The first clue to vision loss in your cat is usually a behavior change. She may move more cautiously, possibly bump into things. She may no longer jump onto favorite perches, and she may not think “chase the feather” games are as fun as they used to be. Although you should always watch for changes in your cat’s eyes—redness, cloudiness, squinting, or unusual pupil responses—these symptoms aren’t always easy to see.
Healthy feline eyes are bright and clear, the pupils are of equal size, and the cat should not squint with either eye. There should be little or no tearing in the corners of the eye, and the tissue lining the eyelid should be a healthy pink.
Loss of vision may be due to an injury, genetics, or disease. Cataracts, glaucoma, and retinal detachments are causes that can result in anything from a minor inconvenience to total blindness. Vision loss is usually gradual in middle-aged and older cats, but sudden vision loss may occur with retinal detachment.
The retina is the layer of pigmented cells coating the back of the eye. These cells receive light (images) from the front of the eye and transmit them to the brain. If the retina detaches, that area will no longer transmit visual images.
Retinal detachment tends to be a disease seen in elderly cats. It often occurs secondary to hypertension caused by either renal disease or hyperthyroidism. Trauma and any cause of bleeding in that area of the eye may damage the retina. If there is trauma or bleeding into the eye, you may notice this, but cats will often present with acute onset of blindness.
Diagnosis requires a thorough ophthalmic examination. In some cases, ocular ultrasound may be required if corneal opacity or cataracts prevent the veterinarian from evaluating the retina (more on cataracts coming up). Your veterinarian will evaluate the whole cat, not just her eyes.
For instance, hypertension could indicate kidney problems or hyperthyroidism. Normal systolic blood pressure for an adult cat is between 100 and 160 mmHg. Any cat with a reading higher than 170 mmHG is considered to have high blood pressure. (Note, this should be checked more than once, as a stressed cat may have a false high reading.)
If the detachment and hypertension are diagnosed within 24 hours, reattachment of the retina may be possible with appropriate therapy for hypertension. Kidney failure and hyperthyroidism require additional diagnostics and medications. Surgical repair can sometimes partially restore vision, but the prognosis is guarded with a retinal tear or detachment.
While not as common in cats as in dogs, cataracts can occur in one or both eyes. Some cataracts are minor and merely cause a small area of vision loss. Mature cataracts may cause total loss of vision.
A cataract is an opacification (clouding) of the lens of the eye. The lens is normally a transparent structure that focuses light coming into the pupil onto the retina at the back of the eye. If the lens becomes cloudy, it can block light from getting back to the retina.
Cataracts may be caused by a variety of things, including diabetes, aging, electric shock, a perforated lens, inflammation in the eye, certain medications, toxins, or poor nutrition.
Uveitis (inflammation of the pigmented portions of the eye) is the most common cause of cataracts, and this may occur secondary to systemic illnesses, including feline leukemia, feline immunodeficiency virus, feline infectious peritonitis, and feline herpesvirus-1. In addition to causing cataracts, these illnesses may lead to luxation of the lens. Usually, however, the actual cause is never identified.
Incipient cataracts are small areas of lens involvement that have a minor effect on vision. Immature cataracts have not reached full density, so they still allow light to pass through. Mature cataracts are solid and usually cause blindness.
A study published in Veterinary Ophthalmology looked at 2,000 normal cats and found that by 12 to 14 years of age, about half of cats had some type of cataract. By 15 to 20 years of age, virtually all the cats examined had cataracts. Luckily, these cataracts tended to be small or not fully mature so the cats retained some vision.
Himalayan, Birman, Persian, Bengal, Russian Blue, and British Shorthair cats have a congenital predisposition to cataracts. These cats can present with cataracts as young as 2 to 5 years of age. Some are small cataracts that don’t progress to full size and, although they do limit vision, they don’t cause total blindness for the cat.
Surgery by a board-certified veterinary ophthalmologist is the only real treatment for cataracts. The cataracts can be removed through a process called phacoemulsification, which destroys the defective lens, or the lens may be extracted whole. An artificial lens can be placed to restore vision. Surgery is usually only pursued if a cat has cataracts in both eyes and has total vision loss.
Surgery is not recommended if your cat also has recurrent uveitis, retinal damage, or glaucoma.
Signs of glaucoma, or elevated pressure within the eye, in a cat can be quite subtle, says Thomas Kern, DVM, DACVO, Associate Professor in the Section of Ophthalmology at Cornell. Owners may notice the eye(s) becoming cloudy and one eye may enlarge compared to the other. They may notice their cat squint or that the pupil of the affected eye may not react normally to light changes.
“Typically,” he adds, “the progression takes months or longer before changes are noticed. Even with significant eye discomfort, a cat with visual impairment can continue its normal indoor and outdoor activities.” This means that owners must be very observant.
Glaucoma can lead to total vision loss and is usually secondary, which means it is the result of a process other that a structural defect in the eye itself. Primary glaucoma is quite rare, and often results from a structural genetic defect that prevents fluid outflow from the inside of the eye. Burmese and Siamese cats are genetically predisposed to glaucoma.
Diabetes and Cataracts
Uveitis is a major cause of secondary glaucoma. With uveitis, inflammatory cells can build up inside the eye and block its outflow tracts. Toxoplasmosis can be a source of uveitis. Hemorrhage into the eye, possibly from systemic hypertension, may cause a similar cellular blockage of the draining tracts of the eye. Cancers such as iris melanoma or lymphoma may also contribute to glaucoma.
In a normal eye, the aqueous humor (liquid in the chamber between the cornea and the lens) is continually produced and drained. With glaucoma, the fluid can’t drain appropriately, leading to increased intraocular pressure (IOP) and compression of the optic nerve. Ultimately, the compressed optic nerve loses its ability to transmit data to the brain, leading to vision loss. Elevated IOP is the hallmark of glaucoma.
The tonometer used to measure your cat’s IOP is not painful, and cats are checked while awake (a topical anesthetic is often applied to the cat’s eyes). Both eyes should have similar readings. Since glaucoma can, and often does, first appear in one eye, a dissimilar reading is cause for concern. A through ophthalmic examination is essential to obtain an accurate diagnosis.
With nuclear lenticular sclerosis (NLS), an age-related change seen in most cats over 8 years old, a hazy discoloration of the eye may be noted. As it progresses, the lens loses flexibility, but the cats retain vision. NLS is usually in both eyes.
Glaucoma is not as common in cats as in dogs and tends to occur more gradually than in dogs. With gradual progression, many cats simply adapt to the increasing loss of vision. Unfortunately, this often means that by the time glaucoma is diagnosed in cats, irreparable damage may already be done.
The first step in treatment is to determine the cause of the increased IOP. If uveitis is suspected, treatment of this inflammatory process is usually the first step. Other helpful medications may include carbonic anhydrase inhibitors and/or beta blockers (both of which lower aqueous humor production). Some drugs act by both reducing fluid production and increasing fluid outflow.
Medical treatment of glaucoma usually requires multiple daily administrations of topical drops, which can be difficult for some owners.
For cats that have gone blind from glaucoma, the best solution may be to remove the eye. While this may seem dramatic, it removes the source of pain, and most cats adapt quite well once recovered.
What You Should Know
Symptoms that may be associated with visual impairment
- Bumping into furniture or tripping on stairs
- Difficulty finding litterbox or food/water bowls
- Behavior changes
- Squinting, redness, drainage
- Color changes in the iris
- Cloudy eyes
- Protruding third eyelid
- Pupils differ from one another