Eye Disease Part Two: Feline Conjunctivitis


There are a myriad of reasons why your pet’s eye can appear red or swollen, but often a red eye involves conjunctivitis. This term refers to irritation or inflammation of the lining of the eye (both of the globe and the eyelids). If the conjunctiva is irritated, the eye may appear reddish, and have more prominent superficial blood vessels. Oftentimes, the eyelids will be swollen, and the eye may look swollen or have discharge coming from it. Conjunctivitis can be caused by several processes, including mechanical irritation (such as outside debris or an eyelash), allergies, infectious organisms, or inadequate tear production. Diseases that primarily affect the inside of the eye can also cause secondary conjunctivitis, especially if the eye is painful and the pet starts to rub at it. Treatment for conjunctivitis is not one-size-fits-all, and must be tailored to the underlying problem. It’s also important to recognize that conjunctivitis in cats is very different from conjunctivitis in dogs.

For our feline friends, conjunctivitis is typically due to an infectious cause. This is usually a virus, but the tissue can become secondarily infected by bacteria. Feline herpesvirus is far and away the most common infectious cause of conjunctivitis in cats. This virus is ubiquitous, and almost every cat will be exposed to it at some point in their life. Initially, cats with herpesvirus develop upper respiratory signs, such as nasal discharge and congestion, along with conjunctivitis. Other ocular signs can occur, including corneal ulceration and dry eye. Sometimes, scarring and adhesions can occur in the eye, which can lead to blindness. Cats may have a fever, be lethargic, and be less interested in eating. The signs are often more severe in kittens than adult cats. The viral infection can predispose to a secondary bacterial respiratory infection, which often causes thicker, cloudier, ocular and nasal discharge. In about eighty percent of infected cats, the virus will become latent after the initial illness. It will hide in nervous tissue, and can reactivate later. The virus may reactivate several times throughout the cat’s life. Sometimes the reactivation can be triggered by stress or another sickness, but sometimes there is not an obvious trigger. Usually subsequent flareups are less severe, and may be limited to ocular signs. During a period of viral reactivation, the affected cat will be actively shedding the virus, and may act as a source of infection for other cats.

Diagnosing feline herpesvirus can be challenging. Many of the available tests will be positive in asymptomatic cats which have be vaccinated. Additionally, infected cats may not be actively shedding the virus, and could have a false negative on a test. Oftentimes, a presumptive diagnosis is made based on a high degree of clinical suspicion.

Unfortunately, there is no complete cure for feline herpesvirus, including its ocular manifestations. In the short term, this illness is treated supportively. If systemic signs like fever or dehydration are present, some severely affected cats may need supplemental fluids or even hospitalization for more intensive care. For the specific ocular signs, treatment usually involves lubricants and topical antibacterials to treat or prevent bacterial infection. Longer term treatment for affected cats varies. Some oral and topical antivirals may be helpful, but are often expensive and need to be specially compounded. They are usually reserved for severely affected cats, and may be given for several weeks during flareups. L-lysine is an amino acid which may decrease viral replication, and has been recommended as a dietary supplement for cats with herpesvirus. In recent years, its efficacy has been questioned, but it is unlikely to cause any negative effects. For many cats with herpesvirus, occasional periods of runny eyes or a stuffy nose may be a part of life. There are several actions owners can take at home to make such cats feel more comfortable. Breathing in warm, humid air can help decrease congestion, so having the cat in the bathroom while a hot shower is running can be helpful. Additionally, since cats are very dependent on their sense of smell to eat normally, owners can offer more palatable or strongly smelling food. Warming food may encourage a finicky cat with a runny nose to eat.

If no additional signs occur, and they continue to eat and drink normally, additional therapy may not be needed. However, if the cat has not had herpesvirus-like signs before, or he or she does not improve within one to two weeks, or becomes worse, they should be seen by a veterinarian.

During flareups, affected cats should avoid contact with other cats if possible. Some carrier cats may shed the virus intermittently even when they do not show clinical signs of illness. If a cat has a history of herpesvirus, it is recommended that they do not go outdoors, as they could infect other cats. Ideally, they should not be kept in a household with young kittens or immune compromised cats.

There is a vaccination for feline herpesvirus, and it is typically part of the core vaccines that all cats should receive at the vet. The vaccine will decrease the severity and the length of clinical signs if a cat is exposed to the virus, but it does not always completely prevent infection. Therefore, even if cats are vaccinated for herpesvirus, it is advised to keep them away from other cats with active infections.

There are also several other infectious causes of conjunctivitis in cats. These include calicivirus, another common virus which can cause ocular and upper respiratory signs in cats. It can appear similar to herpesvirus, but often involves oral ulcerations as well. Treatment is typically supportive as well.

There are also primary bacterial causes of feline conjunctivitis, including one called Chlamydophila and one called Mycoplasma. Typically, these cause signs limited to the eyes, without the sneezing and respiratory signs of viral conjunctivitis. They are more common in young cats, or after the introduction of a new cat to the household. Typically, these diseases respond well to topical antibiotics.

For all of these diseases, prompt recognition of the underlying problem can be key to avoiding more problems down the road. If you are concerned that your cat has conjunctivitis, don’t hesitate to seek veterinary care! Additionally, tune in next time for more information about conjunctivitis in dogs.




Bentley, E. (2011). Common Feline Ocular Disorders. Western Veterinary Conference. Retrieved February 3, 2019, from https://www.vin.com/doc/?id=5183189.