Retinal DysplasiaThis has been diagnosed in several corgis and a subtype, retinal folds, can be seen in dogs who have been CERF-examined*.
Retinal dysplasia is a type of retinal malformation. The word "dysplasia" simply means "a defective development of an organ or structure". Retinal dysplasia occurs when the 2 primitive layers of the retina do not form together properly.
The cause of retinal dysplasia in most breeds is genetic although prenatal infections with herpesvirus and parvovirus may also lead to it.
Mild dysplasia manifests as folds in the inner retinal layer. These are called "retinal folds". Retinal folds rarely cause vision problems for the individual dog. They represent small blind spots which are probably not even noticed by the dog.
In "geographic" retinal dysplasia, however, there are larger areas of defective retinal development. In the severe form of dysplasia, the 2 retinal layers do not come together at all and retinal detachment occurs. Large areas of dysplasia may lead to large deficits in the visual field and dogs with retinal detachments are completely blind.
Retinal dysplasia is not progressive. It is a congenital defect and animals are born with as severe a condition as they will ever get. When seen in puppies, this condition may partially or completely resolve with maturity.
Retinal dysplasia can be detected as early as 6-8 weeks on a CERF examination. However, because the size of the eye is small and young puppies are often wiggling during examination, a 6 month recheck is recommended in order for the ophthalmologist to better see the back of the eye.
Dogs intended for breeding should have their eyes examined by a certified veterinary ophthalmologist.
Dogs affected with geographic or detached retinal dysplasia, their parents and their littermates should NOT be bred.
Breeding a dog with the mild, (multi)focal form of retinal dysplasia should be carefully evaluated, but the partner should be free of retinal dysplasia.
*) A CERF examination is only done by veterinary ophthalmologists who are board certified by the American College of Veterinary Ophthalmologists who then records his or her observations on a CERF (Canine Eye Registry Foundation) form.
In other countries, veterinary ophthalmologists who are board certified in their own country will examine the eyes for breeding soundness, and will issue a certificate following the examination.
http://www.ecvo.org/ Under "Hereditary Eye Diseases" you can find a certified examiner/panelist in your country. At the bottom there is a link to a list of diplomates/panelists in many other countries.