What is conjunctivitis in cats?
Conjunctivitis is inflammation of the conjunctiva, which is the thin transparent tissue that lines the inner eyelid and covers the white part of the eye 1. It is often referred to as “pink eye” due to the redness and inflammation that occurs. The conjunctiva contains a large number of small blood vessels that can become swollen, which causes the red appearance in the eye.
Common symptoms of feline conjunctivitis include:
- Redness in one or both eyes
- Discharge or mucus from the eyes
- Excessive tearing
- Squinting or spasms of the eyelids
Conjunctivitis in cats is similar to what humans call “pink eye” – the inflammation that causes the vessels in the eye to become swollen and appear pinkish-red. However, the underlying causes of feline conjunctivitis tend to differ from the common causes of pink eye in humans.
Causes of feline conjunctivitis
There are several potential causes of conjunctivitis in cats:
Viral causes
Viral infections are a very common cause of feline conjunctivitis. The most common viruses are feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV). FHV-1 is the most prevalent cause of viral conjunctivitis in cats. It infects the cornea and conjunctiva. Symptoms include watery eyes, squinting, redness, and ulcers on the cornea. FHV-1 infection can become chronic and recur throughout a cat’s lifetime during periods of stress https://vcahospitals.com/know-your-pet/conjunctivitis-in-cats.
Bacterial causes
Bacterial infections are another common cause of infectious feline conjunctivitis. The most common bacteria are Chlamydophila felis and Mycoplasma felis. These bacteria can cause inflammation of the conjunctiva and lead to ocular discharge, redness, and squinting. In some cases, they may also infect the cornea. Chlamydophila and Mycoplasma bacteria often occur as secondary infections along with viral causes of conjunctivitis https://bondvet.com/b/conjunctivitis-in-cats.
Allergies
Allergies can also be an underlying cause of conjunctivitis in cats. Allergic reactions cause inflammation of the conjunctiva and discharge from the eyes. Pollens, chemicals, smoke, dust mites, and other irritants may trigger allergic conjunctivitis. Seasonal allergies often cause conjunctivitis outbreaks in the spring and summer https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/conjunctivitis.
Irritants
Foreign materials, chemicals, or other irritants may also directly irritate a cat’s eyes and cause conjunctivitis. Dust, smoke, shampoo, debris, and substances that a cat’s paw may pick up can all irritate the conjunctiva. In some cases, ingrown eyelashes or eyelids turned inward may physically irritate the eye. Identifying and removing irritants is an important part of treating conjunctivitis.
Viral conjunctivitis
Viral infections are the most common cause of conjunctivitis in cats. The two main viruses that cause conjunctivitis in cats are feline herpesvirus (FHV-1) and feline calicivirus (FCV).
Feline herpesvirus is the leading cause of viral conjunctivitis in cats. It is extremely contagious and spreads through direct contact and respiratory secretions. Once a cat is infected with FHV-1, the virus remains latent for life and can reactivate during times of stress. Recurrent ocular manifestations are common with feline herpesvirus infection [1]. Symptoms of herpetic conjunctivitis include ocular discharge, conjunctival hyperemia, chemosis, corneal ulcers, and blepharospasm.
Feline calicivirus is another common viral pathogen implicated in feline conjunctivitis. It generally causes a milder conjunctivitis compared to FHV-1. Symptoms include conjunctival hyperemia, ocular discharge, and ulcers on the tongue, hard palate, and nose [2].
Bacterial conjunctivitis
Some common bacterial causes of conjunctivitis in cats include Chlamydia felis and Mycoplasma species. Bacterial conjunctivitis is highly contagious and can spread through direct contact with eye discharge from an infected cat.
Symptoms of bacterial conjunctivitis include redness, swelling and discharge from the eyes. There may be excessive tearing and blinking. Some cats may have crusty deposits in the corners of their eyes. Unlike viral conjunctivitis, bacterial conjunctivitis often affects both eyes.
Allergic conjunctivitis
Allergic conjunctivitis occurs when a cat’s immune system overreacts to normally harmless substances like pollen, dander, mold, or dust. These allergens trigger the release of chemicals like histamine that cause inflammation and irritation of the conjunctiva (the thin membrane covering the eye).
Common allergens for cats include:
- Pollen – From trees, grasses, and weeds
- Dust mites
- Animal dander – Especially cat dander from grooming
- Mold spores
- Household cleaners or cigarette smoke
Symptoms of allergic conjunctivitis include:
- Redness and swelling of the conjunctiva
- Excessive tearing
- Thick yellow or green eye discharge
- Itching, burning, or irritation of the eyes
- Squinting or blinking more than normal
- Rubbing or pawing at the eyes
The symptoms may affect one or both eyes, and tend to come and go with exposure to the allergen. Cats may also have additional allergy symptoms like sneezing, coughing, or skin irritation.
