For many years there has been a known genetic link between eye defects known as "Focal Retinal Dysplasia" and skeletal abnormalities known as dwarfism. The particular combination of symptoms is mainly found in field trial strains of Labrador retrievers.
Retinal dysplasia is the most important retinal disease affecting Labrador Retrievers used for hunting and field trial work. Retinal dysplasia is a widespread inherited condition in the Labrador. During CERF clinics in Minnesota, there is a 10 to 20% incidence in the Labradors examined. Most dogs have the mild form of the disease. The condition is congenital and may or may not be associated with retinal detachment depending on the extent. (It is relatively uncommon in lines of Labradors used for conformation work.) It is important to be aware of this eye disease.
Retinal dysplasia involves abnormal development of several structures of the visual system. Dogs may be very mildly affected
and demonstrate folds in the retina. These are areas where extra retina develops and instead of forming a thin membrane over
the back surface of the eye, the extra retina develops into folds. This fold results in a blind spot. Often times the retina is also
undernourished and an area of retinal degeneration will occur. Dogs with mild changes (i.e. a few retinal folds), usually have no
visual compromise. Subtle changes on the part of the dog, on the positioning of the head while marking a bird, help affected
Labradors make use of normal areas of the retina. Larger blind spots may cause dogs to miss a mark or miss stationary objects,
while these dogs are able to perceive moving objects with less difficulty.
Labradors with a more severe form of retinal dysplasia may result in blindness due to large areas of retinal folds or
degeneration. Retinal detachment can also develop resulting in blindness. The more severe form of retinal dysplasia can occur
with retinal separation, cataracts, and eye enlargement in dogs which inherit the gene from both the bitch and stud dogs. These
dogs also may suffer from skeletal dysplasia or dwarfism, as the same gene for retinal dysplasia (which works in a dominant
fashion for the eyes) cause skeletal dysplasia (in a recessive fashion).
Retinal dysplasia in Labradors is the result of a dominant gene. Dogs with only a single dose of the genetic information usually
develops the mild form of the condition with retinal folds. These folds can be seen early in life. Because retinal dysplasia is a dominant trait for the eyes, a concentrated effort should be made by dog enthusiasts, by careful selection of dogs for breeding, who do not come from lines with the condition and by using dogs who were examined at an early age and found to be clear. Examination of a two year old dog prior to breeding does not necessarily prevent the introduction of this condition into your line of dogs because very small folds noted at an early age can "straighten out" with growth, making the condition clinically impossible to diagnose in the older dog, although the dog has genetic information to produce other dogs with mild to severe forms of retinal dysplasia. Most of the dogs that are mildly affected suffer no visual compromises and can make excellent hunting dogs or pets.
There are two forms of retinal dysplasia found in Labrador retrievers; one (Retinal Dysplasia- complete) which is found predominantly in dogs of European descent and the other (retina Dysplasia-folds) found in dogs with predominantly American field trial bloodlines. The European form is inherited as an autosomal recessive gene and only effects vision.
The American form is inherited as an incompletely dominant trait with recessive effects on the skeleton resulting in abnormalities of limb development (short-limbed dwarfism). Dogs which receive two recessive genes for this defect (one from each parent) will exhibit retinal detachment which will result in blindness; however, dogs receiving only one recessive gene for this defect (one parent contributes the recessive gene for this defect and one parent contributes the gene for normal retinal development) will develop retinal folds of a non-progressive nature and, therefore, may have normal to slightly impaired vision. In this disease, three different ocular phenotypes are present (normal, localized retinal dysplasia (retinal folds), and complete retinal detachment) and two different skeletal phenotypes are present (normal or dwarf). This is an inherited condition, whose mode of transmission is as follows: Call N the normal gene and rd the gene for retinal dysplasia.
+ N x N normal eyes, normal skeleton
+ N x rd classic symptoms, retinal folds, normal skeleton
+ rd x rd dwarfism, eye problems/blindness, skeletal problems
The gene acts as an autosomal recessive in regards to dwarfism, but acts as though it were dominant when only one parent passes on the gene to its offspring.
If we bred NN x Nrd we would expect half of the puppies to be affected the others normal. If we bred Nrd x Nrd we would expect the following:
+ 1/4 normal
+ 1/2 afflicted carriers, can be identified in puppies
+ 1/4 dwarf
that the ocular and skeletal defects are inherited together, and that the skeletal effects act as a recessive trait and the ocular effects act as an incomplete dominant trait. This implies that 1) any Labrador with any type of RD is a carrier for dwarfism, and 2) at least one of the two parents of puppies with RD is a carrier for dwarfism. Retinal folds may disappear with age, so an accurate evaluation for RD requires that puppies be evaluated, ideally between 8 and 10 weeks of age.
In mild cases of retinal dysplasia, sight is probably not affected much, if at all. In severe cases, skeletal abnormalities are present.