CANINE CATARACTS

Michel (Mike) B. Rubini


The most common cause of blindness in dog breeds, including the Volpino Italiano is an opaque clouding
of the lens called cataracts. Clinically there are several variants and / or stages of cataract development.


- Incipient cataract - The opacity in the lens is very small the cataract may have no or
minimal effect on the dogs vision.
- Immature cataract – The opacity of the lens will be larger and cause a blurring of the vision.
- Mature cataract - The opacity of the lens has developed to the point where all functional
vision is lost.
- Hypermature cataract – this type of cataract starts to reduce in size due to a loss of water
and nutrients


In most cases incipient and immature cataracts will develop into a mature cataract.
It should be noted that as any dog ages they develop a hardening of the lens that appears bluish-greyish.
As the dog ages the blue color can intensify. This hardening of the lens, called nuclear sclerosis (also
known as Presbyopia) is normal in ageing dogs. It will usually take an ophthalmologist to distinguish
between nuclear sclerosis and cataracts or to determine if both are present.

 

The lens is a soft, clear crystalline structure
that allows light to pass through it and be
focused on the retina. It can be thought of as
being functionally equivalent to a camera lens.

 

When the lens loses its transparency and
becomes cloudy it then lessens the amount of
light that can pass through it. Eventually
most light is ‘blocked’ and the animal becomes

blind.

Cataracts are formed when the fibres of the lens breakdown from their usual arrangements. If the biomechanical exchange system that forces sodium water mixture through the eye is disrupted or breaks down it will then allow extra water to be pumped into the lens. This changes the normal composition in the lens (water 66% to protein 33%) and so increases the amount of water insoluble proteins. Cataract formation starts and the crystalline lens become less transparent.


There are many different types of cataracts and they affect all breeds of dogs. They can be inherited, caused by aging, injury, poisoning, radiation or electric shock. It can also be caused by toxicity in the eye or a simple lack of nutrition. Cataract formation can vary in ages of onset and the speed of development in the canine eye. However there are breeds that are more susceptible to cataract formation than others. Although cataracts are mechanically well understood a great deal of information is still not known about its onset, development and the genetic formation of the cataract.
 

Inherited cataracts - Most cataracts are inherited! In many breeds the cataract is often caused by a mutation of the HSF4 gene, which is autosomal recessive. In this case of HSF4 the opacity starts small in the back of the lens, growing until a mature cataract is formed. The growth of the cataract is variable though; some dogs go blind quickly while a few others may outlive the growth with fairly clear vision.
The cataract may occur between the age of 9 and 15 months and is generally mature in 2 to 4 years.
Genetic testing is available for a number of breeds to ascertain if the cataract is a genetic formation or
not.


Diabetic cataracts -The second most likely cause of cataracts in dogs is diabetes mellitus. Seventy five
percent of diabetic dogs will develop cataracts with a year of diagnosis. With diabetes the excess sugar
in the lens cannot be consumed and is transformed into sorbitol. The sorbitol draws excessive water
into the eye leading to the cataract formations. Sometimes diabetic cataracts can develop in days. This
may be the first sign of diabetes in dogs and an assessment should be done quickly for diabetes.
Unfortunately cataracts are virtually assured in any dog that is diabetic, regardless of insulin treatment.


Toxic Cataracts - Cataracts can also be the side products of toxicity or illness in the eye, such as
progressive retinal atrophy (PRA), glaucoma and uveitis. In many cases the illness will be known in
advance so the cataract may be expected. In PRA, the most common form of toxically formed cataracts
the ‘death’ of the rods and cones in the retina release a toxicity as a by-product that is absorbed by the
lens, causing the development of the cataract. Toxic cataracts can also form from ingested lead and
inadvertent poisonings from various herbicides (especially Glyphosate exposure which is commonly

found in ‘Roundup’). It may also be caused by commonly available medications for flea, tick and
heartworm prevention.


While cataracts are often not painful they can cause inflammation as the modified liquid in the lens
leaks into the eye. In a hyper-mature cataract the lens capsule begins to shrivel because of autolysis of
the lens fibers. It is also possible at this stage for the cataract/lens to become luxated which may cause
damage and inflammation to the rest of the eye including secondary Glaucoma. At this stage the animal
can feel discomfort and/or extreme pain.

The only effective treatment for Cataracts is lens replacement surgery. While supplements are
advertised as an effective way to stop or reverse the cataract (some advertisements claim it can stop
PRA) there is simply no evidence of it. Various antioxidants, vitamins and zinc are needed for a healthy
eye and it is possible it may slow the growth of a cataract. If the cataract has not progressed to a later
stage it will probably do no harm yet may simply be a waste of money.


July 2014
Michel (Mike) B. Rubini mike@rubini.ca

©  2011 - 2019 Mike Rubini and Terralea Collins

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