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"Your Collie's Eyes"
(Cross-section of the Canine Eye)
Like people, Dogs are subject
to a
large number of inherited eye
diseases. Two which can affect a
Collie's eyes should be of
concern to
all breeders.
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COLLIE
EYE ANOMALY
This is the most common of the Collie
eye diseases, but it should be noted
that Collies
share this disease with
several other breeds. Researchers first
noted this problem nearly fifty years
ago. It was later found to exist in most
Collies and in most Collie families. This
so-called syndrome,
meaning a group
of conditions which appear in
conjunction with each other, is present
prior to
birth. Collie Eye Anomaly can
be easily checked when the puppies
are 5-6 weeks old, by a qualified Board
Certified Ophthalmologist. It is
something that your average
Veterinarian is not qualified to
diagnose. The eyes must be dilated
prior to the examination, so the interior
of the eye can be examined
with an
Ophthalmoloscope.
A dog is either given a “Normal” or
"Affected" rating. If given
"affected" the
type of abnormality is noted. It used to
be popular to use a Grading System
and
still is being used in certain parts
of the country. Currently there is no
universal, standardized grading
system.
Normal: A “Normal” eye rating is of
course the best grading there is.
(There
are also "Go Normals", which
are so mildly affected at a young age,
that later, the pale areas disappear,
leading to what is termed a "Go
Normal". Keep in mind that these are
still in fact affected with
CEA). There
are variations even in "Normal" eyes.
These correspond somewhat to a
dog's coat color.
Thus it is often
difficult to judge the pigment in a Blue
Merle's eyes as it is diluted along with
his
coat color.
Choroidal Hypoplasia, Chorioretinal
Change:These refer to abnormalities in
the coloring
or pigmentation of the
choroid or central layer of the eye's
lining. This is the most common
abnormality
found in Collie eyes. Often
referred to as mild CRC, Grade I or
Grade II, it is the least harmful and
least severe form of CEA. Most dogs
with this eye grade function normally
with no ill-effects or loss
of vision.
Staphyloma, Coloboma, Ectasia: While
not completely synonymous, these
terms all refer
to a cupping or bulging
in the eyeball usually in the area of the
optic disc.
Vascular Disease, Tortuous
Blood
Vessels:Defects in the vessels of the
eye which are responsible for its blood
supply or "nourishment."
These may
be malformed, undersized, or even
lacking.
Retinal Detachment: Loosening or
separation
of the inmost, or retina,
layer from the wall of the eye. This may
involve a tiny area or the entire retina.
It can be either one or both eyes. The
complete detachment of the retina
results in blindness in
that eye.
There is a new Genetic Test for Collie
Eye Anomaly / Choroidal Hypoplasia.
Please visit
the OPTIGEN website for
details
Can the Collie's eyes become worse?
Might he later go blind? The
basic
answer is "No" as CEA is present prior
to birth. However, a dog born with a
severe Staphyloma
or with Vascular
Disease may later suffer loss of sight if
a detachment or severe hemorrhage
occurs.
The majority of dogs that are
slightly affected, will have perfectly
adequate eye vision throughout their
life. (Even a dog with one blind eye will
adapt perfectly well in his
surroundings.)
What
have breeders done to improve
Collie eyes? When the eye problem
was discovered more than 50 years
ago,
it was estimated that 90% of the
Collie population was afflicted with
some form of eye disease. Because
CEA has involved such a large
percentage of the breed, eradication
has been slow . Over the years,
with
selective breeding and eye checking of
breeding stock, the numbers of
affected Collies has
greatly reduced.
ALL reputable breeders eye check not
only their breeding stock, but all
puppies
that are offered for sale.
How is CEA inherited? Most of the
specialists agree that Choroidal
Hypoplasia
is carried as a simple
recessive. For a dog to show
symptoms, both parents, even if they
show no
signs themselves, must carry
a gene for the condition. Evidence
exists that some other parts of the
syndrome are inherited differently.
Staphyloma, for instance, rarely occurs
except in the presence
of Choroidal
Hypoplasia. Dogs recommended for
breeding will vary according to the
standard set
by the individual doctor.
The ideal, of course, is to eliminate all
but the clear, non-carriers, from the
breed. Please note: Even among the
dogs that examine "normal", most are
carriers of the gene. They
have a
"hidden" or recessive gene for the
condition and will transmit the gene to
half its offspring.
Two
other conditions not part of the
CEA, which can occur, should be noted:
Hypoplasia of the Optic Nerve: An
undersized nerve which is noted where
it enters the eyeball. In extreme cases,
this can cause blindness.
Corneal
Dystrophy:This condition
comes on when the dog is mature,
often during stress. Opaque spots
appear
centrally on the surface of the
cornea. (It is often confused by the
layman with cataracts which occur in
the lense.)
In the beginning there was a lack of
veterinarians trained to examine eyes.
Then
in 1972, the American Veterinary
Medical Association formed the
American College of Veterinary
Ophthalmologists
(ACVO), thus
providing specialists in the animal eye
field. The Collie Club of America
encourages
its members to have all
their puppies checked as young as
possible by a member of the ACVO.
Where
there is none in the area, the
alternative is to sell a dog contingent
on a later check. No dog should be
used for breeding until examined and
found to be above the examiner's
standard.
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PROGRESSIVE RETINAL ATROPHY
The other Collie eye problem that can
occur in rare instances is Progressive
Retinal Atrophy (PRA). Since the name
is just what it implies,
it can be a
progressive disease, that may not
appear until later in life. This is a
completely
different and unrelated
disease to CEA. As the name
indicates, PRA is a progressive
disease which
refers to retinal
degeneration. It can result in complete
blindness in one or both eyes.
However,
Collies seem to be blessed
with the fact that PRA seems to have
an early onset. Fortunately, this is an
eye disease that has largely been
eradicated thanks to breeders efforts
of test breeding potential
carriers.
Since PRA is a simple recessive gene,
it is much easier to test for than CEA.
Also, thanks
to funding of certain
grants by the Collie Health Foundation,
research is being done to locate the
genetic
markers for this disease, which
will further reduce the occurrence.
Currently there is no genetic test for
PRA, but rumor is that researchers are
very close to finding a DNA marker.
PRA has proven to be a
simple
recessive in all the breeds studied.
Again, this means that even though the
condition is
not present at birth, both
parents must be carriers. If one parent
has PRA, half the puppies may
develop
PRA, but all will be carriers for
the disease. Early signs of the problem
may be noticed by the owner as
"night
blindness." The dog has trouble seeing
in dim light and will bump things. An
expert may
detect early signs in the
eye at six months or younger.
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