Introduction
Feline conjunctivitis refers to inflammation of the conjunctiva, which is the thin transparent tissue that lines the inner eyelid and covers the white part of the eye. It is a common eye condition in cats and can cause symptoms like discharge, redness, swelling and squinting. Eye discharge is one of the most noticeable signs of conjunctivitis in cats.
There are several potential causes of conjunctivitis in cats including infections from bacteria, viruses or fungi, irritation from foreign objects or allergies, and anatomical defects. Some causes like herpesvirus tend to result in chronic or recurring conjunctivitis. Diagnosis involves evaluating the cat’s history and doing tests like a fluorescein stain to assess damage to the cornea. Treatment depends on the underlying cause but may include antibiotics, antivirals and corticosteroids.
While conjunctivitis can cause discomfort, most cats respond well to treatment and complications are rare. Maintaining good hygiene and reducing exposure to irritants can help prevent conjunctivitis flare-ups. This article will provide an overview of the common causes of eye discharge and conjunctivitis in cats as well as diagnosis, treatment and prevention recommendations.
Causes of Eye Discharge in Cats
There are several potential causes for eye discharge in cats, but most commonly it is due to some type of infection or irritation.
Bacterial Infections
Bacterial conjunctivitis is one of the most common causes of feline eye discharge. It occurs when bacteria infect the conjunctiva, which is the thin membrane lining the inner eyelids and front of the eyeball. Common bacteria that can cause conjunctivitis in cats include Staphylococcus, Streptococcus, and Chlamydophila species. Symptoms include yellow, green, or white eye discharge, redness and swelling of the conjunctiva, and squinting or blinking. Bacterial conjunctivitis is very contagious between cats, so isolation may be necessary (source).
Viral Infections
Upper respiratory infections caused by viruses like feline herpesvirus and calicivirus can also lead to conjunctivitis and eye discharge. The discharge is often clear and watery. Additional symptoms may include sneezing, coughing, ulcers on the cornea, and fever. Like bacterial infections, viral conjunctivitis is highly contagious between cats (source).
Fungal Infections
Fungal infections are less common but can cause eye discharge, irritation, and corneal ulcers in cats. Cryptococcus is one genus of fungus that may be responsible. Fungal infections often occur secondary to another condition that has weakened the immune system (source).
Parasitic Infections
Certain parasites like Toxoplasma can cause inflammation in the eyes of cats leading to discharge. Kittens and cats with weakened immune systems are most at risk. Additional symptoms may include vision problems, dilated pupils, and retinal damage (source).
Bacterial Conjunctivitis
One of the most common causes of yellow or greenish eye discharge in cats is bacterial conjunctivitis. This type of conjunctivitis is caused by bacterial infections, often from microorganisms like Chlamydia or Mycoplasma (Bacterial Conjunctivitis in Cats – Veterinary Partner – VIN).
With bacterial conjunctivitis, the discharge will typically be yellowish or greenish in color. This is because the eye produces more mucus in response to the bacterial infection. The increased mucus mixes with tears, debris, and dead white blood cells, resulting in the discolored discharge.
In addition to the yellow/green eye discharge, other symptoms of bacterial conjunctivitis include redness, swelling and irritation of the eyes and third eyelid, eye pain, and squinting or blinking frequently. If left untreated, ulcers may form on the cornea.
Bacterial conjunctivitis is very contagious between cats. It can spread through direct contact or by exposure to respiratory droplets from an infected cat. Cats with weakened immune systems are more susceptible.
Viral Conjunctivitis
Viral conjunctivitis in cats is often caused by feline herpesvirus (FHV-1) or feline calicivirus (FCV) (VCAH). These highly contagious viruses can spread rapidly between cats. The most common signs of viral conjunctivitis include:
- Excessive tearing or watery discharge from one or both eyes
- Squinting or spasmodic blinking
- Redness of the moist tissues of the eye
- Clear, mucoid, or purulent ocular discharge
The watery eyes associated with viral conjunctivitis are often the result of impaired tear drainage due to inflammation and swelling of the nasolacrimal drainage system. This allows tears to overflow onto the face. Discharge may start out clear but can become mucopurulent as secondary bacterial infections occur.
Viral conjunctivitis is highly contagious to other cats. The viruses are spread through direct contact with ocular or respiratory secretions from infected cats. Indirect spread can also occur from exposure to contaminated objects like food bowls, bedding, or grooming tools.
Allergic Conjunctivitis
Allergic conjunctivitis is inflammation of the conjunctiva caused by an allergic reaction, often to pollen, dander, dust mites, or other irritants in the environment (source). In cats with allergic conjunctivitis, the immune system overreacts to the allergen, causing inflammation and irritation of the eye. Allergic conjunctivitis is one of the most common causes of eye discharge in cats.
