Cataracts are a problem that can affect the eyes of both people, dogs and other animals, and we usually associate them with old age, although this is not always the case. Cataracts can develop due to a wide variety of factors including hereditary elements and environmental conditions, and they also come in a wide range of different types and presentations too.
Generally, cataracts can be operated on in order to retain or restore the affected dog’s vision, although this is not always possible, particularly in older dogs that will not be able to tolerate the anaesthetic and surgery safely. However, some types of cataracts are more prevalent in younger dogs than their older counterparts, and one of these is the so-called posterior polar subcapsular cataract or star cataract, which is what we will be talking about in this article.
Read on to learn more about posterior polar subcapsular cataracts or star cataracts, how they affect dogs, what sort of dogs are most prone to develop them, and what can be done about them.
The term “cataracts” refers to any condition that causes opacity or clouding of the lens of the eye, and which may affect either both eyes or just the one. Left unchecked, cataracts develop and progress to the point that they can cause blindness, but they are not painful or uncomfortable, although they do obviously compromise the dog’s vision.
Posterior polar subcapsular cataracts are just one of the many different types of cataracts that can present in the dog, and this type of cataract has a very distinctive appearance by presenting with an irregular-looking development of opacity on the surface of the eye, which is white or light in colour and which can look like a distant galaxy in shape, in comparison to the more common even opacity that appears in most forms of cataracts.
Posterior polar subcapsular cataracts tend to have a more acute effect on the dog’s vision when fully developed than other types of cataracts, but they are also usually quite slow-growing and often, take a long time to really affect the dog’s eyesight.
Posterior polar subcapsular cataracts are a type of hereditary cataract, which means that if other dogs within your dog’s breed line or ancestry have or have had star cataracts themselves, there is a higher chance of your own dog developing the condition.
Also, star cataracts tend to appear much earlier in the dog’s life than most forms of cataracts, with the average age of affected dogs being 6-18 months old. Posterior polar subcapsular cataracts in dogs can even appear as early as six to eight weeks of age, but may not develop in other dogs until they are nearer six or seven years old. Generally, star cataracts will affect both eyes, developing simultaneously at around the same rate of growth and development.
Because posterior polar subcapsular cataract development is hereditary in nature, they are much more common in a small number of breeds of dog than others, including the Rottweiler, Labrador retriever and golden retriever. It is important to note that this information is specific to posterior polar subcapsular cataracts only, and many other dog breeds have a hereditary predisposition to other types of cataracts, which should be borne in mind.
As mentioned, posterior polar subcapsular cataracts are hereditary in nature, although the exact mode of heredity is not fully understood and as such, it is not possible to health-test dogs of affected breeds prior to breeding, other than by means of generalised DNA testing for eye problems and more mainstream forms of cataracts.
Research and study into posterior polar subcapsular cataracts in dogs is not particularly well funded or comprehensive due to the comparative rarity of the condition, but star cataracts are most widely considered to be caused by a dominant hereditary trait with incomplete penetrance, which is explained as follows:
A dominant trait is one that tends to become prevalent within the breed line over time, because in order for a dog to have said trait themselves, they only need to inherit the gene responsible for it from one parent and not both. However, incomplete penetrance means that there are some exceptions to this rule, and it is possible that even if a dog inherits the dominant trait in question, they will not express-or display-the trait.
That said, one should not rely upon the incomplete penetrance element of the dominant trait for posterior polar subcapsular cataracts to negate the condition-the nature of the dominant trait itself still means that there is a high probability of inheritance if just one parent had the condition.
Like most types of cataracts, star cataracts in dogs can generally be successfully removed with surgery, restoring normal vision. There is always a chance that cataracts will re-grow again in the future-particularly given that star cataracts often appear early in life-but surgery will restore the dog’s vision if it begins to fail, and help to maintain their quality of life.
Dogs that have had a posterior polar subcapsular cataract should not be used for breeding, because of the strong probability that they will pass the condition on to their own offspring.