Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best. Management
There is no treatment for PRA. However, most dogs that suffer from this disease adjust remarkably well. To maximize the quality of the dogs life,  follow these guidelines:

Do not rearrange furniture, as the dog has memorized the layout of the environment
Use a short leash when walking a dog with blindness from advanced PRA
Erect safety barriers around pools or balconies

See also
Sudden acquired retinal degeneration

References
External links
Article on PRA
Article on Cataracts
Isodicentric 15, also called marker chromosome 15 syndrome, idic(15), partial tetrasomy 15q, or inverted duplication 15 (inv dup 15), is a chromosome abnormality in which a child is born with extra genetic material from chromosome 15. People with idic(15) are typically born with 47 chromosomes in their body cells, instead of the normal 46. The extra chromosome, which is classified as a small supernumerary marker chromosome, is made up of a piece of chromosome 15 that has been duplicated end-to-end like a mirror image. It is the presence of this extra genetic material that is thought to account for the symptoms seen in some people with idic(15). Individuals with idic(15) have a total of four copies of this chromosome 15 region instead of the usual two copies (1 copy each on the maternal and paternal chromosomes). The syndrome is also often referred to by the term Chromosome 15q11.2-q13.1 Duplication Syndrome, shortened to Dup15q Syndrome, or marker chromosome 15 syndrome (mainly in the United States). Dup15q Syndrome includes both idic(15) and interstitial 15q11.2-q13.1, another type of duplication that causes similar clinical traits. The extra chromosome is occasionally found in the mosaic state, i.e. some of the cells carry the marker chromosome. However, mostly because of the markers instability and tendency to be lost during cell division (mitosis), some cells are completely normal with 46 chromosomes. Occasionally, cells may have more than one idic(15), resulting in 48 or 49 chromosomes in all or some of their cells.