialized instrumentation. The following tests may be performed during the eye examination:
Schirmer tear test to measure tear production
Fluorescein staining of the cornea to check for ulcers
Tonometry to measure the pressure within the eye
Examination of the interior of the eye under magnification
Taking scrapings of inflamed tissues (such as conjunctiva and cornea) for cytologic studies to determine the type of inflammation present
Examination of scrapings of the eyelids to look for parasites
Submission of samples for culturing bacteria and other agents
Biopsy of masses around the eye
Other tests may include:
A complete blood count and biochemistry profile if any systemic signs are present
Blood testing for the tick borne rickettsial and bacterial infections, for fungal infections and parasitic conditions, if the red eye is related to inflammation of the interior of the eye
X-rays of the chest and abdomen if an underlying systemic illness is suspected
Treatment of the Red Eye in Cats
The goal of therapy is to decrease any inflammation present and to address the underlying cause. It is very important that the cause of the inflammation or infection be diagnosed, so that specific treatment can be started.
Anti-inflammatory medication. The are two basic classes of topical anti-inflammatory medications that may be used to treat red eyes: nonsteroidal anti-inflammatory drugs and topical corticosteroids. These medications are not indicated when corneal ulcers are present or during active herpesvirus infections, and must be chosen based on the underlying ocular condition.
The nonsteroidal anti-inflammatory drugs (NSAIDs) are agents similar in action to ibuprofen. They are beneficial in some forms of red eye and not in others. They are less potent than the topical corticosteroids.
The topical corticosteroids are used most commonly for conjunctivitis, anterior uveitis and some forms of corneal inflammation. A number of these drugs exist and have varying degrees of potency.
Systemic anti-inflammatory medications. Occasionally systemic anti-inflammatory medications are used in conjunction with topical medications. These include antihistamines for the treatment of allergic conditions, oral NSAIDs to alleviate pain and inflammation inside the eye, and oral corticosteroids. The use of these products depends on the underlying cause of the red eye. It is important to note that systemic corticosteroids should not be used if infectious diseases (such as feline herpesvirus, fungal infections, etc.) are the source of the redness.
An Elizabethan collar may be applied to prevent rubbing or pawing at the eye.
An antibiotic or antiviral eye medication may be administered to treat or prevent infection.
Lubricant eye drops or ointment are sometimes given to protect the surface of the eye.
Swollen tissues may respond to warm, wet compresses.
Other treatments may be administered, depending upon the underlying cause.
Home Care
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up is important and may include the following:
Administer prescribed medications as directed and alert your veterinarian if you are experiencing problems treating your pet.
Ensure that your pet does not rub at the eye and cause more serious injury. If an Elizabethan collar is provided, have your pet wear it at all times.
Observe the eye closely. Signs that may indicate a worsening condition include more obvious redness, increased or altered discharge, pain or loss of vision. Blindness in just one eye may not be obvious, because the animal may behave normally when only one eye is affected.
The vertical white line in the center of this cat's cornea is a healing laceration. Note the blood vessels and scar tissue around the wound. Photo provided courtesy of Dr. Rhea Morgan.
Chlamydia psittaci may cause conjunctivitis and is also frequently associated with signs of URI. The disease may initially begin in one eye and later affect both eyes. Photo provided courtesy of Dr. Rhea Morgan.
