EYE CONDITIONS

CATARACTS

Cataract is the medical term referring to opacity (cloudiness) - in the lens. it is due to a breakdown of the normal structure. Cataracts can range in size from a barely detectable spot to involving the entire lens. Even small opacities in the lens can result in blurred vision or glare problems.

The lens is an avascular structure whose primary purpose is to help focus light onto the retina. Because of constant growth and compression of the lens epithelial cells, the density and volume of the lens increase with age. The increased density of the lens in older dogs cause the eyes to appear "bluish gray" and hazy. This phenomena is called "nuclear sclerosis" and should not be mistaken for a form of cataract, as the dog will continue to have clear vision. Nuclear sclerosis also occurs in older people, who you may notice have a bluish gray color to their eye.

Cataracts can be classified according to age of onset: congenital, developmental (juvenile), and senile A congenital cataract is present at birth. It may be inherited or teratogenic (a teratogen is any substance that causes abnormalities in the developing fetus). Developmental cataracts appear from birth to about six years of age. Most of these are hereditary. Senile cataracts are seen in old age, and their cause is unknown. Many factors may be involved.

The majority of cataracts seen in dogs under six years of age are inherited cataracts.² Other causes of cataract formation include nutritional, metabolic, toxic, traumatic, and infectious causes, endocrine dysfunction, and intraocular disease. Cataracts have been reported in experimental dogs given diazoxide (an antihypertensive drug) and DMSO (dimethyl sulfoxide). Diabetes mellitus will cause cataracts in dogs. A traumatic incident such as thorns, or twigs penetrating the lens capsule can cause temporary or permanent cataracts.

Usually the cataracts are first diagnosed in dogs six to eighteen months of age. These cataracts resemble the so-called classic "retriever cataract". This is the triangular-shaped cataract, positioned in the middle of the back part of the lens. It is usually slowly progressive and often remains small enough not to affect vision. The inheritance has been suggested to be by an autosomal dominant gene with incomplete penetrance as reported in other breeds.

 Several inherited cataracts have been described. The juvenile or developmental "retriever cataracts" can be diagnosed at six to eighteen months of age. Again, this cataract is slowly progressive and often remains small enough not to affect vision. This form of cataract is the result of a dominant gene. Most dogs have only one "dose" of the dominant gene. However, if both parents contribute the gene such that the offspring contains two "doses" of the gene, the cataract may progress to involve most of the lens. This results in vision loss and only cataract surgery with lens replacement with an artificial lens will return functional vision to the involved eyes.

Another from of cataract in the Labrador Retriever is a small to medium sized cataract which is very slowly progressive. It first appears in the front part of the lens. This cataract rarely results in loss of vision. It usually develops in dogs five years or older. The pattern of inheritance is currently unknown.¹

Cataracts due to old age develop in dogs as they do in people. After six or seven years of age the lens of the dog begins to harden. This can result in relative farsightedness and dogs may seem to be out Of focus for close vision. People with hardening of the lens require glasses to read. Eventually the lens becomes so hard that the proteins in the lens begin to deform, take on water and a senile cataract develops. Senile cataracts are not inherited but are the result of aging of the eye. If they become sufficiently advanced, cataract surgery can be done as long as the retina and other structures of the eye are functional.¹

Animals diagnosed with cataracts should not be used for breeding .The prudent approach is to assume cataracts to be hereditary except in cases known to be associated with trauma, other causes of ocular inflammation, specific metabolic diseases, persistent pupillary membranes, persistent hyaloid or nutritional deficiencies.

Eye Anatomy
To review the anatomy of the eye, the eye functions to collect images and pass this information to the retina. The retina are the cells that translate the image to the brain, which creates visual images in the nervous system. The eyelids protect the surface of the eye, especially the cornea, which is the clear outer window of the eye. The ophthalmologist looks through the cornea to evaluate the lens and retina of the eye. The cornea protects the eye and also helps to focus light into the pupil or opening in the iris. The lens is located behind the iris and is important for the fine focusing of light images into the back part of the eye where the retina is located. The canine retina contains mostly rod cells (18:1) and only a few cone cells are present. For this reason researchers believe that most dogs only have limited colour vision. However, the ability of the dog to see at night is likely to be superior to that of a person.

How Do Cataracts Form

Despite the fact that there are several different forms and causes of cataracts, they all develop in a similar fashion. The normal lens is maintained in a dehydrated state. It consists of 66% water and 33% protein. There is a complicated sodium water pump system in the lens that keeps this water/protein balance in check. When the biomechanical system in the lens is damaged, this pump system begins to fail and extra water moves into the lens. In addition, the percentage of insoluble protein increases. These changes result in the loss of transparency and cataract formation.

Treatment

Treatment for canine cataracts consists of surgical removal of the lens. There is currently no good non-surgical treatment for this condition. With the increase in veterinary surgical skill and equipment, the surgical procedure to remove the problem lens is becoming increasingly more common. There are several different techniques used to remove the affected lens including; the removal of the entire lens and surrounding capsule, the removal of the lens leaving the surrounding capsule, phacoemulsification of the lens, and aspiration and desiccation of the lens. All of these techniques can offer excellent results. For a successful outcome, the affected animal must undergo a thorough examination to determine if it is a good surgical candidate. Diabetic animals that are not regulated, aggressive animals that are difficult to treat daily, or animals in poor or failing health, are not good surgical candidates. If you suspect your dog is developing cataracts, then you should work closely with a veterinary ophthalmologist to take the best and most effective course of treatment for the dog.

It is recommended that all breeding stock which is related to a dog with diagnosed cataracts, is tested by a veterinary ophthalmologist to minimise passing the problem on.

As with any canine health problem, there is no shame in admitting to a problem, this is to be encouraged. The shame lies in ignoring it!

List of dogs affected with Hereditary Cataract in Finland

Dogs affected with HC in Sweden

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