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
Eodiscina surface. The interlensar sclera is not deeper than the lenses. This type of eye is called abatochroal. A second type of eye, called schizochroal, is unique to the Phacopina suborder, and has up to several hundreds of relatively large lenses (0.05-0.5 mm), that do not touch either, but the corneal membrane extends into the sclera outside the lens, and the sclera is deeper than the lens. The most usual type of trilobite eye, called holochroal, has usually thousands of small hexagonal lenses without an interlensar sclera, and a common cornea. Many later Eodiscina however, lost their visual organs altogether, and