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. Homozygous merles can be deaf or blind, or express iris colobomas, retinal detachment, cataracts, persistent pupillary membrane, a displacement of the lens, equatorial staphyloma, night blindness and microphthalmia. Audio impairment or deafness usually develops after the birth of a puppy with their ear canal still closed. The white color of double merles is produced due to the lack of melanocytes which provide high potassium levels in the endolymph surrounding the cochlea's hair cells. There is no surgery or treatment that can reduce the damage. Loss of hearing is directly linked to the amount of pigmentation cells a dog has.
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