Cat eye infections can be caused by both viruses and bacteria. Two pathogens (one virus and one bacteria) cause the majority of all pink in cats: herpes virus and chlamydophila. With appropriate treatment, most feline eye infections will improve in 1-2 weeks. This article will teach you to understand what eye signs are likely to need prompt attention by your veterinarian and what signs mean that you can manage things at home with some tools and tips.
There are many possible causes of eye discharge and infection in cats. The number one cause is a viral infection with herpes virus. In cats under the age of 5, a bacterial infection with chlamydophila is the number two cause. Treatment may or may not be necessary depending on how comfortable your cat’s eyes are and if there is clear or colored eye discharge.
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Feline herpes virus affects almost all cats and is not contagious to people
The most common cause of all cat eye infections and upper respiratory tract infections is due to cat herpes virus: feline herpesvirus-1 (FHV-1). Feline herpes virus is distinct from human herpes virus and you will not catch herpes from your cat!
Studies have shown that 95% of all cats worldwide have been exposed to this virus and that 80% of cats are carriers of the virus! Although most cats are considered asymptomatic (latent) carriers of the virus, some cats will develop symptoms of upper respiratory infection with the virus. Signs include sneezing, nasal congestion and eye discharge with conjunctivitis (swelling and infection of the pink tissues that line the eye). Core vaccinations for cats include protection against feline rhinotracheitis virus (which is feline herpes virus). However, the vaccine does not prevent infection or relapse of infection It does reduce viral shedding and severity of disease signs.
Feline herpes conjunctivitis/ eye discharge typically develops as an acute onset of symptoms in kittens or young adult cats. Owners will report sneezing, eye discharge, conjunctival swelling and/or nasal congestion.
Types of eye discharge in cats: What clear, yellow, red and brown cat eye discharge means
Conjunctivitis generally affects both eyes and causes redness of the conjunctiva, and clear to mucoid eye discharge initially. If the eyes become infected secondarily with bacteria, the discharge will turn yellow to green in color.
Yellow infected eye discharge and conjunctivitis
Sometimes the watery discharge from herpes virus infection will look red tinged in color and dry dark brown with brown crusting in the corners of the eyes. This is due to normal pigmented compounds secreted in cat tears. Cats may spill more tears secondary to swelling and partial/complete closure of the duct that drains tears into the nasal passages.
Reddish brown tears from mild herpes viral infection
Cats with mild infections will have clear eye discharge or dried brown crusty discharge. They can have mild congestion and sneezing that does not impact their desire to eat or play. These cats can be monitored at home. As a general rule your cat does not have to be separated from other cats in the home because most cats are already exposed. The typical course of the illness is expected to last 10-14 days.
How do you know when to bring your cat to the vet with an eye infection ?
Occasionally herpes viral infection can cause ulcers on the cornea. The cornea is the clear part of the eye and ulcers are small fissures or defects on the surface of the cornea. Corneal ulcers are painful and can worsen with secondary bacterial eye infections. The classic herpetic ulcer causes filamentous branching on the corneal surface that is visible with a special rose bengal stain applied to the eye. If you see your cat squinting, blinking a lot, or rubbing their eyes you should bring your cat for an exam right away. If your cat has yellow or green discolored eye discharge you should bring your cat to the veterinarian’s office as this is a sign of a secondary infection in the eye.
Ocular complications of herpes virus in kittens
Very young kittens infected with the virus may develop a condition called symblepharon. Symblepharon occurs when the conjunctiva scars down to the eye because of inflammation. This can lead to decreased eye mobility and blockage of the nasolacrimal duct: the pathway for tears from the corner of the eye into the nose. Symblepharon should be treated by a veterinary ophthalmologist for best results.
Cause of excess tearing in cats: epiphora
A long-term outcome in some cats secondary to herpes viral infection is closure of the nasolacrimal duct. If there is a lot inflammation in the eye with an eye infection, this can close the duct. The nasolacrimal duct directs tears from the eye down into the nose. If there is sufficient inflammation from conjunctivitis it can close down this channel and lead to over flow of clear tears onto the face.
This condition is a benign condition because there is no serious complication if the excess tears don’t flow down the nasolacrimal duct. Excess tearing is called epiphora and can be treated for a better cosmetic outcome. To address the blocked duct it is best to see your veterinarian or a veterinary ophthalmologist. A fine gauge catheter can be directed into the duct to gently open it back up.
Epiphora: excess tearing in a cat due to blocked nasolacrimal ducts.
Herpes viral infection in cats: how it’s spread
Initial infection is spread via aerosolized droplets from sneezing, sharing saliva with food/water bowls, grooming or via sharing blankets, toys etc that carry the virus. Catteries and shelters commonly spread respiratory infections among cats due to close proximity. It’s not unusual to adopt a cat or kitten from the shelter with an upper respiratory tract infection or a cat or kitten who was recently treated for such.
