Situated inside the eyeball is a clear lens that helps your dog to focus light. A cataract is an opacity (white colour) within the lens. This can range from a small cataract (incipient) that doesn’t interfere with your dog’s vision, to a cataract that involves the whole of the lens (mature) and causes blindness.
As our dog ages the lens fibres harden and give the lens a blueish/greyish colour, this is called nuclear sclerosis and should not be confused with a cataract. Your vet/ophthalmologist should be able to differentiate between the two by looking at the lens with a special instrument called an ophthalmoscope. Nuclear sclerosis will affect your dog’s ability to focus on near objects. The same happens with us as we get older so that we require glasses to read. However, dogs do not require good near vision as with humans, so vision is only minimally affected.
There are numerous causes for the formation of cataracts which include:
Many breeds in NZ can develop hereditary cataracts. These include Bichon Frise, Staffordshire bull terrier, Boston terrier, Poodle and Labrador. Some breeds develop cataracts when the dog is young or even at birth and progress to total blindness, whilst in others the cataracts stay small and don’t tend to progress. Often the sire/dam of the dog only carries the genetic defect but don’t have a cataract themselves, this is called a recessive gene. Fortunately for some breeds we can now check their DNA for hereditary cataracts prior to breeding.
In approximately 75% of diabetic dogs, cataracts will develop within the first 9 months of diagnosis. This is due to a build-up of sugars within the lens which draws water in. These cataracts develop very rapidly, within 3-5 days the dog can become completely blind.
These develop as our pet ages, usually over 8 years old. They are often small and don’t interfere significantly with their vision.
Either direct damage to the lens of the eye for example with a cat claw, or a direct blow to the eye, or by damage to surrounding structures within the eye which affect the lens.
Various diseases of the eye, for example uveitis (affecting the iris), glaucoma (increased fluid within the eye), or retinal disease can ultimately lead to a cataract formation by affecting the nutrition of the lens.
Often as an owner we may notice that our dog’s pupil is looking a milky colour as opposed to being black. There also may be changes in your dog’s behaviour that may indicate their vision has deteriorated - such as failing to catch a ball, appearing clumsy or walking into objects. Sometimes your vet will pick up a cataract by examining the lens at a routine veterinary visit.
In many circumstances if the cataract is small, non-progressive and not affecting your dog’s quality of life it may be that the recommendation is to monitor your dog only. Certain breeds such as the retriever often have non progressive cataracts. If however the cataract is affecting vision and is progressing, it is recommended to see a veterinary ophthalmologist (eye specialist) so that he/she can assess the best treatment for your dog. If the cataract is mature (involving the whole eye) and is left, it may start to leak or fall forwards or backwards in the eyeball. This can cause permanent damage to the rest of the eye by causing glaucoma (increase in fluid in the eye), uveitis (inflammation of the coloured part of the eye) or damage to the retina. Once cataracts are present there is no medical means of dissolving them, cataract removal is the only option. If the ophthalmologist recommends that your dog is a good candidate for cataract removal, then under a general anaesthesia he/she uses a special instrument that is inserted into the lens and uses high frequency ultrasonic waves to break down the cataract, which is then sucked out. This procedure is called phacoemulsification. Some ophthalmologist will insert an artificial lens whilst others do not. The cornea (front part of the eye) actually focusses a large amount of light so the lens is less important – especially with dogs that do not have to read small print! Approximately 90% of dogs have good vision after cataract surgery but there can be complications and your dog will need various medications and close monitoring both before and after surgery. Obviously cataract surgery is an expensive procedure as it involves specialist skills and very expensive equipment.
Firstly it is important to monitor your dog’s eyes regularly to make sure the eye is not becoming painful from cataract induced damage eg glaucoma/uveitis. Secondly, dogs can still have a good quality of life despite limited vision or complete blindness, as they often manage using their other superior senses to get around eg smell/hearing. In addition if the environment stays the same they can use ‘memory maps’ to negotiate around the house.