What are cataracts?
A cataract is any opacification of the lens of the eye. When an animal looks at an object, light rays are reflected from the object to the cornea (the outermost layer of the eye), through the lens (which focuses the rays), to the retina. In order for the lens to transmit light to the retina, a healthy lens must be transparent.
A partial or complete opacity of the lens can prevent the passage of light to the retina, resulting in impaired vision in the affected eye. Cataract formation is a progressive disease, and early treatment gives a better prognosis for preventing loss of vision.
What causes cataract formation?
There are numerous causes of cataract formation in cats and dogs including:
• Genetics – most cataracts are inherited and are known to occur more frequently in specific breeds of dogs and cats
• Congenital – some animals are born with cataracts (these tend to be non-progressive)
• Diabetes mellitus – only affects diabetic dogs, not diabetic cats
• Cataracts secondary to eye disease – cataracts may arise following glaucoma, progressive retinal atrophy (PRA), retinal degeneration, retinal dysplasia, retinal pigment epithelial dystrophy (RPED), and uveitis
• Spontaneous cataract formation – common in older dogs
• Nutritional disorders
• Trauma
• Miscellaneous – uncommon causes of cataracts include radiation, electrocution, toxic substances, etc.
Which dog breeds are genetically predisposed to cataract formation?
Genetic causes are the most common cause of cataracts in dogs. Cataracts can be inherited via recessive or dominant genes. The following are just a few of the dog breeds that have been associated with an inherited form of cataracts:
• Afghan Hound
• American Cocker spaniel
• Beagle
• Bichon Frise
• Boston terrier
• Chesapeake Bay Retriever
• Cavalier King Charles Spaniel
• German Shepherd
• Golden Retriever
• Labrador
• Irish Setter
• Retriever
• Miniature Poodle
• Miniature Schnauzer
• Old English Sheepdog
• Siberian husky
• Staffordshire Bull Terrier
• Standard Poodle
• Toy Poodle
• Welsh Corgi
• Welsh Springer Spaniel
• West Highland White Terrier
How do I recognize if my pet has a cataract?
It may not always be apparent to owners that their pet has a cataract. Many animals are adept at hiding or compensating for their growing blindness, and will show few signs of impaired visions. Signs to look out for are:
• Cloudiness of the eye
• A tendency to bump into things
• Uncertainty in strange environments
• Reluctance to climb stairs or jump up onto objects
• Other signs of blindness
• Signs of ocular discomfort that may indicate an underlying disease
• Signs associated with diabetes (e.g. drinking and eating excessively, urinating more than usual)
Pet owners should be aware that not all cloudy eyes are symptomatic of a cataract. Many older dogs have a condition referred to as nuclear sclerosis. This is a normal aging change to the lens which imparts the lens with a blue/grey appearance, similar to the appearance of a cataract.
However, nuclear sclerosis has no effect on vision. The two conditions can be easily distinguished by a veterinarian.
How are cataracts diagnosed?
A complete medical history and physical exam are necessary to identify cataracts and rule out any other causes of ill health. Routine blood tests may also be performed to exclude metabolic disorders such as diabetes mellitus.
Veterinarians should always perform a thorough ocular exam. The use of an ophthalmoscope (an instrument that aids in examination of the eye) will help to differentiate between simple cases of nuclear sclerosis and actual cataracts. However, a veterinary specialist may be required to further define the extent and severity of the cataract.
Additional diagnostic tests may be carried out to see if the affected eye (or eyes) is still capable of vision.
What is the treatment for cataracts?
There is no medical treatment that prevents or cures cataracts. The only treatment is surgical removal or ultrasonic dissolution of the cataracts, which are specialist procedures performed by a veterinary ophthalmologist.
These procedures should never be undertaken unless it is certain that vision can be restored to the eye. Important pre-operative conditions are:
1. There must be evidence of visual impairment – unilateral cataracts are generally not removed
2. The cataract must be the only reason that the animal cannot see well – there should be no history of impaired vision before the cataracts appeared
3. The extent of opacification should correlate with the degree of visual impairment
4. There should be no other signs of ocular disease present, such as retinal degeneration, retinal detachment, or uveitis
5. For a better prognosis, any underlying health problems should be resolved before undertaking surgery
6. Animals should have a temperament that is conducive to giving eye drops at home
Can cataracts be prevented?
It is not possible to prevent the development of cataracts. However, animals that are known to have an inherited or congenital cataract should not be bred from. If you are planning to breed from your animal, a veterinarian can perform an ocular exam to ensure that there is no presence of cataracts.
(photo: re-ality)