What is a Cataract?

A cataract is any abnormal opacity (cloudiness) of the lens or its outer covering (capsule). The opacity may range from a tiny spot to total loss of transparency.

The lens is a round shaped transparent structure that lies directly behind the iris and pupil. The cornea, aqueous humor, lens and vitreous body are elements that bend (refract) light waves to form an image upon the retina. The normal lens of the eye is a focusing device. It is completely clear and is suspended in position by special tissue fibers called “zonules” just posterior to the pupil. The lens focuses an image on the retina in the back of the eye.

Cataract formation is not associated with pain, redness, or tearing. The signs of a cataract are those associated with interference of vision. As the cataract matures, it becomes noticeable as a milky spot in the normally black pupil. When the area of clouding is small and away from the center of the lens, there may be little visual impedance. However, as the cataract progresses, it becomes larger and can cause blindness.


Cataracts can be congenital, age-related, of genetic origin (the most common cause), caused by metabolic diseases (diabetes mellitus), trauma, uveitis, dietary deficiency, radiation, electric shock, or by toxic substances. The patient with a cataract is not able to see through the opacity. If the entire lens is involved, the pet will be completely blind.


One common cause of cataracts is Diabetes Mellitus. In this condition a pet’s blood sugar increases as does the sugar level of the eye fluids. The fluid of the eye’s anterior chamber (see illustration above) is the fluid that normally nurtures the lens. However, in the diabetic pet, the lens can only utilize a certain amount of sugar. Excess absorbed sugar is transformed into sorbitol within the lens which draws water into the lens causing an irreversible cataract in the eye. Cataracts are unavoidable in diabetic dogs despite consistent insulin regulation. Diabetic cats have alternative sugar metabolism in the eye and do not get cataracts.

There are some dog breeds that are more likely to have cataracts. The most commonly affected breeds are cocker spaniels, miniature poodles, and miniature schnauzers. The following chart lists dog breeds commonly affected by hereditary cataracts.

As the animal ages, the lens cannot change it’s size and grow larger; instead, it becomes more compact with fibers. This condition is called Nuclear Sclerosis and is responsible for the cloudy-eyed appearance of older dogs. These lenses are still clear and the dog can still see through them (unlike cataracts).

A cataract can “luxate”, meaning it can slip from the tissue strands that hold it in place. The cataractous lens may become dislodged and can cause damage to the rest of the eye. If the lens winds up blocking the natural fluid drainage of the eye, Glaucoma (a build up in eye pressure) can result, leading to pain and permanent blindness. A cataract can also cause glaucoma when it absorbs fluid and increases in size thereby partially obstructing fluid drainage from the eye.

A small cataract that does not restrict vision is probably not significant. A more complete cataract may warrant treatment. Cataracts have different behavior depending their origin. If a cataract is of a type that can be expected to progress rapidly (such as the hereditary cataracts) it may be of benefit to pursue treatment when the cataract is smaller and softer, because surgery may be more effective.

Cataract treatment generally involves surgical removal or physical dissolution of the cataract under anesthesia. This treatment is invasive and expensive and is not considered unless it can restore vision. A complete examination of the eye is performed by a veterinary ophthalmologist. If a cataract is present, a test called an “Electroretinogram” is done to determine if the eye has a functional retina and could benefit from cataract surgery. Ultrasound of the eye can be used to look for retinal detachments. If the eye has a blinded retina, cataract surgery will not be successful.

The patient must be in good general health to undergo surgery. Diabetic patients must be well regulated before cataract surgery. In order for a patient to be a good candidate for surgery, the owner must be able to administer eye drops and post-surgical nursing care at home. It is important that before cataract surgery, the owner obtain from the opthamologist a clear explanation of what home care will involve.

If the patient proves to be an appropriate surgical candidate, the lens can be softened and sucked away using a technique called “phacoemulsification.” If the patient is relatively young, the lens is relatively soft and phacoemulsification is the first choice procedure. Older patients have much harder lenses and it is more common in these patients to simply remove the lens surgically. Pets with cataracts in one eye that can see in the other eye generally do not need surgery.

A prosthetic lens may or may not be inserted after the cataractous lens has been removed. Without the prosthesis, the dog’s vision will be approximately 20/800, and objects will appear to be reversed (as in a mirror). A prosthetic lens allows for normal restoration of vision. However, the incidence of uveitis (deep eye inflammation) after surgery is increased for patients receiving lens implants. After either surgery an artificial lens is usually placed for optimal post-operative vision.

All cataracts do not progress all the way to dissolution (inflammation) and may stay static or progress at changing rates. However, diabetic cataracts are notorious for reaching hypermaturity and creating inflammation.

Some degree of uveitis (deep inflammation) is unavoidable. This can cause a pupil constriction reaction which can increase the risk of scarring within the eye. Eye drops to keep the pupil dilated are usually effective in preventing this. Inflammation in the eye will resolve over time after surgery. Success rates are higher for cataract surgery if minimal inflammation is present in the eye prior to surgery [When uveitis is present prior to surgery, success (pain-free vision) is present in only 50% of cases 6 months after surgery as opposed to 95% of cases for whom there was no uveitis preoperatively]. Therefore, pre-operative anti-inflammatory eye drops are frequently prescribed.

Another complication involves the development of opacities on the remaining lens capsule. In humans, laser surgery is used to remove the lens capsule but in the dog, the capsule is too thick for this procedure. Some ophthalmologists prefer to remove the capsule as a preventive measure.

Bleeding after surgery can be another significant complication and can be caused by excess barking or activity after surgery. Small bleeds are not significant, but a large bleed could affect vision.

Complications to consider are:

• Long term uveitis (probably of most concern for diabetic patients)
• Opacification of the lens capsule (usually correctable with laser)
• Corneal clouding (can be managed with 5% saline eye drops 4 to 6 times daily)
• Bleeding into the eye
• Glaucoma
• Retinal detachment (particularly if the cataract is hypermature)

OVERALL, A 90% SUCCESS RATE IS DESCRIBED
AFTER CATARACT SURGERY

An Elizabethan collar is very important after surgery because if patients’ rub or paw the eye, damage could occur. Topical therapy (eye drops) will be needed for several months after surgery. Your pet’s surgical recovery will need to be closely monitored by your veterinary opthamologist and regular veterinarian.