Cataracts (Opacity of the Lens) in Cats

What are cataracts?

The lens is a transparent crystalline structure encased in a capsule that sits behind the pupil and iris (the coloured part of the eye) and is made up of an outer capsule, epithelium and the lens fibres that are laid out in layers like an onion.

How the lens works:

When light enters the eye, the lens adjusts its shape to focus incoming light on to the retina, the thin, transparent layer of light-sensitive tissue which lines on the rear wall of the eye. The retina converts light into electrical impulses and transports them to the brain via the optic nerve.

A cataract is a clouding/opacity of the lens, which reduces the amount of light reaching the retina which leads to vision impairment and eventually blindness. This is a similar effect to that of a frosted window; it is still possible to make out shapes and shadows, but not much more.

Cataracts can affect a part of or the entire lens and can be unilateral (one eye) or bilateral (both eyes). The larger the area affected, the greater the impact on 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.

Advanced cataracts lead to lens-induced uveitis due to the leakage of proteins through the lens capsule.

Causes

The most common cause of cataracts in cats is uveitis, other causes include the following:

• Natural aging process
• Trauma
• Inflammation
• Electric shock
• Metabolic disorders (diabetes, hypocalcemia, and hypoparathyroidism)
• Poor nutrition during kittenhood
• Prenatal influences
• Certain drugs (antibiotics and steroids)
• Toxins

Cataract classification:

• Incipient (immature) cataract: Very small
• Immature cataract: Small
• Senior cataract: Large (filling the entire lens)

Symptoms

• 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 develop.

Nuclear sclerosis is an eye condition that 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.

Diagnosis

The veterinarian will perform a complete physical and ophthalmic examination after dilating the pupils. Blue/grey spots may be visible in one or both eyes.

Diagnostic workup:

• Baseline tests: Biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat, check for electrolyte imbalances, glucose levels, infection or inflammation.
• Imaging: Ultrasound of the eye may be necessary if the cataract is too cloudy to examine the retina
• Slit-lamp examination: This test involves the use of a slit lamp to see the front of the eye under magnification
• Electroretinogram (ERG): A measurement of the electrical responses to a light stimulus of the retinal photoreceptors (rods and cones), inner retinal cells and ganglion cells to evaluate the function of the retina at the back of the eye. The pupils are dilated with the use of medications and electrodes are placed on the cornea, bulbar conjunctiva or the skin below the lower eyelid. Flashes of light entering the eye trigger small amounts of electricity in the cells of the retina which are measured to determine how well they are working.
  

Some veterinarians may refer your cat to a veterinary ophthalmologist (eye specialist).

Treatment

The goal of treatment is to address the underlying cause as well as remove the cataract.

Treatment will depend on the size of the cataract. Small (incipient) cataracts may require close monitoring only, to ensure they don’t grow in size. Underlying conditions such as lens-induced uveitis, diabetes or Cushing’s disease must be brought under control before surgery.

Candidates for cataract surgery include cats who have a good menace response, pupillary light reflex and dazzle response. These are basic tests to evaluate how the cat responds to various ocular stimuli.

Surgical treatment:

Large will require surgery to remove the lens and replace it with an artificial one (intraocular device) if the cat is a good surgical candidate. In most cases, the surgeon will operate on one eye.

There are two methods to remove the lens, phacoemulsification and extracapsular lens extraction.

Cataract surgery is performed as an out-patient procedure, which means in most cases, the cat will be admitted on the day of surgery and discharged later that day.

Phacoemulsification (pronounced fako-emulsification)

• Before surgery, eye drops will be placed in the eye to dilate (enlarge) the pupil.
• The surgeon makes a small incision in the cornea and the lens capsule (capsulotomy), and an ultrasound probe utilises bursts or pulses of ultrasound energy to break up the material within the lens which is then removed by suction.
• The veterinarian inserts the artificial intraocular lens into the lens capsule and the surgery site is stitched shut.
• 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 broken up, or the practice doesn’t have the necessary equipment for phacoemulsification, once the lens is removed, the artificial intraocular lens is inserted into the lens capsule.

If the cat is not a suitable candidate for surgery, anti-inflammatory and/or antibiotic drops can relieve inflammation.

Home care

The 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.