A "cataract" is any opacity of the lens of the eye, which impacts the ability of the lens to absorb light and therefore adversely affects vision. Cats of either gender can develop cataracts, and certain breeds are especially at risk. Cataracts are more common in older animals but can be present at birth or develop very early in life. Cats have cataracts much less frequently than dogs.
How Cataracts Affect Cats
Regardless of the cause of cataracts, the clinical signs are the same. Cats with cataracts have cloudy pupils (or icy-blue "chips" in the pupils), and have impaired vision in one or both eyes, ranging from mild sight problems to complete blindness. Cataracts can appear suddenly or slowly. Some of the signs associated with impaired eyesight include abnormal ambulation, unsure footing, tripping over or bumping into objects, walking into walls, misjudging distances and not recognizing familiar people. Cataracts are normally painless, but they can cause painful and permanent eye damage if left untreated. Cats can develop a condition called nuclear sclerosis which also causes a cloudy appearance on the lens of the eye. Many owners confuse this condition with cataracts, but unlike cataracts nuclear sclerosis does not impair a cat's vision.
Causes of Cataracts in Cats
Cataracts typically have a strong genetic component. Other contributing causes in cats include nutritional deficiencies, low blood calcium levels, exposure to toxins, radiation, electric shock and blunt or penetrating trauma. Cataracts can occur spontaneously and tend to become more common with increasing age.
Preventing Cataracts in Cats
The only way to reduce the prevalence of cataracts is to remove affected and carrier animals from the breeding population. Even this will not guarantee that future generations will be free of the condition.
While cataracts almost always affect a cat's vision, they do not affect its overall health. Most cats adjust to their vision deficiencies extremely well even without treatment. However, surgical treatment for cataracts is highly successful, and the prognosis for cats with cataracts is excellent if they are identified and treated early, and of course kept inside for their safety and well-being.
The term "cataract" refers to any opacity, regardless of size, of the lens of the eye. Cats of either gender can develop cataracts for a number of different reasons, although in cats most reported cases have been congenital. Certain breeds appear predisposed to developing cataracts, including Persians, Birmans, Himalayans and Domestic Shorthairs. Regardless of the cause of cataracts, the clinical signs are the same.
Symptoms of Cataracts in Cats
The chief complaints by owners of cat with cataracts are cloudy pupils (or cloudy spots in the pupils) and impaired vision. Cataracts can occur in one eye or in both. They can appear suddenly or they can develop over a period of years. In cats, cataracts often are present at birth. The cloudy lens can look "crackled," but in cats more commonly looks like an icy-blue chip of ice. The cataract may cover the entire pupil, or only part of it. Depending on the severity of the cataract, affected cats will display a range of vision problems from mild impairment to complete blindness. Some of the signs associated with impaired vision include a high-stepped walk, unsure footing, tripping over or bumping into objects, walking into walls, misjudging distances and not recognizing familiar people. However, many cats do not show any clinical signs of decreased vision, especially if only one eye is affected. Cataracts are normally painless but can cause inflammation and result in permanent eye damage.
When feline cataracts are caused by an underlying medical condition, additional clinical signs may occur. Uveitis is an inflammatory ocular condition that commonly is caused by an immune system abnormality. Uveitis can contribute to the development of cataracts. Symptoms of uveitis include squinting, watery eyes, changes in eye color, abnormal pupil size or shape and lens cloudiness.
Prompt medical treatment for any eye disorder is essential to preserve the cat's vision and relieve pain.
There are a number of diagnostic tests that can be conducted to confirm whether a cat has cataracts and, if so, to determine the cause of the condition.
Diagnosing Feline Cataracts
At the outset, your veterinarian will observe and assess your cat for any obvious signs of vision difficulty. The initial work-up will include evaluation of pupil size and symmetry and assessment of pupillary light reflexes. The veterinarian will check the "menace reflex" by moving one hand swiftly toward the cat's face, then stopping abruptly. Another test frequently done to detect vision deficiencies is to throw a cotton ball onto the floor while watching to see if the cat follows the movement.
