Hereditary Retinal Diseases

INTRODUCTION The spectrum of hereditary retinal disease in the dog is well defi ned and closely related to the intensive breeding patterns which are used in some breeds. Many retinopathies are often detected as the result of routine screening in the absence of dramatic clinical features or noticeable disturbance of sight for, while our clients may notice the painful or discoloured eye, few recognise the subtle variation in pupil size and many do not suspect sight defi ciency until it is well established. The pathognomic features of retinal disease defi ned by ophthalmoscopic examination are changes in tapetal refl ectivity and pigmentation, blood vessel congestion or attenuation, haemorrhage and retinal nonattachment. Thus, a combination of reduced tapetal refl ectivity and intraretinal haemorrhage indicates active infl ammation, whereas a zone of increased tapetal refl ectivity or a patch of reduced pigmentation signifi es post-infl ammatory degeneration. Unfortunately, retinal pathology does not automatically fl ag its cause and, as such, dilemma in diagnosis is always possible. For example, the retinal degeneration which accompanies retinal dysplasia can be confused with post-infl ammatory retinal degeneration and, without history, sudden acquired retinal degeneration (SARD) can look like progressive retinal atrophy (PRA). The range of retinopathy in the dog has been largely defi ned and new retinopathies are relatively few and far between. Central PRA appears to be a misnomer because the condition is a secondary photoreceptor degeneration due to abnormal retinal pigment epithelial activity, which appears to be governed by environmental or metabolic factors to some extent. Thus, a classical ocular diagnosis becomes an ocular feature of a condition of unspecifi ed aetiology, yet one that demonstrates breed predisposition. Sadly more canine breeds become involved in the PRA story of inherited photoreceptor degeneration. Similarly more breeds are becoming involved in retinal dysplasia; the multifocal and total forms of this condition have been joined by a geographical lesion in the Cavalier King Charles and Retriever breeds. Collie Eye Anomaly is still the commonest inherited ocular disease in dogs in the United Kingdom but its recent appearance in the Lancashire Heeler suggests that a change in nomenclature would be appropriate.