Feline herpes develops after initial infection or due to a relapse of the latent carrier stage to an active infection. Triggers for relapse are not completely understood, but stress is considered a major cause. If you bring a new kitten or cat home from the shelter and your cat at home develops symptoms of sneezing, congestion and tearing it may not be due to infection from the new kitten. Stressful events, such as introducing a new pet to the home can lead to reactivation of a latent infection.
Treating feline herpes virus at home
Cats that have herpes viral flares may be best managed in low stress environments. Providing vertical spaces (cat trees, tall furniture to sit on) to relax on, keeping access to litter and food easy. Providing calming supplements such as Zylkene capsules (powder that is sprinkled over food) and plugging in calming feline pheromone diffusers like Feliway can be helpful.
Frequent application of high quality artificial tears can also be useful. Products that contain hyaluronate such as Optix care lubricating gel are recommended.
Supplementation with an amino acid called L-lysine is used in cats with herpes virus as a means to reduce viral replication. The dose in an adult cat is 500mg of L-lysine twice a day in adult cats with acute symptoms. The dose is 250mg twice daily in kittens. The jury is out whether supplementation actually works in cats. However, the product is an amino acid so it’s use is benign.
Antiviral therapy for herpes eye infections in cats
With severe or chronic FHV-1 topical antiviral drugs are sometimes prescribed. A good anti-viral eye drop is called Cidofovir 0.5% and is applied twice a day for up to three weeks as needed. Systemic antivirals can also be utilized. Famciclorvir is safe and effective oral antiviral for treating FHV-1 conjunctivitis and is given twice a day.
Bacterial eye infections in cats: chlamydophila felis
The second most common cause of infectious conjunctivitis is a bacterial infection called Chlamydophila felis. Chlamydophila felis is a bacteria that is endemic in cats and can infect the conjunctiva and nasal passages. The disease is spread via airborne transmission or contact with infected cats or fomites. The disease is rarely seen in cats over the age of 5 because of acquired immunity with age. Chlamydophila is typically one sided (unilateral) at first and causes more marked conjunctival swelling than feline herpes. Cats with chlamydophila have mainly eye signs unlike herpes virus which can cause a host of upper respiratory signs.
How chlamydophila looks different than cat herpes virus
- Cats’ with chlamydophila have fewer: symptoms conjunctivitis and mild nasal congestion.
- The conjunctival swelling seen with chlamydophila is more severe than with FHV-1.
- Chlamydophia does not cause corneal ulcerations
Diagnosis of chlamydophila is typically based on exam findings and response to an appropriate antibiotic therapy.
Treatment for chlamydophila eye infection in cats
Unlike herpes virus, chlamydophila infection does not cause corneal ulcerations. The treatment of choice for chlamydophila is an oral antibiotic given for the recommended duration (usually 3-4 weeks) to clear the organism completely. Oral antibiotic choices are often doxycycline at 5mg/kg twice daily for 28 days or amoxicilin- clavulante at 12-25mg/kg twice daily for 4 weeks. Ophthalmic antibiotic preparations can be helpful as well. Erythromycin ophthalmic (a human ophthalmic) and terramcyin ophthalmic (a veterinary ophthalmic). Terramycin ophthalmic is a tetracycline based ointment which has great efficacy against chlamydophila, however it also has polymyxin B which has been implicated in some rare but serious adverse effects in cats.
Eyelid agenesis in kittens causing conjunctivitis
Other possible causes of eye discharge that are not infectious are conformational changes (inherited) changes. Some kittens are born with incompletely formed upper eyelids (eyelid agenesis) that can lead to hair around the eye rubbing on the cornea. Over time this can cause inflammation, tearing and sometimes ulceration of the cornea with infection. Chronic rubbing of fur on the eye can cause scarring of the cornea. When hair rubs on the eye it is called trichiasis. Surgery of the upper eyelid or cryotherapy to ablate the hairs on the margin of the eye can be performed to correct the trichiasis.
Eyelid agenesis kitten causes trichiasis
Severe conjunctival swelling in cats: eosinophilic conjunctivitis
Another possible cause of severe conjunctival swelling is a rare condition called eosinophilic conjunctivitis. Eosinophilic conjunctivitis is characterized by unilateral or bilateral conjunctival redness, thickening and discharge. It is immune mediated and diagnosed by conjunctival scrapings that show allergy cells (eosinophils) infiltrating the conjunctival tissue. Treatment relies on topical corticosteroids such as 1% prednisolone acetate.
If your cat has evidence of an eye infection or swollen conjunctival tissues it’s always best to have your veterinarian examine your cat. Your vet can help determine the significance of the problem and provide a treatment plan for your cat.