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become evident as late as ten years of age or even
later. Most common is rod dystrophy with subsequent affection of the cones. Initial signs are nyctalopia, tunnel vision, insecurity under dark conditions etc. The end- result is complete blindness. Funduscopically there is
an initial thinning of the retinal vessels, with subsequent tapetal hyper-re ectivity and pallor of the optic nerve head. Secondary cataracts are not uncommon. The cone-rod dystrophy is characterized by an initial
affection of the cones with a subsequent affection of
the rods. Initial symptoms are photophobia, blindness in bright light, miotic pupils etc. Later in the course of the disease, the rods are affected and the animal becomes completely blind. Funduscopic changes are similar to those of rod-cone dystrophies. In cone dystrophies the clinical symptoms are similar to the initial symptoms seen in cone-rod dystrophies, but rod-function usually remains normal. Funduscopically there are no obvious changes. ERG can be used to con rm the diagnosis of rod-cone, cone-rod and cone dystrophies often before clinical signs are evident. Differential diagnoses are chorioretinis, post in ammatory, sudden acquired retinal degeneration (SARDS), toxic retinopathy etc. Several gene-tests
are available for speci c photoreceptor dysplasias/ degenerations (www.optigen.com, www.aht.org).
Optic nerve head (ONH) aplasia/hypoplasia/ micropapilla: ONH smaller than normal or absent. Animals with ONH-aplasia are blind from birth, whereas animals with hypoplasia have visual affection or are blind. A sequelae is retinal detachment. In animals with micropapilla there is no evidence of abnormal vision. Differential diagnosis is ONH-atrophy.
Suggested reading:
Veterinary Ophthalmology, 5th ed, Gelatt et al., Wiley Blackwell.
Slatter’s Fundamentals of Veterinary Ophthalmology, 4th ed, Maggs et al., Saunders
An Urban Experience
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