Nothing much has changed in the incidence of disease in Border Terriers over the past year. Health survey forms continue to trickle into the database and many thanks to those who have contributed. However a number of Border Terrier owners have asked about Hereditary Cataract (HC) in Borders.
The Border Terrier has been under investigation for many years (20 plus to my knowledge) because of a suspicion that the breed has an incidence of late onset cataracts. The evidence from the Health Survey does confirm an incidence of cataract in older borders, however, this in itself is not unusual as dogs greater than 10 years might well develop cataracts due to ageing. In the database there are 15 reports of cataract making an incidence rate of approaching 2%. However when age was taken into account the incidence rises sharply in dogs aged over 10 years.
A cataract is opacity in the lens of the eye. Classically it has a milky white appearance sitting behind the iris. It is often particularly noticeable when the whiteness is so dense the light no longer reaches the back of the eye readily and the pupil dilates showing even more of the opacity. However a careful examination of the eye at an earlier stage may show signs of a developing cataract which appears as a slight opacity, especially in bright light. Cataract is a problem as it interferes with the transmission of light to the retina at the back of the eye and therefore vision will be compromised. A dog with developing cataracts may first have problems with night vision but this will develop to full blindness over time.
Cataract can be caused by ageing and by some of the diseases of elderly dogs with diabetes being a good example. Medication and physical injury to the eye can also have a role to play. However, if the cataract is caused by an inherited defect then clearly there is something to be done by the breed to reduce or eliminate this defect if at all possible. Sounds easy in theory but there are problems in achieving this. Firstly, with late onset cataract, it is often impossible to know in individual dogs if the cause is inherited or due to ageing and/or illness. Secondly, by the time a dog is found to be suffering from late onset HC it has already been bred from and probably so have its offspring and theirs too. Thirdly, unless the inherited form can be reliably distinguished from others there is little hope of understanding the inheritance in the breed nor of identifying affected breed lines.
Thus the Border Terrier stays on the suspect list but it is not clear when or if it stands any chance of being proved to have an incidence of HC or cleared of the condition. Thus it is likely that the breed will remain on the suspect list for many years to come, a fact which will probably cause many owners of ageing borders some concern but, unless some concerted action is taken to analyse the pedigrees of dogs with suspected HC (if the pedigrees have been collected), it is unlikely to be resolved in the near future.
For breeders the advice would be to consider carefully breeding from a long line of dogs that have cataracts in their advanced years but beyond this it is difficult to offer any other constructive guidance.
Prof Steve Dean BVet Med, DVR, MRCVS
Breed Health Co-ordinator
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