| Description:
|
Canine Progressive
Retinal Atrophy (PRA) refers to a broad group of inherited,
and sometimes acquired, retinal conditions which will
eventually result in the blindness of the dog. Due to
the nature of this disorder, and the fact that it does
not always have noticeable symptoms until it is relatively
advanced, repeated examinations might be required to
detect the animal with PRA. Dogs that have been affected
and diagnosed with Progressive Retinal Atrophy should not be used for breeding
purposes. Should the dog be fighting a viral or bacterial
infection, it will be reflected in the general health
of the animal's eyes. The eye, particularly the retina,
is dependant on a supply of blood to keep it fed and
healthy. If the blood supply becomes contaminated with
a virus, bacteria or toxin, the eyes are like windows
to the state of the body, and changes within the eye
can be observed and these are often important in making
a diagnosis of an illness. The retina is a highly complicated
tissue located at the back of the eye. Light strikes
the retina and starts a series of chemical reactions
that causes an impulse. The impulse passes through the
layers of the retina to the optic nerve, and from there
to the brain where vision takes place. In the retina,
cells called rods are involved with black and white,
or night vision. The cells called cones are involved
with color, or day vision. Progressive retinal degeneration
may affect the rods alone, the cones alone, or both
the rods and cones together. Progressive Retinal Atrophy should not be confused
with dysplasia which is a blindness caused by the abnormal
development of the retina. Progressive Retinal Atrophy
is the slow death of retinal tissue and the owner may
overlook the earliest signs. PRA is not a painful condition
- there are neither reddened eyes nor any increase in
blinking or squinting. Sometimes what happens is the
owners may notice an abnormal "shine" coming
from their pet's eyes. This abnormal shine occurs because
the pupils are dilated and don't respond as quickly
to light as the pupils of a normal dog. Some dogs will
seem disoriented when going out to the yard at night;
the owners end up leaving a light on for them. Night
blindness may be observed in a dog that is afraid to
go into a dark room. Occasionally, these dogs will get
lost in their own home after the lights have been turned
off. Night vision difficulties, in most cases, will
progress to day blindness as well. |
| Inheritance: |
Canine Progressive
Retinal Atrophy shows an autosomal recessive mode of
inheritance; therefore two copies of the defective gene,
one inherited from each parent, have to be present for
a dog to be affected by the disease. Dogs with one copy
of the defective gene and one copy of the normal gene
- called carriers - show no symptoms but can pass the
defective gene onto their offspring. |
