Canine Hip Dysplasia is observed in all breeds with an adult weight greater than 35 pounds. The problem is in the development of the boney structures of the hip joint. In normal hip joints the femur (thigh bone) sits solidly in the acetabulum (cup of the pelvic bones). In hip dysplasia, loose ligaments allow the head of the femur to begin to work free as the puppy grows. Because of this joint laxity, there is abnormal wear and tear on the boney surfaces that touch resulting in the development of arthritis. This arthritis results in varying degrees of symptoms including pain and restricted movement. 

The Orthopedic Foundation for Animals (OFA) will certify the X-rays of breeding dogs as normal and issue a certification number. The dog must be at least 2 years old to obtain an OFA certification. Ask to see these documents on both parents before purchasing a puppy. 

Further reading: Hip Dysplasia (CHD) by Jack Vanderwyk 

Retinal Diseases 
The retina is a membrane which lines the back of the eye and contains the light receptors needed for vision. Progressive Retinal Atrophy (PRA) and Central Progressive Retinal Atrophy (CPRA) are diseases which progressively destroy these light receptors resulting in gradual loss of vision and blindness. Both PRA and CPRA are inherited conditions and have been documented in several breeds including Labrador Retrievers. Any dog having one of these diseases is capable of transmitting the disease to his offspring if mated with a dog carrying the trait for the disease. Fortunately, a simple eye examination at the proper age will diagnosis the condition. Reputable and informed breeders have their breeding dogs examined and certified through the Canine Eye Registry Foundation, Inc. (CERF) Ask to see the CERF certification on both parents of the litter before purchasing a puppy. 

Retinal dysplasia involves abnormal development of several structures of the visual system. Dogs may be very mildly affected and demonstrate folds in the retina. These are areas where extra retina develops and instead of forming a thin membrane over the back surface of the eye, the extra retina develops into folds. This fold results in a blind spot. Often times the retina is also undernourished and an area of retinal degeneration will occur. Dogs with mild changes (i.e. a few retinal folds), usually have no 
visual compromise. Subtle changes on the part of the dog, on the positioning of the head while marking a bird, help affected Labradors make use of normal areas of the retina. Larger blind spots may cause dogs to miss a mark or miss stationary objects, while these dogs are able to perceive moving objects with less difficulty. 

Labradors with a more severe form of retinal dysplasia may result in blindness due to large areas of retinal folds or degeneration. Retinal detachment can also develop resulting in blindness. The more severe form of retinal dysplasia can occur with retinal separation, cataracts, and eye enlargement in dogs which inherit the gene from both the bitch and stud dogs. These dogs also may suffer from skeletal dysplasia or dwarfism, as the same gene for retinal dysplasia (which works in a dominant fashion for the eyes) cause skeletal dysplasia (in a recessive fashion). 

Further reading: Dwarfism by Jack Vanderwyk 

Source: Dog Owners Home Veterinary Handbook, Delbert Carlson, DVM and James Giffin, MD