The main symptom of feline allergic conjunctivitis is clear, thin, stringy eye discharge. The discharge may be watery and may cause the cat’s eyes to tear excessively (source). There may also be itchiness, redness, or swelling around the eyes. Unlike conjunctivitis caused by infection, allergic conjunctivitis does not usually cause cloudy or pus-like discharge.
To diagnose allergic conjunctivitis, your vet will rule out other causes of eye discharge like infection or injury. They may recommend allergy testing to identify the specific allergen triggering the reaction.
Fungal Conjunctivitis
Fungal conjunctivitis is relatively rare in cats, accounting for less than 10% of conjunctivitis cases. It is caused by a fungal infection, most commonly the ringworm fungus Microsporum canis. Ringworm is highly contagious and can spread between cats and other animals. The fungi attack the cornea, conjunctiva, and eyelids, leading to irritation, redness, swelling, and discharge. Thick, cottage cheese-like discharge is characteristic of fungal conjunctivitis.
According to https://veterinaryvisioncenter.com/feline-fungal-ocular-disease-what-cat-owners-should-know/, “Histoplasmosis, which is caused by Histoplasma capsulatum, is the second-most common systemic fungal disease in cats. Transmission occurs when a cat inhales the fungal spores.” Fungal infections can spread systemically in cats if left untreated.
Other Causes
Foreign bodies lodged in the eye can also cause yellow discharge. Debris, dust, dirt, seeds, or plant material can become stuck in the eye, irritating the conjunctiva and leading to infection. Cats with long fur are prone to getting foreign material trapped in their eyes. If you notice your cat squinting, pawing at their eye, or having trouble keeping it open, inspect for any debris stuck in the corner of the eye or eyelids.
Eye injuries are another cause of yellow discharge in cats. Blunt trauma, scratches, or puncture wounds can damage the cornea and surrounding structures. This allows bacteria to enter and infect the eye. Signs include pain, excessive blinking, squinting, swelling around the eye, and yellow/green discharge. Seek veterinary care immediately if you suspect an eye injury, as prompt treatment is needed to prevent vision loss. According to [the American College of Veterinary Ophthalmologists](https://www.acvo.org/new/public/eye_problems/corneal_ulcers.shtml), “50% of feline corneal ulcer patients with appropriate medical therapy regain vision, whereas less than 25% of untreated corneal ulcers heal normally.”
Diagnosis
To diagnose the cause of eye discharge in cats, veterinarians will first perform a thorough physical exam of your cat’s eyes. They will look for signs of inflammation, ulcers, or other abnormalities. The vet may stain the eye with a fluorescein dye to check for ulcers on the cornea. They will also evaluate the color, consistency and quantity of the eye discharge.
Cultures may be taken from the eyes to identify a bacterial or fungal infection. Conjunctival scrapings or cytology of the discharge can also be performed. Biopsies of the conjunctiva may occasionally be needed to check for cancer or other problems.
Cats with viral or allergic conjunctivitis may have corneal ulcers identified with the fluorescein dye. Bacterial infections will show up on cultures while fungal infections can be identified on cytology.
Overall, a combination of a thorough physical exam, eye stains, cultures, cytology, and potential biopsies allow vets to determine the underlying cause of eye discharge.
Treatment
The main treatments for conjunctivitis in cats are antibiotics, antivirals, anti-inflammatories, and eye drops. Vets typically prescribe antibiotic eye drops or ointment to be applied multiple times per day for 2-3 weeks. Common antibiotics used include neomycin, polymyxin B, bacitracin, and gentamicin.[1] If the conjunctivitis is caused by a virus, antiviral eye drops may be prescribed, such as idoxuridine or cidofovir.[2]
Anti-inflammatory eye drops can help reduce swelling, redness, and irritation caused by conjunctivitis. These may contain medications like prednisolone or dexamethasone. Keeping the eyes lubricated with artificial tear eye drops may also provide relief. It’s important to follow your vet’s instructions carefully and finish the full course of treatment, even if your cat’s eyes look better.[3] This helps ensure the infection is fully resolved.
Prevention
There are several ways to help prevent conjunctivitis in cats:
Maintain good hygiene around your cat. Wash your hands before and after touching your cat’s eyes or face. Disinfect toys, food bowls, litter boxes, and other items regularly. This helps reduce exposure to bacteria, viruses, and irritants that can cause conjunctivitis (Source 1).
Vaccinate your cat against common infectious causes like herpesvirus, calicivirus, and chlamydia. Follow your veterinarian’s recommended vaccine schedule to provide immunity against these diseases (Source 2).
Reduce exposure to irritants like cigarette smoke, dust, and chemicals in the home. Cats with allergies are prone to conjunctivitis flare-ups when exposed to irritants. Keeping their environment clean and allergen-free can help (Source 3).
