Eyes are very important sensory organs to a cat. Being sure that your cat’s eyes are healthy should be a part of an annual comprehensive physical examination by your veterinarian. I have diagnosed different diseases of the eyes and even blindness when cats have been brought in for routine visits, because owners often just don’t realize a problem exists.
An examination of the eyes starts with inspection of the eyelids and skin around the eyes. Any discharge, inflammation, or hair loss should be noted. Next the surface of the cornea is examined. Any cloudiness, redness, or imperfections are noted. If the cornea seems dry, or if a lack of tear production is suspected, a Shirmer tear test can be performed. This test utilizes a small piece of filter paper that absorbs tear fluid over a 60-second period of time. Normal cats will produce over 15 mm of tears in each eye during this time.
The cornea can then be checked for surface irregularities such as a scratch or ulcer. This is performed by placing a drop of a fluorescent dye on the corneal surface, then rinsing it off. The normal cornea is smooth, and the dye rinses off. Any irregularities will trap the dye on the cornea and this can be seen with a black light or sometimes even with room light.
If cat is squinting, another procedure that should be performed is examination of the inside of the eyelids. Most cats do not allow a veterinarian to probe under the lids unless a topical anesthetic is first applied to them. Sometimes sedation or anesthesia is needed. A special round-ended probe, called a Strabismus hook, is used to check under the lids. Foreign objects such as foxtails or litter can be found this way.
An instrument called an ophthalmoscope can be used to examine the tissues behind the cornea. The retina and optic disc (area where the optic nerve leaves the retina) can be visualized by the veterinarian. The reflective tapetum can be examined this way as well.
If the eye is bulging or if glaucoma is suspected, measurement of eye pressure can be taken with an instrument called a tonometer. Glaucoma is found in cats, but it is not as common as in man or dogs.
There are veterinarians who are board certified in ophthalmology. These doctors will be able to perform even more specialized tests of the eye using different types of lenses and lights. They can perform electroretinography (ERG) that can measure total electrical activity of the eye when stimulated with light. This test is used to measure retinal function. It is useful as a pre-surgical test for cataract or glaucoma procedures, or to assess how an eye has been affected by trauma.
Veterinary ophthalmologists perform all types of high tech eye surgery including replacing lenses, grafting corneas, and placing prosthetic eyes in animals that have lost an eye. Most veterinary practitioners refer to an ophthalmology specialist when disease affecting the eye is complicated.
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. Retinal detachment can occur with hypertension and blindness follows. Controlling the blood pressure can potentially restore vision.
The most common problem directly affecting the eyes of cats is conjunctivitis. People like to call conjunctivitis “pink eye”, and conjunctivitis is a non-specific term describing inflammation of the conjunctiva. 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. Owners should suspect conjunctivitis if their cat’s eye tears excessively or looks red or puffy. It can be difficult for a veterinarian to determine an exact cause of a case of conjunctivitis. Cultures and conjunctival scrapings are not routinely reliable diagnostic tools. 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’s eyes is recommended.
Kittens that suffer from severe conjunctivitis often have other upper respiratory infection signs such as sneezing and congestion. Scarring of the nasal lacrimal duct, the outflow tract of tears from the eye, can result from these infections. This can lead to lifelong tearing of the eyes.
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. We carry a product called I’Lid N Lash that helps loosen debris and soothes the eyes. The short nosed cats may need their eyes cleaned 2-3 times daily to prevent buildup. If the discharge builds, it can cause hair loss and dermatitis in the skin folds around the 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. If your cat develops third eyelid elevation, consult your veterinarian.
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. Orange cats can develop black pigment around their eyelids, noses, and lips, which is normal, and not to be confused with skin cancer.
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