This is part two in a two-part series on understanding the cat’s eye.
The eyes can be a window to internal problems a cat is experiencing. An example of this would be an examination of the scleral portion of the eye. If an animal is jaundiced, this normally white tissue can look yellow, and liver disease can be suspected. Another example would be the sudden onset of blindness caused by high blood pressure.
The most common problem directly affecting the eyes of cats is conjunctivitis. People like to call conjunctivitis “pink eye.” Inflammation can result from viral or bacterial infection, allergies, trauma, and immune related diseases. Conjunctivitis does not affect vision, unless the cat is holding its eye closed due to pain or discharge buildup. Most often a veterinarian will prescribe medication that will treat the clinical signs.
Kittens can be commonly infected with feline herpes virus or chlamydia that can cause conjunctivitis. Both can be difficult to treat, and the herpes can cause recurrent draining of the eye and conjunctivitis throughout the cat’s life. Feline herpes is not contagious to humans, but it is similar to the herpes simplex in humans that can cause recurrent fever blisters. Feline chlamydia can be transmitted to humans and cause conjunctivitis, so washing of the hands after touching an infected cat is recommended.
Aside from having kitten conjunctivitis, chronic tearing can occur because of facial conformation and breed predisposition. Owners of Persian and other brachycephalic breeds of cats are familiar with this. The normal drainage system for the tears does not function due to the size and shape of the eyes and nose.
A rule of thumb with regards to ocular discharge is that clear is good, and yellow or green is bad. A dark crusty material in the corners of the eyes can also be normal. Tears contain pigments that when exposed to sunlight turn dark. This is not due to blood or infection. Just like many people have “sleep” in their eyes each morning, so do many cats. Wiping with a moist tissue or cotton ball should be adequate for cleaning most cats’ eyes.
Third eyelid elevation in cats is normal during sleep, but is not normal in the awake, alert cat. Some causes of third eyelid elevation are parasites, viruses, nerve inflammation, and conformation of the lid.
Eyelid tumors are another condition worth considering in cats. White or pink skinned areas on cats are more prone to skin cancer, especially if the animal has spent a lot of time outdoors. Early signs can be recurrent crusting or scabbing of the eyelid edges.
Two eye diseases unique to cats are corneal sequestrum and eosinophilic keratitis. If you notice any type of black, red, or pink plaque of tissue on the cornea, your cat should be checked for these conditions. These conditions are treatable, but may not be curable.
There are numerous other diseases and problems that can affect all parts of the eye and its surrounding structures. Acuity of vision is not routinely measured in cats. It is normal for a cat’s lens to thicken with aging and for clarity of vision to diminish. Very few felines go blind unless another condition is present. If a cat loses vision in one eye, often an owner will not even realize it because it will still be able to function fairly normally. Even an animal blind in both eyes can get around in surroundings that it is familiar with, because it will utilize its other senses to compensate.
The eye and its connections to the nervous system are fascinating. The differences in structures, development, vision, and disease processes make the feline eye unique. Be aware of your cat’s eyes and seek veterinary care if you notice any changes.
Written by Dr. Wexler-Mitchell of The Cat Care Clinic in Orange, CA
Copyright © 2011 The Cat Care Clinic