By Gayle Kaye
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.
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 over 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 (CEA) can be easily checked when the puppies are 5-7 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. However, 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. These conditions may or may not be of serious nature. It depends on the size and/or where the “bulge/cupping” is located.
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.
The OptiGen Company now offers a genetic test for Collie Eye Anomaly/Choroidal Hypoplasia. This genetic test can distinguish all three genetic states - normal, carrier and affected. This test also requires a blood draw done by a Veterinarian. By the way, this test should not take the place of annual eye exams....nor does it provide information on a dog's PRA or coloboma status. Please visit the OPTIGEN website for details http://www.optigen.com/opt9_test_cea_ch.html
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 generally 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 number of affected and seriously affected Collies has been 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.
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.
“PRA”, or rod-cone dysplasia type 2 (rcd2), is a form of retinal degeneration that has been in collies for decades. In this disease, an abnormal development (dysplasia) of the rods and cones (the light sensitive cells in the eye) leads to an early onset of night blindness that is typically apparent by the time pups are 6 weeks of age. In most cases, the rcd2-Affected dog is completely blind by the time it is 1 year old.
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.
There is a simple genetic test available to determine if a dog has PRA or if it is a carrier for PRA. The rcd2 DNA test is able to identify with complete accuracy whether a dog has no copy (is Normal), has 1 copy (is a Carrier) or has 2 copies of the mutation (is Affected). Please visit this website for more information on testing: http://www.optigen.com/opt9_rcd2testpage.html