Eyes

  • PRA
  • Cataract

Progressive retinal atrophy (PRA): PRA is a blanket term for many types of retinal diseases and it is a hereditary disease that is found in a lot of different breeds and even among wild wolves. The retina is the tissue lining the back wall of the inside of the eye and is composed of two classes of photoreceptor cells called rods and cones; the rods function in dim light, and the cones in bright light. A PRA affected dog begins to have difficulty seeing in dim light, then gradually loses the ability to see in bright light, eventually becoming completely blind. As the vision fails, the pupils become increasingly dilated, and may take on a shiny or iridescent quality. When properly trained and managed most dogs can adjust to blindness well.


Early onset and late onset PRA.

There are two groupings of PRA - early onset, and late onset. In early onset PRA poor vision in low light may be detectable shortly after birth, with total blindness occurring from 1 to 5 years. In late onset forms, night blindness occurs from 1 to 5 years, progressing to total blindness anytime after 3 years of age. Both early and late onset PRA have been found in Saarloos Wolfhond.


ERG ( Electro Retino Grafi and ophthalmoscopic examination)

ERG is a rather expensive method and it can only be done at SLU (Sveriges lantbruksuniversitet) in Uppsala, the dog is anesthetized during the examination. The resources for doing this examination are very limited so you cannot just call and make an appointment like with an ophthalmoscopic examination. Dogs are in most cases referred to this examination by an eyes specialist. Therefore ophthalmoscopic examination is the method that we are the most common here. By ophthalmoscopic examination you can see typical changes long before the dog have any problems with the vision.


Hereditary.

PRA is hereditary and is always assumed to be an autosomal recessive trait until proven otherwise. (A recessive trait requires two copies of the defective gene. An autosomal recessive trait is one in which a recessive trait is carried on a chromosome pair other than the XY sex pair.) The Siberian Husky is the only breed as yet proven to have a different mode of inheritance, and it is sex-linked. As a result, most of the PRA affected Siberian Huskies are male. An affected dog must have two copies of the defective gene. A dog with only one copy of the gene is a carrier and will never have PRA, but will be able to pass that defective gene on to approximately half its offspring.

At the present time, the only way to determine if a dog is a carrier is if one of its parents is affected, or if one of its offspring is affected. Identifying carriers is imperative in order for breeders to make informed decisions and minimize the risk of producing PRA affected dogs.

This example shows how it can look when the gene is passed on through generations and in the end result in PRA affected dogs.


PRA gene = P

Free = I

PP = PRA affected ( always pass the gene to it's offspring)

PI = PRA Carrier (don't get sick but can pass the gene to it's offspring)

II =Free from PRA (don't get sick and don't pass the gene to it's offspring)


Healthy dog mated with healthy dog ( II+II) = 100% II

Healthy dog mated with carrier ( II+PI ) = 50% II, 50% PI

Healthy dog mated with PRA affected ( II+PP ) = 100% PI

Carrier mated with carrier ( PI+PI ) = 25% PP, 50% PI, 25% II

Carrier mated with PRA affected ( PI+PP ) = 50% PP, 50% PI

PRA affected mated with PRA affected ( PP+PP ) = 100% PP


Cataract is an eye condition characterized by a clouding of the lens and it can be hereditary, acquired or a combination of both. With the word cataract you mean every type of clowding of the lens, minor or bigger. Cataracts are one of the most common health issues that affect dogs' eyes and almost all dog breeds can develop it but you'll find that some types of cataracts are more common with one breed than another. Some types of cataract is very small and don't have to impair vision. It's not only the size of the cataract that decide the effect of the vision but also the location in the lens. There are several different types, signs or symptoms and causes of cataract formation.The most common potential causes of cataracts in dogs include infection, toxin, age, other disorders, and genetic health history (IE inherited cataracts).


Congenital Cataracts.

Present at birth. Caused by infection or a toxin that formed the cataracts while in the womb. In some cases congenital cataracts can be inherited.


Developmental Cataracts (Early Onset).

Also known as Juvenile Cataracts in dogs. Develop early in the dog's life. This type can be caused by outside sources such as trauma, diabetes, infection, toxin, or they may be inherited.


Senile Cataracts (Late Onset).

Develop at 6 years or older. This type of cataracts is caused by old age. At this age, nuclear sclerosis is a common cause, and is more frequently confused for cataracts.


Inherited cataracts.

Most dog breeds are prone to certain disorders, cataracts is one of them. Inherited cataracts commonly occurs in conjunction with another ocular disease. Dogs that have cataracts in their history and pedigree should not be bred, as the pups will inherit the disorder.