Other irritants
Irritants like dust, chemicals, and smoke can also lead to conjunctivitis in cats. These airborne particles can cause inflammation when they come into contact with a cat’s eyes. Sources of irritants include:
- Dust – Dust particles from carpets, bedding, and furniture can irritate a cat’s eyes. Cats with recurring dust allergies may rub their eyes frequently.
- Chemicals – Exposure to chemicals like household cleaners, cigarette smoke, perfumes, etc. can trigger conjunctivitis. Chemical fumes directly irritate the ocular membranes.
- Smoke – Smoke from cigarettes, fires, vehicles, etc. contains tiny particles that can get lodged in the eyes. This causes redness, swelling, and discharge.
Common symptoms from irritant exposure include redness, swelling, increased tear production, and green/yellow discharge. Cats may squint or keep their eyes closed if bright light hurts their eyes. Recurrent exposure can lead to chronic irritation and infection.
Diagnosing conjunctivitis
To diagnose conjunctivitis, your veterinarian will perform a thorough eye exam to check for symptoms like swelling, redness, and discharge. They will look for foreign bodies, ulcers or other irritants on the eye’s surface. Fluorescein dye may be applied to check for scratches on the cornea (VCA).
Other diagnostic tests may include:
- Schirmer tear test to measure tear production
- Tonometry to check eye pressure
- Cytology to look at cells under a microscope
- Bacterial culture to identify infection
- PCR testing for viral infections like feline herpesvirus (Cornell)
Your vet will perform a full exam to pinpoint the cause of conjunctivitis and recommend appropriate treatment.
Treatment
Treatment for feline conjunctivitis depends on the underlying cause. Viral and bacterial conjunctivitis are often treated with medication, while allergic conjunctivitis may require managing environmental allergens.
For viral conjunctivitis, antiviral medication may be prescribed, such as idoxuridine 0.1% or cidofovir 0.2% eye drops (https://www.medvet.com/conjunctivitis-in-cats/). These antiviral medications can help resolve symptoms and shorten the course of viral conjunctivitis.
Bacterial conjunctivitis is treated with antibiotic eye drops or ointment, such as gentamicin, chloramphenicol, or ciprofloxacin. These are applied to the eye several times per day for 7-14 days (https://vcahospitals.com/know-your-pet/conjunctivitis-in-cats). Antibiotics help eliminate the bacterial infection causing the conjunctivitis.
Anti-inflammatory eye drops containing corticosteroids may also be prescribed for bacterial, viral, or allergic conjunctivitis. These help reduce inflammation and irritation of the eye (https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/conjunctivitis).
For allergic conjunctivitis, treatment focuses on managing the underlying allergy. This may include avoiding exposure to environmental allergens, antihistamines, or immunotherapy. Corticosteroid eye drops can also help control inflammation from allergic reactions.
Home care
There are some things you can do at home to help care for a cat with conjunctivitis and support their recovery:
Cleaning the eyes is important to help flush out discharge and prevent further irritation. Use a clean, soft cloth dampened with warm water to gently wipe away any crusty discharge from around the eyes. Avoid rubbing too hard. You can also use sterile saline eye drops or washes to help rinse the eye. Just pull down the lower eyelid and apply a drop or two of the cleaner (source).
Try to reduce your cat’s exposure to potential irritants during an infection. This may mean keeping them indoors, avoiding cigarette smoke, and using unscented litter. Don’t allow other pets to get too close either.
Follow up with your vet as recommended for rechecks and to monitor how the infection is responding to treatment. You may need to get prescription antibiotic eye drops or ointments to properly clear up bacterial conjunctivitis.
Prevention
There are several ways to help prevent conjunctivitis in cats:
Vaccination – Vaccinating cats against common viruses like feline herpesvirus and calicivirus can help reduce the risk of viral conjunctivitis. The feline viral rhinotracheitis vaccine provides protection against herpesvirus and calicivirus (PetMD).
Reducing exposure to infections – Keeping cats indoors and away from other cats can limit exposure to contagious conjunctivitis viruses and bacteria. Proper hygiene like washing hands after touching infected cats can also reduce spread (VCA Hospitals).
Avoiding allergens – Figuring out and eliminating environmental allergens that trigger allergic conjunctivitis can prevent flare ups. This may involve keeping cats indoors, using air filters, washing bedding regularly, and using hypoallergenic litters (MedVet).