If your agile cat suddenly becomes clumsy, or your affectionate cat now flinches when you reach over his head to pet him, his vision may be cloudy because he has cataracts in one or both eyes.
Cataracts are opacities that develop within the normally clears lens, the structure inside the eye that is responsible for focusing. Cataracts block light from being focused on the retina, the membrane at the back of the eye whose tiny cells are responsible for generating images. In cats with cataracts, a haziness or cloudiness of the lens may be evident in the later stages of the condition.
Unobvious Signs. The incidence of cataracts is relatively low in cats — and they might not be apparent to owners — but left untreated over time, cataracts can cause blindness, says Seth Eaton, VMD, ACVO, former Staff Ophthalmologist at Cornell University Veterinary Specialists in Stamford, Conn. Cataracts can also lead to uveitis, an inflammation inside the eye, and glaucoma, a painful disease associated with elevated pressure inside the eye that can result in blindness.
Though inherited cataracts are uncommon in cats, breeds with an increased risk include Birmans, Persians and Siamese. “However, cataracts can develop in any cat at any age, and they can progress slowly or come on very quickly,” says Dr. Eaton. “A cloudy spot grows inside one or both lenses, and at the microscopic level, the normally clear proteins in the lens are undergoing a progressive change that can eventually cause blindness.”
While factors like aging can contribute to the development of cataracts in senior or geriatric cats, the most likely cause of cataracts in cats after aging is uveitis or inflammation inside the eye.
“There is a laundry list of infectious diseases that cats can get — feline leukemia, feline infectious peritonitis, feline immunodeficiency virus, as well as fungal and bacterial infections that can potentially induce uveitis in the eye,” says Dr. Eaton. “Uveitis can also be caused by a blunt or sharp trauma to the eye that can alter the delicate environment of the lens and lead to cataract formation.”
Other causes of feline cataracts include poor nutrition as a kitten, injury, inflammation, exposure to toxic substances, radiation and electric shock. Sometimes, the reason is simply unknown.
Because cats may mask outward signs of discomfort or pain, Dr. Eaton urges owners to be alert for these subtle behavioral changes:
– Bumping into furniture, such as the recliner or sofa that has not been recently moved.
– Miscalculating the distance from the floor to a favorite catnapping spot, such as the top of the sofa or sturdy shelf.
– Hesitating to use stairs, especially when descending.
– Forgetting the location of food and water bowls and litter boxes.
– Changing elimination and litter box habits.
“Cataracts may not cause any detectable visual impairment signs that are obvious to pet owners until advanced stages,” says Dr. Eaton. “That’s why we highly recommend that pets receive thorough physical examinations at least once a year and that those exams include assessing the health condition of the eyes.”
During an eye exam, a veterinarian may use an ophthalmoscope (a light-affixed magnifying glass) to study all parts of the eyes’ structure and health. It’s common for a veterinarian to turn off the lights and use the scope to conduct an evaluation without the glare from room lighting. “Evaluations of the structures of the eye are best performed in a dimly lit room,” Dr. Eaton says.
The Examination. Various types of eye drops may be used during the examination, depending on the cat’s age and health. To test eye pressure, the veterinarian applies a drop of topical anesthetic to numb the eyes’ surface. A green dye called fluorescent stain may be used to identify ulcerations of the cornea, and another drop may be applied to dilate the pupils. “This drop opens the pupil further to allow the veterinarian to look deep into the eye to evaluate the entirety of the lens and all the way back to the retina to make sure it is healthy,” Dr. Eaton says.
If tests confirm the presence of cataracts, the most effective treatment is surgery. The best candidates are in good health with no evidence of any inflammatory conditions. “There should be no detection of inflammation in the eyes because the eye needs to be at a quiet state during surgery,” Dr. Eaton says. “And any eye with uveitis will be more prone to inflammation internally after surgery.”
In the surgical procedure called phacoemulsification, the affected lens is removed, similar to procedures in people, and an artificial lens may be implanted. The procedures, which are performed under general anesthesia, generally take 45 minutes to one hour per eye.
In some instances, veterinarians remove the cataract, and the lens remains, causing blurry vision because the cat becomes farsighted, unable to see as well at a distance. Veterinarians will examine the cat’s eyes in post-surgical visits and commonly prescribe antibiotics and anti-inflammatory medications. They will conduct additional tests to make sure the retina is healthy and functioning properly.
The rate of surgical success in cats has not been determined, so each cat’s candidacy must be considered individually. Immediately after surgery, patients are fitted with a special collar to prevent clawing or rubbing of the eye. Ideally, the collar should be clear rather than tinted so the cat can better see
his surroundings.
If your cat isn’t a good candidate for surgery, the usual plan calls for more regular veterinary examinations, with assessments once or twice a year by an ophthalmologist to detect the cataract’s progress and presence of any other ocular condition. “Cataracts, over time, become denser and that can lead to sudden inflammation in the eye and induce further uveitis in the eye that will need prompt treatment,” Dr. Eaton says. “We also want to keep tabs on the eye for any elevated pressure (glaucoma) that can cause pain to the cat.”
No medication is available to treat or prevent cataracts in cats. Over-the-counter nutritional supplements and topical eye drops will not cure cataracts, Dr. Eaton says. “We would love to have a topical medication available, but there has been no good scientific evidence to prove these products will prevent or reverse cataracts.”
In the end, you can play a pivotal role in the short and long-term health of your cat’s eyes by examining his eyes monthly and reporting any changes in them or in his behavior to his veterinarian. And be sure to include an ocular exam as part of your cat’s annual or semi-annual veterinary exam. ❖
Why Diabetes Isn’t a Common Factor
Diabetes is not a common cause of cataracts in cats, as it is in dogs, says ophthalmologist Seth Eaton, VMD. One reason: An enzyme known as aldose reductase. Diabetes causes high glucose levels in the blood, and when it gets into the lens in excessive amounts, it can’t be metabolized efficiently.
“The activity of this enzyme leads to ‘trapping’ of the sugar in the lens, causing fluid buildup and protein changes that lead to cataracts in dogs,” says Dr. Eaton. “It’s a completely different story in cats. We know that the aldose reductase inhibitor enzyme inside the lenses of adult cats is not as abundant as it is in adult dogs. It’s a protective feature of cats that doesn’t allow this enzyme to alter the sugar in the eyes as it does in dogs. So unless there is a development of diabetes in a young cat, diabetic-induced cataracts are rare.”
NOT TO BE CONFUSED WITH CATARACTS
If the lenses of your older cat’s eyes have taken on a smoky blue appearance, it’s not necessarily a sign of cataracts. It may be nuclear sclerosis, a natural age-related hardening of the lens that doesn’t require surgery. The condition requires no treatment and usually does not impair vision.
