Cataracts in Dogs

Dr Gemma Gaitskell (BVetMed MSc MRCVS, Royal Veterinary College, London)

 

Cataracts occur when there is a loss of transparency in the lens of the eye which becomes cloudy and increasingly opaque. They cause visual impairment and eventually blindness.

Many types of cataracts are inherited so testing of breeding dogs is important. The principal treatment for cataracts is surgical removal of the lens.

What are Cataracts?

Chihuahua with Cataract

Cataracts occur when the lens or the lens capsule in the eye becomes opaque and there are alterations in its transparency. The lens itself is a clear, asymmetrical, biconvex sphere shaped structure with an outer capsule, lens fibres and a central nucleus. The lens does not have any blood vessels or nerves inside it so nutrients must diffuse in from the aqueous humour, which surrounds it in the eye.

The lens’ function is to allow light and images to pass through it and focus them on the retina where visual information is carried to the brain via the optic nerve. When the lens becomes cloudy or opaque light cannot reach the retina as it should do, ultimately affecting normal vision. As dogs age, it is normal for the central nucleus of the lens to increase in density and become thickened and hardened and this should not be confused with cataracts, as sight is still normal.

How do Dogs Get Cataracts and When Are They Most at Risk?

Cataracts are often inherited in dogs and different types of cataracts are classified by the age at which they occur (congenital, meaning present at birth, juvenile or senile), the location they occur in, how severe the loss of transparency of the lens is, their rate of progression, their cause and their shape. Other causes of cataracts in dogs that are not inherited include:

• Metabolic causes, which are caused by conditions, such as diabetes mellitus and hypocalcaemia
• Trauma – blunt force or penetrating injuries to the eye can cause cataracts to develop
• Malnutrition
• Inflammation – caused by primary diseases of the eye, such as uveitis and neoplasia
• Radiation
• Toxic causes – caused by some medications

Which Breeds Are Most Commonly Affected by Cataracts?

It is common for certain breeds to be affected by cataracts and the breeds that have been proven to suffer from different types of inherited cataracts in the UK are known as Schedule A breeds and these include:

• Alaskan Malamute
• Australian Shepherd
• Belgian Shepherd
• Bichon Frise
• Boston Terrier
• Cavalier King Charles Spaniel
• German Shepherd
• Giant Schnauzer
• Irish Red and White Setter
• Large Munsterlander
• Leonberger
• Miniature Schnauzer
• Norwegian Buhund
• Old English Sheepdog
• Standard Poodle
• Chesapeake Bay Retriever
• Golden Retriever
• Labrador Retriever
• Siberian Husky
• American Cocker Spaniel
• Welsh Springer Spaniel
• Staffordshire Bull Terrier

Other breeds where cataracts are thought to be inherited but there is not yet a proven genetic link are known as Schedule B breeds and include:

• Border Collie
• Border Terrier
• Finnish Lapphund
• French Bulldog
• Greenland Dog
• Griffon Bruxellois
• Lancashire Heeler
• Field Spaniel
• Tibetan Terrier
• West Highland White Terrier
• Yorkshire Terrier

Symptoms of Cataracts in Dogs

A Labrador Retriever with Cataracts

Dogs have extremely good hearing and sense of smell and this means that they often compensate for their loss of vision with these other senses. Therefore it may not be evident that a dog has a cataract in the early stages. The following are some common signs of cataracts that are often seen in dogs:

• Cloudy opaque appearance to the eye
• Visual impairment, clumsiness, bumping into things
• Blindness
• Loss of confidence and increased caution, reticence to stray far from the owner
• Pain and/or redness in the eye

Diagnosis of Cataracts in Dogs

The majority of cataracts can be detected during an examination where the veterinarian will dilate the pupil and examine the eye. Depending on the results and type of cataract blood tests can be done to rule out any metabolic causes that may also need treating. Other tests, such as ultrasound, can be used to assess if there is any retinal detachment, which has more permanent consequences on sight before deciding on treatment options.

Can Cataracts in Dogs Be Treated?

Cataracts are usually treated by surgery to remove the lens that is affected. In dogs, this is usually more successful before a cataract is completely mature as inflammation and damage to other structures in the eye are less likely. As with any procedure there can still be complications, such as inflammation causing uveitis post-operatively. Other treatment options include phacoelmulsification, where ultrasound is used to fragment cataracts and the lens fragments are then removed.

In young animals with cataracts at birth topical treatments can be used to try and help reduce the size of the cataract as the rest of the lens grows normally around it, enabling some vision to be regained. The progression of the cataract often depends on its location and if a cataract is diagnosed it should be carefully monitored as some can mature very quickly, reducing the chances of success if surgery is chosen as a treatment option.

Preventing Cataracts in Dogs

In the long term preventing cataracts in dogs is largely based around responsible breeding and participation in canine health schemes, such as the eye scheme in the UK run by the British Veterinary Association (BVA). Breeds with a known predisposition to developing cataracts should be examined regularly, including when they are older to try and identify and eliminate bloodlines where cataracts are transmitted genetically. Although many dogs that are tested are pure-breed dogs intended for breeding, any dog can be tested under the eye scheme.

In addition to responsible breeding it is also important to rule out and treat any other potential causes of cataracts such as metabolic causes, such as diabetes or inflammatory causes as soon as possible to reduce the likelihood of cataracts occurring and progressing.

The Importance of Testing for Cataracts and Responsible Breeding

As with all conditions with a genetic component responsible breeding is paramount to reducing their incidence in the canine population. It is well recognised that cataracts are often inherited so it is especially important that breeding dogs are tested regularly. As part of the eye scheme they will be awarded a certificate with the results of any tests. Any dogs with cataracts should not be used for breeding purposes.