June is Adopt A Cat Month, and here at the Schwarzman Animal Medical Center, we’re celebrating our feline friends with an entire month of blogposts devoted just to cats. Last week, we explored Pandora Syndrome. This week, we’re turning our attention to a common and concerning issue in cats: red eyes.

Red eyes can result from any number of medical issues, which I will detail below.

Core Vaccines Can Help Prevent Red Eyes

Keeping your cat’s upper respiratory vaccines up to date is an important first step in preventing red eyes—especially those caused by infections. The core vaccine known as FVRCP helps to prevent viral causes of red eyes, such as:

• FVR stands for feline viral rhinotracheitis which is caused by a herpes virus, a major cause of conjunctivitis in cats (inflammation of the membrane around the eye).
• C stands for calicivirus, the other major cause of conjunctivitis in cats.

A Non-Core Vaccine To Help Prevent Red Eyes

Another cause of feline conjunctivitis is a bacterium known as chlamydia. While there is a vaccine for chlamydia, it’s not a core vaccine. Non-core vaccines are administered selectively, after consideration of exposure risk, including geographic distribution of the disease and the lifestyle of the cat. The chlamydia vaccine does not offer as much protection from infection with chlamydia as the FVRCP vaccine does against herpes and calicivirus, but it can be useful in multi-cat household to control chlamydia outbreaks.

Red Eyes Can Be Painful

The photo above shows my patient, Aldous. Notice his two pupils are different sizes. That’s because he has a painful right eye from a corneal ulcer. The ulcer likely developed from a viral infection and was further complicated by his chemotherapy. While Aldous appears to have his eyes open in the photo, most cats with corneal ulcers squint or keep their eyes shut due to pain. They also frequently have ocular discharge.

Red Inside the Eye: An Emergency

While viral infections and corneal ulcers tend to cause redness on the white of the eye (the sclera), redness inside the eye is more serious and often caused by hemorrhage. This is a bona fide emergency.

Redness within the eye can signal:

• Severe hypertension (high blood pressure)
• Inflammation inside the eye (uveitis)
• A possible tumor inside the eye

High blood pressure is easy to diagnose with a little cuff on your cat’s paw. However, if high blood pressure is not the cause, then an ultrasound of the eye may be recommended to make a diagnosis.

When Red Eyes Are Normal

The one situation where a “red eye” is normal is when your cat’s eyes reflect the light or a camera flash just right; the red you see in that situation is the normal color of the back of their eyes.

More on Red Eyes in Cats and Dogs

If you want to expand your knowledge about red eyes, watch AMC’s board-certified ophthalmologist, Dr. Sandra van der Woerdt discuss the issue in both cats and dogs.