Degeneration of the Cornea in Cats

Degeneration of the cornea is a condition that usually, but not always, occurs in only one eye and is often because of an eye disease, generalized condition, or traumatic injury. Conditions such as scars and inflammation (acute or chronic) can be associated with degeneration. It is often identified by, but not limited to, lipid (fat-soluble molecules) or calcium deposits, vascularization, or mineralization within the eye either through heredity or by way of an underlying condition.

The cornea has the same function and structure in cat eyes as in human eyes. It is a transparent lining that covers the external front of the eyeball that contains the iris, pupil, lens, retina, and optic nerve, and is continuous with the sclera, the white part of the eye. Degeneration of the cornea is not as common in cats as in dogs, but can be progressive if not treated in a timely manner. Signs of degeneration are difficult to detect due to a cat’s eye’s natural resistance to inflammation or other symptoms, which means any injury or suspected disorder of the eye needs to be treated right away before permanent damage or blindness occurs. 

Symptoms of corneal degeneration may include:

• Abnormally increased tearing or abnormally decreased tear production
• Discharge from the eye that appears clear, gray, yellow, green, or a rusty dark red color that looks like dried blood 
• Squinting
• Low blink response
• Brown or black areas on the cornea, either solid or spotted
• Swelling
• Size differences between the two eyes’ pupils
• Change in color or transparency
• Irregular border shape where the cornea blends into the sclera (the white part of the eye)
• Lesions on the eye
• Bumping into objects
• Misjudging distances

Types

Keratitis

Usually caused by the feline herpesvirus-1, inflammation can be superficial or inside the cornea (interstitial), or be due to ulcers or lesions on the cornea. Inflammation can also be due to an immune system concern. Keratitis can often be found in association with conjunctivitis, which is also caused by the feline herpesvirus-1. Each type of keratitis- ulcerative and eosinophilic- can affect any breed of cat. 

• Eosinophilic Keratitis: Lesion(s) on the eye may be evident due to an intrusion of a type of granular white blood cell called eosinophils. It is an immune system-based condition.
• Ulcerative Keratitis: Slow-healing sores may be found in or on the cornea. It is usually caused by the feline herpesvirus-1. 

It is rare for a cat with keratitis to become completely blinded. However, your cat may experience long-term pain and discomfort if the condition is not properly treated. 

Sequestration

Also called corneal mummification or corneal necrosis, this condition develops after a chronic irritation or an ulcer that will not heal. The affected area may turn light brown or black with cloudiness and can lead to pain or perhaps even corneal rupture. This is because the affected area has degenerated or contains dead tissue and blood vessels (called the sequestrum). The condition mainly affects Persian, Burmese, and Himalayan cats, but can affect any breed. It may develop as part of a secondary issue such conjunctivitis or the presence of herpesvirus infection. This condition appears to be unique to cats and can recur in the same eye or in the other eye if the cat is predisposed to it.

Several conditions can lead to degeneration of the cornea in cats:

• Corneal lacerations
• Infection from an associated condition such as an upper respiratory infection
• Feline immunodeficiency virus (FIV)
• Feline leukemia virus (FeLV)
• Feline infectious peritonitis virus (FIP)
• Feline herpesvirus (FHP)
• Feline chlamydia
• Feline mycoplasma
• Toxoplasma (parasite)
• Cryptococcus (yeast-like fungus)
• Uveitis (inflammation of the uvea)
• Melanoma
• Glaucoma
• Cataracts
• Retina detachment due to hypertension
• Hyperpigmentation
• Traumatic injury
• Excessive levels of lipids or calcium deposits in the tissue underneath the cornea (the stroma)
• Deficient phosphorus in the blood
• Excessive vitamin D
• Feeding your cat dog food, resulting in taurine deficiency

Usually, the cat’s medical history and clinical evidence is enough to make a diagnosis, though further testing is sometimes possible. 

A fluorescein stain will also be applied directly to the cat’s eye. The stain sticks wherever deterioration, a foreign object, scar, inflammation, or an ulcer may be on the cornea. A blue light shone onto the eye will reveal the issue.

If there are no apparent issues found with the fluorescein stain, the veterinarian will check for deterioration of the corneal stroma (corneal dystrophy), which is not associated with inflammation of the eye or a systemic disorder. Corneal dystrophy is not usually a progressive condition.

Your veterinarian may want to collect a sample of the conjunctiva or corneal cells for closer inspection by microscope (cytology). The discovery of white blood cells indicates that a foreign organism is present and further testing is needed. A biopsy may also be necessary in order to identify any virus or bacteria. 

Tests for underlying systemic conditions will be conducted through blood tests since corneal degeneration is mainly associated with an unknown pathogen or disease.

If feline herpesvirus-1 is the cause of the condition, or if your cat’s condition is not improving or is worsening, your veterinarian may refer you to a feline ophthalmologist.

Topical or oral antiviral medications along with an oral L-lysine supplement given for up to two weeks may be all your cat needs. With corneal sequestrum, a topical antiviral medication may be administered until the sequestrum sloughs off on its own. However, a surgical procedure called a keratectomy may be required. 

A keratectomy in cats is very similar to LASEK surgery in humans. The affected cells of the cornea are removed by use of a laser at extremely low temperatures. The procedure prevents the lesion from deepening into the eye and also provides pain relief to the cat. If the lesion has penetrated the eye too deeply, however, the affected cells will be removed and a tissue graft will be performed. The graft may be taken from the cat’s own conjunctiva or a donor cornea, or a synthetic biological or collagen disc may be utilized.

For keratitis, surgical removal of the affected area is necessary (unlike in sequestrum where it may be optional) along with topical and oral anti-inflammatory and antiviral medication. Anti-inflammatory medication will be prescribed to control the lesion. 

Additional medications may be necessary to address any underlying conditions contributing to the degeneration of the cornea. 

Surgery for cornea repair rarely has any postoperative complications. 

Proper treatment and care can prevent any recurrence or further degeneration of the cornea in a cat. There are five things you can do to help keep your cat’s eyes healthy and safe. 

Medication

Continue to give the prescribed medication for the directed time period to your cat even if it gets to be inconvenient. Following your veterinarian’s instructions is very important in restoring full health to your cat and in preventing any recurrence or complications that could lead to an even worse condition than before.

Home Monitoring

When monitoring your cat’s eye health at home, the eyes should appear bright and clear, the pupils are equal in size, and the cat is not squinting. There should be little or no tearing, the eyelid a healthy pink, and the membrane lining the inner corner of the eye not protruding. If your cat’s eye condition does not appear this way, please see your veterinarian as soon as possible. 

Regular Check-ups

Diagnosing vision trouble in cats can be difficult because of a cat’s natural ability to resist eye inflammation, so it is very important that your cat receives routine check-ups in order to detect any early signs of cornea degeneration or any other issues. The earlier a vision problem is identified and diagnosed, the more successful treatment will be. 

Minimize Stress

Keep your cat as stress-free as possible since the condition can recur because of the herpesvirus, which thrives on stress. 

Proper Nutrition

Be sure to feed your cat only commercial-grade, cat-specific food or an all-natural diet. Giving your cat a different kind of food can lead to a deficiency in dietary taurine, which your cat needs for good eye health, including proper retina attachment.