When Your Pet Has Red Eye

Several conditions, including glaucoma or episcleritis, can present themselves as red eye in dogs and cats.

Some causes of red eye in a dog or cat are minor. Other causes can be more serious. By:
Some causes of red eye in a dog or cat are minor. Other causes can be more serious. By: C Jill Reed

“Red eye” is not a diagnosis in itself, but a description of what the eye looks like in response to illness or injury. It is an umbrella term that describes an eye that is reddened, inflamed and sore.

Some causes of red eye are minor, such as a mild irritant. However, other causes can be more serious, such as glaucoma that increases the pressure inside the globe, causing pain and possibly damaging eyesight.

Because the eye has limited ways it can respond to injury or ill health, several different conditions all present in the same way as “red eye.”

These conditions include:

If you notice your pet has a red eye, it is always best to seek veterinary advice.


The common factor, no matter what’s driving the condition, is a red-looking eye. The eye appears red and angry, with the white of the eye laced with thick, tortuous blood vessels against a pink, hazy background.

The pet may close the eye or seem protective of it as if it would hurt to be touched. The other symptoms vary according to the cause, from an itchy eye or a sticky discharge (conjunctivitis) to pain (uveitis) and headache (glaucoma).


Although conjunctivitis is the most common cause of red eye, it can happen for other reasons, as listed below:

  • Conjunctivitis — infection on the surface of the eye caused by allergy, irritation, infectious causes, trauma or autoimmune disease
  • Glaucoma — a buildup of pressure within the eye that causes swelling and pain
  • Episcleritis — inflammation of the blood vessels in the eye due to irritation or infection
  • Neoplasia — cancer affecting the eye, which makes it angry and inflamed
  • Uveitis — inflammation either due to trauma or as a response to infection elsewhere in the body


To work out the cause of the redness requires careful examination of the eye.

Your veterinarian will use an ophthalmoscope to closely examine the exact nature of the inflammation of the blood vessels on the white of the eye, including how deep and congested they are and how moveable the vessels are over the surface.

She will look inside the eye to check for inflammation of other structures such as the iris. It is also important to measure the pressure within the eye and check for conditions such as glaucoma. This is done painlessly with a device called a tonometer, the same instrument used by optometrists.


Once a diagnosis is reached, treatment is targeted at the conditions. For example:

  • Conjunctivitis — antibiotic eye drops applied into the eye 2 to 4 times daily
  • Glaucoma — eye drops to reduce the production of aqueous humor provide some relief; the gold standard treatment is surgical placement of a stent to allow aqueous drainage, the equivalent to taking the plug out of a sink filled by constantly running taps
  • Episcleritis — steroid drops to decrease inflammation causing the redness
  • Neoplasia — assessment by a specialist for the suitability of chemotherapy or surgery as a best course of action
  • Uveitis — steroid drops to decrease inflammation and possibly the use of oral pain relief to relieve discomfort


Red eye is difficult to prevent, but if your pet has a sore or red eye, always seek prompt veterinary advice to prevent the risk of permanent damage to the eye or his eyesight.


  • Small Animal Ophthalmology. Pfeiffer & Petersen-Jones. Publisher: WB Saunders. 3rd edition.


This pet health content was written by a veterinarian.

Dr. Pippa Elliott, BVMS, MRCVS

View posts by Dr. Pippa Elliott, BVMS, MRCVS
Dr. Pippa Elliott, BVMS, MRCVS, is a veterinarian with nearly 30 years of experience in companion animal practice. Dr. Elliott earned her Bachelor of Veterinary Medicine and Surgery from the University of Glasgow. She was also designated a Member of the Royal College of Veterinary Surgeons. Married with 2 grown-up kids, Dr. Elliott has a naughty puggle called Poggle, 3 cats and a bearded dragon.

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