Retinal Dysplasia


The BTHG acknowledges the help received from Stuart Ellis, (MRCVS ), a panellist for the BVA/KC/ISDC, in the preparation of this note.



Introduction.


The back of the eye is lined with a layer of retinal cells which are stimulated by light passing into the eye through the lens.  This information is converted into nerve impulses which are conveyed via the optic nerve to the brain where they are interpreted as visual images.


There are several forms of Retinal Dysplasia, differentiated on the basis of the changes in the structure of the retina.  In the Bedlington terrier the main change is that the retina becomes detached from the underlying membrane.  This is classed as a Total Retinal Dyspasia (TRD).



Symptoms.


There are no specific symptoms.  Young puppies are naturally ungainly and unsteady on their legs.  They will constantly bump into things but as they get older they rapidly develop more control over their movements.


However, visually impaired puppies generally appear to be less active and to collide more frequently with objects. This is particularly noticeable when first introduced to unfamiliar surroundings, e.g. when they are moved from the confines of a whelping box or pen.



Diagnosis.


The condition can be readily diagnosed by examination of the eyes with an ophthalmoscope.  TRD is present from birth and can therefore be detected as soon as the eyes are fully open.



Treatment.


There is no treatment for retinal dysplasia.



Mode of Inheritance.


In Bedlingtons total retinal dysplasia is due to an autosomal recessive mutation and in order to develop the condition the dog must inherit a copy of the mutant gene from both parents – a dog with only one copy of the defective gene, i.e. a carrier, will not develop the condition and will appear normal.


Since it is not possible to identify carriers by means of any test that is currently available, it is strongly advised that parents and siblings of affected dogs should not be used for breeding.



Note.


It is a requirement of membership of the KC Assured Breeders Scheme that the parents of Bedlington terrier puppies registered under the scheme have been tested “clear” for Retinal Dysplasia.  Details of this scheme can be found at:


www.thekennelclub.org.uk/assuredbreederscheme


Note: The change to the eye testing requirement.


Until recently it was a requirement that litters of Bedlington puppies could only be registered under the KC Assured Breeders Scheme if both parents had tested “clear” of TRD within the 2 years prior to the application for registration.


The Health Group made representations to the Kennel Club requesting that, in view of the nature of the condition, this requirement be changed to a single “one-off” test thereby removing the need for possible further testing of breeding stock.


The Kennel Club acceded to the Health Group’s request and the change has now been implemented.






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Eye Conditions


Introduction.


The function of the lens is to focus light onto the retina.  A cataract may be defined as “any opacity or loss of transparency of the lens”.  Cataracts occur as a result of changes in the proteins in lens – these “coagulate” to form cloudy/opaque areas in place of the normally transparent tissues resulting in a reduction in the amount of light being transmitted and a consequential reduction in vision.  On occasions, calcium salts may be deposited within the “coagulated proteins” which results in further impairment of vision.



Types of Cataract.


Most types of cataract are inherited but some, non-hereditary cataracts are the consequence of other factors, e.g. injury, disease, physiological changes etc.


Cataracts can vary considerably in size, in their position on the lens and in their opacity, i.e. on the degree to which they impair vision.  However, they are usually categorised primarily on the basis of when they develop.





The Cambridge University Database of Canine Inherited Diseases indicates that in Bedlington terriers the cataracts are an early onset (juvenile) type with a variable pattern of progression and can be detected from about 2 months of age.  The cataracts usually develop in the posterior sub-capsular region and one or both eyes may be affected.



Symptoms.


In the early stages there may be very little indication that anything is wrong, particularly if the cataract is small and at the periphery of the lens.  It may be that the first indication is that the owner notices some discolouration of the pupil(s), i.e. a grey opaqueness.



Diagnosis.


The condition can be readily diagnosed by examination of the eyes with an ophthalmoscope.  



Treatment.


In many cases the presence of cataracts does not seem to restrict the dog’s vision to such an extent that its quality of life is significantly affected.  However, if necessary, it is possible to have cataracts removed surgically. Before deciding on this course of action, the matter should be fully discussed with your veterinary surgeon.



Mode of Inheritance.


In Bedlingtons juvenile cataracts are due to an autosomal recessive mutation and in order to develop the condition the dog must inherit a copy of the mutant gene from both parents – a dog with only one copy of the defective gene, i.e. a carrier, will not develop the condition and will appear normal.


Since it is not possible to identify carriers by means of any test that is currently available, it is strongly advised that parents and siblings of affected dogs should not be used for breeding.






Cataracts

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