A cataract is a clouding/opacity of the lens in the eye due to proteins within the lens clumping together.
The lens is transparent crystalline structure encased in a capsule which sits behind the pupil and iris, the coloured part of the eye. The role of the lens role is to focus light onto the retina. It is predominantly made up of water and proteins in layers like an onion.
When cataracts form, the amount of light which reaches the retina is reduced which leads to blurred vision and eventually blindness. Think about how the view from a frosted window, such as a bathroom, compares to that of a clear window. It is still possible to make out shapes and shadows, but not much more.
Cataracts occur for a range of reasons which include:
- Natural aging process
- Anterior uveitis
- Electric shock
- Metabolic disorders (diabetes, hypocalcemia, and hypoparathyroidism)
- Poor nutrition during kittenhood
- Prenatal influences
- Certain drugs (antibiotics and steroids)
Cataracts can affect part of or the entire lens and can be unilateral (one eye) or bilateral (both eyes). 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 develop in young to middle-aged cats they are known as juvenile cataracts, while cataracts in older cats are known as senile cataracts. Cataracts can progress, over months or years or quickly, over days, depending on the cause.
- Incipient (immature) cataract – Very small
- Immature cataract – Small
- Senior cataract – Large (filling the entire lens
Image Helen Haden
Nuclear sclerosis is an eye condition which resembles cataracts and the veterinarian will need to distinguish this from the cataract. Nuclear sclerosis occurs as the lens loses water due to aging, does not impede vision and requires no treatment.
- Blue/grey cloudy appearance in the pupil(s) of the eye
- Affected cats may bump into furniture or be more reluctant to explore as their vision declines
Other symptoms will vary depending on the underlying cause, for example, if diabetes is responsible, the cat may drink and urinate more often. A cataract may go unnoticed until it is quite large and/or signs of poor vision develops.
The veterinarian will perform a complete physical and ophthalmic examination using an ophthalmoscope, and obtain a medical history from you. He may notice blue/grey spots on the eyes.
Your veterinarian will perform diagnostic tests to determine the underlying cause which may include:
- 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
Some veterinarians will refer your cat to a veterinary ophthalmologist (eye specialist).
The goal of treatment is to address the underlying cause as well as remove the cataract.
Incipient cataracts may require close monitoring only, to ensure they don’t grow in size.
Phacoemulsification – Surgery to remove the lens and replace it with an artificial one.
Prior to surgery, eye drops will be placed in the eye to dilate (enlarge) the pupil.
A small incision is made in the cornea and a small opening is made into the capsule of the lens (capsulotomy) and an ultrasound probe emulsifies the lens which is then removed by suction.
The veterinarian inserts the artificial intraocular lens.
Administration of anti-inflammatory drugs and topical antibiotics to reduce inflammation and protect against postoperative infection.
Extracapsular lens extraction – Surgical removal of the entire lens if it is too solid to be break up, or the practice doesn’t have the necessary equipment for phacoemulsification.
In some cases, your cat may not be a suitable candidate for surgery, anti-inflammatory and/or antibiotic drops can relieve inflammation.
Your cat will wear an Elizabethan collar during recovery to prevent injury to the eye.
Administer all medications as prescribed by your veterinarian.
Watch for signs of infection such as redness, swelling and pain.
Follow up appointments are necessary to monitor progress and check for glaucoma, a build-up of intraocular pressure in the eye which can develop as a complication of cataract surgery.