The intraocular pressure of the cat's eyes will be assessed to rule out glaucoma. The veterinarian tests the pressure inside the eye using an instrument called a "tonometer." Assuming that intraocular pressure is normal, the veterinarian normally will dilate the cat's pupils and use a penlight or other light source to characterize the nature and extent of the cataract and to evaluate for possible concurrent uveitis. Anesthetic drops are normally applied to the eyes before these tests occur to ensure a painless examination and accurate test results.
Other tests that veterinarians commonly use to diagnose eye conditions include the Schirmer tear test and staining the eye with a fluorescein dye. These two tests are used to assess the moisture level of the eye, look for possible foreign bodies and determine whether the cornea has been damaged. Ocular ultrasonography and electroretinography are available for advanced evaluation of the retina and other eye structures. These advanced diagnostic tests are normally performed if surgery is anticipated.
Once cataracts are definitively diagnosed, blood tests typically will be recommended to rule in or out any underlying medical conditions that may have contributed to their development. A complete blood panel can identify many underlying medical conditions if present, and specialized blood tests can identify specific diseases such as feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP) and the feline leukemia virus (FeLV).
If you notice any change in your cat's eyes, schedule an appointment with your veterinarian. Many eye disorders worsen progressively if not treated in a timely manner. Prompt diagnosis and treatment can help preserve a cat's vision and relieve pain.
Obviously, owners should seek veterinary advice if they suspect that their cat has cataracts. Cats with concurrent uveitis (inflammation of certain interior structures of the eye) can be treated with topical anti-inflammatory medications. However, there is no medical treatment to eliminate cataracts. The only way to "cure" cataracts is to remove them surgically. Short of blindness, cataracts can develop into glaucoma and retinal detachment, at which point surgery may no longer be a viable treatment option. Many owners decide not to treat cataracts because cats commonly adjust quite well to vision impairment.
Treating Cataracts in Cats
Cataracts in very young kittens sometimes spontaneously improve and may not require treatment. Cataracts that have just occurred and have very low opacity (classified as immature, incipient, non-progressive or incomplete) may also require no treatment, other than possibly topical anti-inflammatory eye drops. Cataracts caused by nutritional deficiencies cannot always be treated with supplements, but their progression may be slowed or stopped with appropriate dietary supplementation, which your veterinarian can discuss with you.
The only truly effective treatment for cats with impaired vision due to cataracts is surgical removal of the affected lens. There are several surgical procedures that can be considered, and this surgery is normally performed by a specialized veterinary ophthalmologist. The goals of surgery are to restore the cat's vision and hopefully prevent the common secondary sequellae of cataracts: uveitis, glaucoma and retinal detachment. The prognosis for surgery is better if it is done early in the course of cataract development. Of course, a veterinarian will want to be sure that the cat is otherwise systemically stable and healthy prior to surgery.
Cataract surgery requires preliminary ophthalmic ultrasound and an electroretinogram to determine whether the posterior part of the eye is normal. If it is, the veterinary ophthalmologist typically will remove the cataract through a procedure called phacoemulsification, which involves ultrasonic fragmentation of the lens itself. This is followed by implantation of an artificial lens to restore the cat's normal vision. Without this artificial lens, cats will be extremely far-sighted after cataract surgery, with little useful remaining vision. If cataract surgery is not performed, the cataracts should be monitored frequently for progression. If the condition causes total or near-total vision loss (often with accompanying pain), surgical removal of the eye (enucleation) may be advised. Cataract surgery is expensive, and many owners decide that it is unnecessary due to their cat's ability to acclimate to their environment even with incomplete, or possibly total, vision loss. Cats use their sense of smell for the majority of their navigation skills and actually do not have very good vision to begin with. Cats with decreased or total loss of vision should be kept indoors at all times for their safety and well-being.