Dogs with PRA usually develop cataracts that are termed âtoxic cataractsâ, in the mid to late stages of PRA. Cataracts are opacities within the lens, and usually both eyes of dogs with PRA develop cataracts. There are many causes of toxic cataracts, but the most common cause in dogs is PRA. As the retinal tissue slowly dies, it releases toxic by-products of cell death that are absorbed by the lens, causing lens damage and cataract development.