Cataracts in Dogs
by Dr. Audrey Harvey, BVSc (Hons)
There are several ways of classifying cataracts in dogs, depending on the cause (primary or secondary), where they are positioned on the lens, and how complete they are.
The main function of the lens in your dog's eye is to transmit light, and focus that light sharply on their retina. To do its job, the lens must be transparent. If it loses that transparency, it is said to have a cataract.
It's important to differentiate between cataracts and nuclear sclerosis, which is a normal part of getting older in dogs. The lens becomes hazy and has a cloudy appearance, but there is no loss of vision. Most dog owners notice it in passing, because it isn't usually very severe, and it doesn't cause their canine companion any problems.
If everything else in the eye is working as it should, cataracts in dogs have to be quite advanced before their eyesight is affected. However, they can cause uveitis, a painful inflammation of the middle layer of the eye.
Causes of Cataracts in dogs
Primary cataracts in dogs are genetic, particularly in young pure bred animals. It's important to understand that cataracts can be genetic without being hereditary. There can be a random abnormality in development of the eye during a dog's time in the womb, and they may be born with eye disease. If there is no other obvious cause of a dog's lens opacity, then it is assumed to be genetic.
Poodles, spaniels and retrievers all suffer from hereditary cataracts. The Canine Eye Registration Foundation keeps thorough records of eye diseases in dogs and the breeds affected. Responsible breeders have their dogs assessed by an ophthalmologist before they are bred, to reduce the incidence of hereditary eye disease in their breed. They are given a certificate indicating that they are clear of eye diseases that could be inherited by their puppies.
There are many other conditions which can also lead to cataract formation.
1. Uveitis is an inflammation of the iris and related tissues. The inflammation can spread to the lens, and lead to opacity.
2. Trauma such as a penetrating wound can result in severe infection and inflammation in the eye. This can cause cataracts.
3. Retinal disease is often associated with cataract formation. Nobody really knows if these conditions are connected, or whether a dog with one hereditary eye disease such as progressive retinal atrophy may also have other genetic eye conditions.
4. Cataracts are a common consequence of diabetes, because of abnormal sugar metabolism. They can occur even if the diabetes is well controlled with insulin and a strictly controlled diet.
5. Some dogs develop cataracts just because they are getting old. The reason for this isn't known.
Diagnosing Cataracts in Dogs
The first indication that your dog may have a cataract is a white area in the middle of their pupil. It may affect one or both eyes, and it isn't usually painful.
Just because your dog's lens has an opaque white area, it isn't necessarily a cataract. Other conditions that can look like cataracts are remnants of the pupillary membrane, and pigments from the back of the iris which can be seen on the front of the lens. Some dogs develop white lines or spots on their lens; again, nobody really knows why this occurs.
Veterinarians use several diagnostic tools to confirm that cataracts are present in your dog's eye. The easiest and least invasive is a thorough examination of the eye with an ophthalmoscope. This can detect lens opacity and any abnormalities of the retina. It will also indicate if their reaction to light in the eye is normal or reduced.
Blood tests are important in ruling out diabetes as a cause of cataracts. However, dogs with diabetes are often already showing symptoms such as excessive thirst, and blood tests will just confirm this.
More advanced diagnostic methods include ultrasound of the lens, and testing the electrical activity of the retina. These are specialized procedures, and most dogs with cataracts are usually referred to an ophthalmologist for treatment.
Treating Cataracts in Dogs
Cataracts are just like other medical condition in dogs, in that early and aggressive treatment usually has the best outcome.
Laser surgery isn't yet available for dogs, and the only specific treatment for their cataracts is removal of the lens. There are several ways of doing this.
The opaque lens can be surgically removed. This is very effective, although if there is any uveitis or inflammation, then the outcome isn't as good. Surgery is best performed when the cataract is fairly young, to try and avoid lens induced uveitis and get better results. The pupil is dilated with drugs, and the cornea is cut. From this point, the ophthalmic surgeon has several alternatives.
Firstly, the capsule, or cover, around the lens can be cut open. The whole lens is carefully removed, and an artificial lens is be inserted. The capsule is then sewn shut.
Secondly, the whole lens and its capsule can be removed all at once. If a dog has this procedure and needs an artificial lens, then the lens needs to be stitched in place. There is no capsule to hold it in place.
Phacoemulsification is the best way of treating cataracts in dogs, and is up to 95% successful in improving their vision. The pupil is dilated, and a small cut is made in the cornea. The lens capsule is opened, and sound waves are used to break up the lens. The fragments are then removed, and a prosthetic lens is inserted into the capsule.
No matter what method is used to treat cataracts in dogs, it's important that post operative care instructions are followed very closely. Any uveitis or inflammation in the eye needs to be treated. Your veterinarian may prescribe eye drops or tablets that need to be administered on a regular basis, both before and after their operation. It would be a shame to put your dog through an uncomfortable and expensive surgical procedure, only to have it fail because they weren't looked after properly afterwards.
If your dog has secondary cataracts, it's essential that their underlying disease is correctly treated. In these cases, surgery isn't usually recommended.
Cataract removal usually results in improved eyesight, whether or not an artificial lens is inserted. However, this isn't always the case. The retina at the back of the eye is a vital component of your dog's vision. When your dog has a cataract, it is very difficult to get a good look at the retina, and make sure it is normal and healthy. There have been several cases where a dog underwent successful cataract removal, but they had underlying retinal disease, and their vision didn't get any better.
Uveitis associated with cataracts in dogs, can lead to glaucoma, a painful increase in fluid pressure in the eye. This has effects on the retina and can lead to blindness. Anti-inflammatory medication is a vital part of treatment of uveitis, and is often used before and after lens removal.
If all goes well with surgery and after-care, then most dogs with cataracts can see quite well after their operation. However, regular check ups are essential to make sure the eye stays healthy, and to catch any complications before they become too serious.
Even if your dog loses its vision, it can adapt very well. Don't leave objects on the floor around the house, keep its environment as consistent as possible, and never allow your dog off leash. In spite of these limitations, it can still enjoy a happy and fun filled life.
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