Appaloosa occurs in several overlay patterns on one of several recognized base coat colors. There are three other distinctive, "core" characteristics: mottled skin, striped hooves, and eyes with a white sclera. Skin mottling is usually seen around the muzzle, eyes, anus, and genitalia. Striped hooves are a common trait, quite noticeable on Appaloosas, but not unique to the breed. The sclera is the part of the eye surrounding the iris; although all horses show white around the eye if the eye is rolled back, to have a readily visible white sclera with the eye in a normal position is a distinctive
Book of the Ten Treatises of the Eye means for medieval ophthalmologists in the West to come into contact with the work of Galen. There are four essential doctrines that shape Hunayn's dissertation on vision and the anatomy of the eye: Hunayn relies on these principles to build up his conception of vision, which incorporates the anatomy of the eye in a way that makes discussion of one without the other unproductive. The structure of the eye is presented as a hierarchy, starting first with the part that is most directly responsible for sight, and working down towards the parts which exists only to facilitate this function. The