What clinical signs are visible in this polydypsic polyuric twelve year old male neutered Yorshire Terrier which has become blind over a few days. Can you explain its sudden loss of sight and what treatment could restore vision?
The dog has a mature cataract with evidence of water clefts. These total lens opacities are seen in diabetes mellitus in the dog where the buildup of the insoluble glucose metabolite sorbitol can suddenly caus an osmotic cataract, hence the rapid loss of vision in this dog. Other signs include iris atrophy, seen as polycoria (multiple small holes in the iris appearing as ‘many pupils’. The iris is somewhat dark which may indicate developing lens induced uveitis. The diabetic cataract is intumescent, that is to say enlarged in size (Williams DL: Lens morphometry determined by B-mode ultrasonography of the normal and cataractous canine lens. Vet Ophthalmol. 2004 7:91-5) and microfractures in the lens capsule allow lens protein into the aqueous humour, elliciting an inflammatory reaction with iridal darkening. Such change worsens the prognosis for a successful surgery to remove the cataract, but this is the only treatment option which will restore vision after diabetes has been stabilised.