The retina is a structure in the back of the eye. It is responsible for receiving light through the lens and converting it into electric signals that can be transmitted to the brain and perceived as sensory data. It is quite a complex instrument, and as such, malformations can occur during its development. These are rare problems, but certain factors such as the breed of your dog and certain matters of heredity can affect the likelihood of contracting them.
Retinal dysplasia is a disorder that occurs when the two layers of the retina do not form together in the correct manner during the formation of the fetus. In its mildest form, this causes light accordion-style folding to occur on the inner layer of the retina, which are called "retinal folds". This disorder is not progressive, which means that whatever degree of severity a puppy possesses at birth is as severe as the disease will ever get.
Retinal folds can be detected in puppies as early as six to eight weeks with the aid of veterinary instruments such as lights and ophthalmoscopes, but checking them again at maturity can help to provide a more accurate reading. This is because the eye has a larger surface area, allowing you to see things in greater detail, and older dogs generally move around a lot less than puppies, affording you a clearer view.
Retinal folding can affect any breed, but those most likely to be born with it include Akitas, Spaniels of all types, Shepherds of all types, Labrador Retrievers, Rottweilers, and Terriers. Factors that affect its inheritance are generally not very well understood, but in both the Samoyed and the Labrador, there is a distinct link between certain skeletal defects and retinal folding.
Mild retinal folds don't usually cause significant vision problems, but they may create very small blind spots. It's very likely that your dog will never even notice these. The greater the number of folds, however, the less surface contact there is between the two layers of the retina, and the greater risk there is for retinal detachment. When and if retinal detachment occurs, total blindness is the result, and the situation cannot be reversed.
Like most problems with the eye, there is no real treatment for retinal folds, so it's fortunate that they're usually not a serious problem. There has been some research into surgeries that might repair more serious folding, but as of yet nothing is very solid or readily available.
Since retinal folding is known to be a congenital problem, it is not recommended that you breed a dog that carries it or has close relatives who do.