Optic nerve hypoplasia
This disease can occur either as an isolated unilateral or bilateral ocular anomaly or as a component of the syndrome of septo-optic dysplasia, which has evolved to include microphthalmia, retinal dysplasia, retinal detachment, midline brain malformations, hydrocephalus and hypopituitarism.
Optic nerve hypoplasia is thought to be inherited in Miniature Poodles and has been seen occasionally in several canine breeds, including Beagle, Dachshund, German Shepherd, Miniature Schnauzer, Rough Coated Collie, St. Bernard, Bouvier des Flandres, Pekingese, Belgian Sheepdog, Miniature and Toy Poodle, Russian Wolfhound, Tervuren, English Cocker Spaniel, and Pyrenean Mountain Dog.
Clinically affected dogs present at a young age with ipsilateral or bilateral mydriasis, blindness, menace deficit, and absent direct pupillary reflex, but with a normal consensual reflex in the affected eye following stimulation of the normal eye. The pupils of the affected eyes will not respond quickly, if at all, to light. When light is shone into the eyes, the normal reduction in pupil size does not occur. When examined closely, the pupils will appear to be excessively dilated. In some cases, the dog may develop cataracts.
Diagnosis is suggested by a history of visual impairment from birth and clinical findings.
A definitive diagnosis requires histological evaluation of the optic nerve, showing vacuolation and a general paucity of neurons in ganglion cells of the retina. The optic nerve foramen/canal may be markedly narrowed in some affected animals.
The prognosis is poor in most cases and there is no treatment.
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