Cataract is a disease of the lens of the eye in which the normally clear lens becomes opaque or white. This interferes with vision and can result in blindness. Many owners confuse a less serious problem of older dogs eyes with cataract. In some cases an eye specialist may be able to operate on the eye to remove the cataract.
Light enters through the front of the eye and is focused by the clear lens onto the retina, which lies at the back of the eye. Information from the retina is transmitted to the brain where processing occurs.
For the lens to work correctly, it must be perfectly clear. In cataract, the lens becomes opaque (like frosted glass) or even completely white. Light does not pass through it well in this state and vision is reduced. Severe cataracts cause blindness.
There are several different causes in dogs:
- Cataract development can be inherited from parents in many different dog breeds. Hereditary cataracts affect both eyes – usually, but not necessarily, at the same time. Hereditary cataracts can be present at birth (congenital) or, more commonly, they may develop in young adult dogs.
- Cataracts are common in dogs suffering from sugar diabetes due to disturbances in the metabolism of the lens caused by abnormal blood glucose levels.
- Cataracts can arise following severe inflammation in the eye, or as a result of poisonings or nutritional imbalances.
- Cataracts can also be associated with glaucoma (increased pressure within the eyeball), disease of the retina (at the back of the eye) and when trauma has resulted in dislocation of the lens of the eye from its normal position.
Usually owners are alerted to the fact that their pet may have a problem with its eye when they notice a whiteness of the eye. If eye disease develops gradually, dogs are often able to adapt well and use their other senses to help them get around. Dogs have very good hearing and a sense of smell and can use these to compensate for poor vision to some extent. In familiar surroundings it may be almost impossible to tell that a pet cannot see. If you are worried about your pets vision you can test it yourself using some simple exercises:
- Observe your dog carefully in the home environment and out of doors
Does he appear to be having any visual difficulty?
- Throw light, silent objects (e.g. a ball of cotton wool) in front of your dog’s eyes
Does he see and follow these?
- Construct a small obstacle course in the home, or move furniture around and away from the usual positions
Does he see and avoid these obstacles the first time?
Repeat the above tests in daylight and in subdued lighting.
If you are concerned about the results of the report them to your veterinary surgeon and ask for a check-up for your pet.
In older dogs, the lens of the eye may take on a bluish or grayish color. Many owners believe this is a cataract. However, a simple eye examination usually provides the necessary reassurance. This problem is called nuclear sclerosis and is part of normal ageing. Vision is preserved and no specific treatment is needed.
Diagnosis is usually straightforward, and based upon visual testing of the dog and examination of the eye by a veterinary surgeon/ophthalmologist. Additional tests may be required to check for diabetes and occasionally other causes and other eye diseases.
Cataracts are treated by removing the lens from the eye. The lens is surgically removed by a specialist. There are several different techniques but one of the most popular is known as phacoemulsification (the use of ultrasound waves to break up the cataract). Once the lens has been broken up fragments can be removed through a small incision in the eye. Other surgical techniques are also possible and may be indicated in certain cases, e.g. when lens of the eye has become displaced.
Following surgery the aftercare is very important. Eye drops may be required for several months and must be applied regularly at home. If cataracts are present in both eyes, they may be removed at the same time, thus avoiding the need for further surgery in the future.