My Summary of Collie Eye Anomaly in Shetland Sheepdogs
Our KC(Kennel club), BVA (British Veterinary Association) & ISDS (International Sheep Dog Society) jointly developed a scheme to find dogs affected with recognised, inherited eye diseases that should not be bred from. Puppies can be tested up to the age of 12 weeks, although earlier testing is recommended & dogs should be retested annually to find diseases that become detectable with increasing age (e.g. PRA). The ISDS introduced it's eye testing scheme ~ 20 years ago for PRA. The incidence of PRA has decreased from > 14 % to less than .25 % of those tested last year. They began testing for CEA ~ 10 years ago & the current rate of this is 1 %. The ISDS are strict in that no puppies can be registered from parents, if those parents are older than 3 years, unless the parents have passed a thorough eye exam - All dogs competing at National Sheepdog Trials and the International Sheepdog Trial are required to pass the test and be retested annually at these trials themselves......these results really show the good effect of a responsible breeding program. Our Kennel Club uses the same testing scheme, but does not place restrictions on the breeding / activities of tested dogs & the results are for informational purposes only. Having said that, the English Shetland Sheepdog Club publish a list of CEA / PRA tested clear dogs in their handbook / magazine - very useful for future breeding strategy. The KC records & publishes the results of tests involving known (certified) inherited diseases where there is enough scientific evidence to show that the condition is inherited & the mode of inheritance. Other tests are only suspected of being hereditary & are classed as being "Under investigation".
Brief Summary of our Scheme.
The BVA / KC / ISDS scheme is the only UK eye scheme giving a clear / affected certificate on a kennel club pedigree. The BVA produces procedure notes setting out rules & regulations by which the scheme operates & they appoint a list of eye panellist specialists to conduct the eye tests. Personally, we would have our litters tested at 6 - 8 weeks to get an idea of their eye status for our future breeding strategy. Testing a litter gives us (the breeders) a certificate listing the dog's name, registration number & current eye status. The litter test (conducted between 5 - 12 weeks of age) results are sent to the Kennel Club for their records, but these results are not published. We would then retest any pups that we keep for two main reasons...(1) to check for later onset eye abnormalities & (2) to have the status report published / printed on the dogs registration certificate & on those certificates of any progeny.
The BVA appoints a panel of experienced veterinary ophthalmologist who decide what breeds / conditions should be tested under this scheme. The relevant KC registration documents must be shown to the vet at the time of testing. Both the Vets (the only two in Northern Ireland) who examined our Tess were experienced, certified ophthalmologists & while one was happy to report Tess was 'clear', the other was convince she was ' mildly affected'. Incidentally, there is now only one Vet in Northern Ireland & one Vet in Eire qualified to conduct the eye test as of 1st January 2001. We are very lucky in that the NI Vet has his practice only about 25 miles from where we live.
The classical Choroidal Hypoplasia looks like a pale patch / area in the eye. This is due to a localised lack of some / all retinal & choroidal pigment in the affected region. The two eyes often appear dissimilar. The vessels may appear abnormal in size, position & number. There may also be colobomas, but retinal detachment / intraocular haemorrhage are rare so the majority of dogs with CEA show no apparent visual defect.
The main problem with Blue Merles is that they have little fundic pigment & / no tapetum (Incidentally, merle eyes tend to shine red in the dark as they have less pigment on the reflective layer at the back of the eye compared to the more usual shiny green colour!) so choroidal hypoplasia will not be obvious & indeed usually the appearance of the vessels becomes the only diagnostic feature. Hence the difficulty & occasional differing results with Blues. Having said that, I have never heard of a dispute over a Sable, but it is clinically possible.
I find the official UK explanation of how the 'Go Normal' status arises very interesting. The most common change in the eye due to CEA is choroidal hypoplasia & is most easily detected when the pup is 5 - 6 weeks of age - thus the importance of litter screening at an early age. If signs of CEA are present at this age then the dog is affected for life, but as the dog ages, these changes may become masked (sometimes even by the age of 8 weeks if mildly affected) and the dog thus appears clear, even when examined by the same panellist.. Masking (Go Normal) occurs following pigment & Tapetal development, usually during puppyhood & adolescence. Masking obscures the hypoplasia & thus the main diagnostic feature. It has been estimated that ~30 % of CEA affected dogs are go normal. The age factor is difficult as our Eye Vet will not test before 6 & preferably 7 weeks as apparently Sheltie eyes are very difficult to examine given their size. There have also been numerous cases of dogs being certified as Clear with the KC, despite an earlier test registering them as Affected. These results have now been corrected to Affected, but they caused a lot of confusion at the time.
I have to admit that £26.00 per dog, per eye test is a fairly daunting price. I'm sure the eye tests do add quite a bit to the Vet's income, but I know it is expensive to become certified over here & have the correct equipment.
Unfortunately, the incidence of CEA in Rough / Smooth Collies & Shelties is still quite high in the UK, with Border Collies being less affected. The Go Normal status is a great threat to any responsible breeding program, but personally I would consider using an affected dog / bitch if I felt their other attributes could not be found elsewhere / I considered they were the best advantage for my breeding strategy. I would ensure they were mated to a clear dog / bitch (preferably genetically clear, but currently the only way to assume a dog is clear if through large numbers of unaffected puppies - very hard for a bitch / little used stud) & would endeavour to breed only clear (although carrier) pups. An affected dog is genetically affected regardless of whether slightly or severely. It is a shame to lose a marvellous bloodline for just one factor - especially when that factor does not cause (or does so rarely as to make it highly unlikely) any apparent visual defects in the dog. Although we are trying our best to establish a CEA clear line, I would be more concerned with hip dysplasia or poor temperaments in our Shelties.
Most studies to date suggest that CEA is caused by a single autosomal recessive gene with multiple (Pleiotrophic) effects. A Norwegian Study (before 1995) showed 68 %of pups diagnosed as affected at 7 weeks were of normal appearance by 1 year old. I wonder how may go normals are wandering about with clear certificates....personally I do not believe that clear certificates should be given out for dogs over 3 months of age. Until the availability of DNA probes / markers to test the genetics status for the CEA gene and those genes with significant modifying features, we will just have to try & ensure we breed for clear lines to the best of our ability. Good Luck to us all...
Please remember it is all just educated guesses & speculation at the moment. Until a definitive test is established for CEA we are just using probabilities & theories.
I would say that it takes an extremely brave person to list their dog as genetically clear without a current DNA test. Having said that, our Kennel Club will list a dog / bitch as genetically clear if they have a certain number of clear pups with none affected. This is the main reason that very few bitches, if any, are listed as CEA clear. A typical cause of confusion would be that if a clear pup is from two clear parents / grandparents then the pup is genetically clear - misconceptions such as this could lead to dangerous assumptions being made in breeding programs. As CEA is appears to be a single recessive gene, it could lie dormant (carrier status) for many generations and come to the fore when least expected. It seems likely that CEA will be inherited the same / involve the same gene in Shelties & Collies but, despite it's name, I think a lot of Sheltie people over here have made a big attempt in the last 5 - 10 years to reduce CEA. Unfortunately, not everyone has the same views towards eradicating CEA as others. Another name that I have heard used for CEA (Collie Eye Anomaly) is SES (Sheltie Eye Syndrome)...just in case you ever come across the alternative.
***The facts & figures quoted above have been taken from BVA / ISDS or KC leaflets, published journals and private correspondence with individuals involved in CEA research / my own knowledge.***