The lens is transparent crystalline structure encased in a capsule which sits behind the iris (the coloured part of the eye), its role is to focus light onto the retina. A cataract is a clouding/opacity of the lens in the eye, resulting in impaired vision and eventually blindness. They are less common in cats than dogs.
Cataracts occur for a range of reasons, including the natural ageing process, trauma, inflammation, anterior uveitis, hypertension, metabolic disorders (such as diabetes, hypocalcemia, and hypoparathyroidism), poor nutrition and drugs (particularly antibiotics) or toxins.
Either part of, or the entire lens can be affected, they can be unilateral (one eye), or bilateral (both eyes). Obviously, the larger the area affected, the greater the effect on your cat's vision.
Cataracts are classified according to your cat's age and the size of the cataract. While extremely rare, cataracts can be present at birth (congenital) or occur in young cats. When they are found in young to middle-aged cats they are known as "juvenile cataracts", and "senile cataracts" in older cats. Cataracts can progress, over months or years or quickly, over days, depending on the cause.
Cataracts are classified as:
Very small - Incipient (immature) cataract.
Small - Immature cataract.
Large (filling the entire lens) - Senior cataract.
What are the symptoms of cataracts in cats?
Symptoms may vary depending on the underlying cause. For example, if diabetes is responsible, your cat may be drinking and urinating more often. You may not notice your cat has a cataract until it is quite large and/or signs of poor vision become apparent such as bumping into walls, reluctance to climb stairs etc.
If you look carefully into your cat's eye(s), you may notice a blue/grey cloudy appearance in the pupils of the eye.
How are cataracts diagnosed?
Another condition known as "nuclear sclerosis" also resembles cataracts and your veterinarian will need to distinguish this from the cataract. Nuclear sclerosis occurs as the lens loses water due to ageing, resulting in the formation of a blue haze. This does not impede vision and requires no treatment.
Some veterinarians will refer your cat to a veterinary ophthalmologist (eye specialist). During the examination, your veterinarian will carefully check the eyes using an ophthalmoscope, and obtain a medical history from you. He may notice blue/grey spots in the eyes. Diagnostic tests will be required to determine the underlying cause (if any), and prior to any surgery, they may include:
Complete blood count to check for infection or inflammation.
Biochemical profile to evaluate how the organs are functioning.
Ultrasound of the eye may be necessary if the cataract is too cloudy to examine the retina.
Slit lamp examination involves the use of a special "slit lamp" to see the front of the eye under magnification.
Electroretinogram (ERG) is a test which measures the electrical activity of the retina which helps to assess retinal function. Cataract surgery is not recommended if the retina is not working properly.
How are cataracts treated in cats?
Addressing the underlying cause, if one is determined.
Incipient cataracts may require close monitoring only to ensure they don't grow in size, inhibiting vision.
Surgery involves removal of the lens. Ultrasonic waves are used to liquefy the lens, which is then aspirated (sucked out). This treatment is known as "phacoemulsification". In some (not all) cases, an artificial lens will then be inserted. This is the most common method of removal.
Another method is extracapsular lens extraction, which involves removing the lens as a whole. This is indicated where the necessary equipment for phacoemulsification isn't available or if the lens is too solid to be broken up.
In some cases, your cat may not be a suitable candidate for surgery. Anti-inflammatory and/or antibiotic drops may be recommended to treat inflammation.
Image courtesy of Helen Haden.