The Australian Shepherd, often known simply as the 'Aussie', is a medium-sized breed of dog that was, despite its name, developed on ranches in the United States during the 19th century. There is disagreement regarding the exact history of the breed prior to its arrival in the United States, and thus no official consensus on the origin of its name or association with Australia. Also, great variety is seen in the Aussie's eye color, and they are often heterochromatic. Also, great variety is seen in the Aussie's eye color, and they are often heterochromatic. An early nickname for the breed was 'ghost-eye dog'. Merled eyes occur, as well, where one color is mixed in and swirled with another. Any combination of eye color is acceptable in the breed standard, so long as the eyes are healthy. Merled eyes occur, as well, where one color is mixed in and swirled with another. Any combination of eye color is acceptable in the breed standard, so long as the eyes are healthy.