The Golden Retriever is a medium-large gun dog that was bred to retrieve shot waterfowl, such as ducks and upland game birds, during hunting and shooting parties. The eyes are round and dark, which is in contrast to the triangular or slanted composition of their American counterparts. British Golden Retrievers can have a coat colour of any shade of gold or cream; red or mahogany are not permitted. Eye diseases are also possible in the breed; cataracts are the most common eye disease, but they can also be afflicted with progressive retinal atrophy, glaucoma, distichiasis, entropion, corneal dystrophy, and retinal dysplasia.