Characterization and prevalence of cataracts in Labrador Retrievers in The Netherlands. 
To assess the prevalence and distribution of types of cataract, investigate the effects of selective breeding on cataract development, and identify the relationship between posterior polar cataract and other types of cortical cataracts in Labrador Retrievers in The Netherlands.  9,017 Labrador Retrievers.  Records of 18,283 ophthalmic examinations performed by veterinary ophthalmologists from 1977 through 2005 were reviewed.  There were 522 dogs affected by hereditary cataracts in 1 or both eyes without progressive retinal atrophy (PRA) and 166 PRA-affected dogs with cataracts.  These cataracts were divided into 3 groups: posterior polar (triangular) cataract, extensive immature and mature cataract, and a miscellaneous group.  Dogs with PRA were analyzed separately.  From 1980 through 2000, the prevalence of hereditary cataracts was stable at 8%.  The prevalence of cataracts in offspring of cataract-affected dogs was significantly increased, compared with the prevalence in offspring of nonaffected dogs.  The distribution of types of cataract was significantly different between dogs with primary cataracts and PRA-affected dogs.  Dogs with posterior polar (triangular) cataracts produced affected offspring with the same distribution of types of cataracts as the entire population of primary cataract-affected dogs.  Cataract development in the Labrador Retriever population in The Netherlands appears to be a predominantly genetic disorder.  Posterior polar (triangular) cataracts appear to be related to other types of hereditary cataract.  Although there is no conclusive evidence, it seems valid to continue exclusion of all Labrador Retrievers affected by any type of primary cataract from breeding.