Day blindness, also known as achromatopsia, is characterised by a failure of cone cells in the retina to function properly. Cone cells are responsible for vision in bright light conditions and thus affected puppies have signs of poor vision in bright light but initially retain normal vision in low light levels.
Affected dogs lose vison in bright light conditions. However, unlike other forms of day blindness in other breeds, the DB/RD mutation eventually leads to a complete retinal degeneration and ultimately causes vision loss under all lighting conditions. Day blindness is present in puppyhood and general retinal degeneration develops around 4-5 years of age.
The mutation that causes Day Blindness/Retinal Degeneration in Standard Poodle is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Day Blindness/ Retinal Degeneration during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Day Blindness/ Retinal Degeneration as a result of this mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Day Blindness/ Retinal Degeneration should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of this mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Day Blindness/Retinal Degeneration, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.