The term "cataract" refers to any opacity of the lens of the eye. Dogs of either gender can develop cataracts, and some breeds are especially at risk. Cataracts are more common in older animals but can be present at birth or develop very early in life. Cataracts affect a dog's vision and can be progressive, leading to blindness
Causes of Cataracts in Dogs
In dogs, cataracts typically have a strong hereditary component. Other contributing causes include nutritional deficiencies, low blood calcium levels, exposure to toxins, diabetes mellitus, radiation, electric shock and blunt or penetrating trauma. Cataracts can occur spontaneously for no known reason. The actual biological cause of cataracts is a change in the protein composition or arrangement of the fibers of the lens of the affected eye.
Prevention of Cataracts
The only truly effective way to reduce the prevalence of cataracts is to remove affected animals from any breeding program. Board certified veterinary ophthalmologists can screen animals for cataracts. However, even removing affected dogs from a breeding program will not guarantee that future generations will be free of the condition. Early diagnosis and management of diabetes mellitus also can help reduce the chance of cataract development. However, once cataracts due to diabetes develop, they are irreversible.
While cataracts always affect a dog's vision, they do not affect its health. Most dogs adjust to their vision deficiencies extremely well. Surgical treatment for cataracts is highly successful, and the prognosis for dogs with cataracts is excellent if the condition is identified and treated early. Owners should know that not all cataracts are progressive, and not all affected dogs need surgical correction.
The term "cataract" refers to any opacity, regardless of size, of the lens of the eye. Dogs of either gender can develop cataracts for a number of different reasons, although in dogs most cataracts have a genetic component. Cataracts become more common with increasing age, although some can be present at birth (congenital cataracts) or develop early in life (juvenile cataracts). Other causes include nutritional deficiency, elevated blood glucose levels due to diabetes mellitus, exposure to toxins, radiation and blunt or penetrating trauma. All cataracts are essentially caused by some change in the protein composition of the lens of the eye or in the arrangement of the lens fibers. Regardless of the cause of cataracts, the clinical signs in domestic dogs are the same.
Symptoms of Cataracts in Dogs
The chief complaints by owners of dogs with cataracts are cloudy, white-ish or blue-grey pupils (or spots in the pupil) and impaired vision. Cataracts can occur in one eye, as is usually the case when cataracts are caused by injury, or they can occur in both eyes. Cataracts can appear suddenly (owners often report that they happen "over night"), or they can develop slowly over a period of years. The cloudiness of the lens may have a crackled appearance, or it may look like a chip of ice. The cataract may appear as a bluish-grey haze over the entire pupil, or only over a part of it. Cataracts will always affect a dog's vision. Depending on the severity of the cataract, affected dogs will display a range of vision problems from mild to complete blindness. Some of the signs associated with reduced vision include a high-stepped walk, unsure footing, tripping over or bumping into objects, walking into walls, misjudging distances and not recognizing people. Owners of dogs with cataracts may observe some or all of the following symptoms:
Cloudy pupils in one or both eyes
Signs of vision impairment (bumping into walls or other objects, tripping, misjudging distances, not recognizing familiar people)
Increased intake of water and increased frequency of urination in dogs with diabetes mellitus
If your dog displays any of these symptoms, especially if you notice any cloudiness in your dog's eyes, it is important to make an appointment with your veterinarian as soon as possible. Cataracts are normally painless, but they can cause inflammation and result in permanent eye damage if left untreated. To date, the only effective treatment for cataracts is surgery. Your veterinarian can help you decide whether surgery is necessary or appropriate and whether anti-inflammatory medication is needed.
Dogs at Increased Risk
Older dogs develop cataracts more often than younger dogs, although dogs of any age are at risk. Dogs suffering from diabetes mellitus also tend to develop cataracts more frequently than other animals. Breeds with the highest prevalence of cataracts include the Smooth Fox Terrier, Havanese, Bichon Frise, Boston Terrier.
Cataracts in our companion dogs are not difficult to diagnose. If an owner suspects that her dog may have developed cataracts or any vision problem, she should have her dog's eyes examined by a veterinarian. Owners may be referred to a specialized veterinary ophthalmologist for advanced testing. The veterinarian will perform a series of tests to confirm the presence of cataracts or to determine what is causing the changes to the dog's eyes and vision.
How Canine Cataracts are Diagnosed
As a dog enters the clinic or examination room, the veterinarian will watch how the dog walks to look for any obvious signs of vision difficulties. The initial work-up will include an evaluation of pupil size and symmetry and an assessment of the dog's pupillary light reflexes. The veterinarian probably will check the "menace reflex" by moving one hand swiftly toward the dog's face, then stopping abruptly, checking for a blink reaction. Another test frequently done to detect vision deficiencies is to throw a cotton ball onto the floor while watching to see if the dog follows the movement. Blood and urine glucose levels will likely be assessed as well, to determine whether diabetes mellitus is a contributing factor to the dog's vision problems.
The intraocular pressure of the 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 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 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 check the moisture level of the eye, look for foreign bodies and determine whether damage to the cornea has occurred. Advanced testing may include ocular ultrasound and electroretinography to evaluate the retina and rule out concurrent retinal degeneration. These tests are usually performed if surgery is anticipated. Most of these advanced diagnostic tests typically are performed by a veterinary eye specialist.
If your dog shows signs of vision disturbances, contact your veterinarian. Cataracts usually are quite treatable surgically.
Dog owners should seek veterinary advice if they suspect that their dog has cataracts or other vision problems. Dogs with uveitis (inflammation of certain interior structures of the eye) should be treated with topical anti-inflammatory medication, but the only effective treatment for cataracts is surgery. A thorough eye examination is important, because cataracts can progress rapidly. Short of blindness, cataracts can progress to glaucoma and to retinal detachment, at which point surgery may no longer be a viable treatment option.
The only realistic treatment for dogs with impaired vision due to cataracts is surgery. The goals of surgery are to restore vision and hopefully prevent the common secondary sequellae of cataracts, which are uveitis, glaucoma and retinal detachment. The prognosis for dogs undergoing surgical removal of cataracts is better if it is done early in the course of cataract development. Of course, a veterinarian will want to be sure that the dog is otherwise systemically stable and healthy prior to surgery. For example, dogs suffering from diabetes mellitus should have that disorder controlled and their blood glucose levels normalized before having surgery for vision problems. However, it is particularly important to remove cataracts associated with diabetes mellitus, because those cataracts can cause rapid deterioration of vision and ultimately blindness if left unchecked.
Cataract surgery usually requires preliminary ophthalmic ultrasound and an electroretinogram to check whether the posterior part of the eye is normal. If it is, the veterinary ophthalmologist 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 normal vision. Without this artificial lens, dogs will be extremely far-sighted after cataract surgery, with little useful remaining vision. After surgery, the dog may be placed on exercise restriction for several weeks, may need to wear an Elizabethan (cone) collar and may also be given topical antibiotics and anti-inflammatory medications, sometime long-term. Regular re-checks by a veterinary ophthalmologist are recommended as well. 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.
Without treatment, most dogs with cataracts will lose vision in the affected eye. With surgical correction, 90% to 95% of dogs will have their vision restored successfully. Early diagnosis and treatment are of course very important to the outcome for each affected animal.