When the bottom of the white part of the eye, known as the sclera, is visible it is referred to as'Yin Sanpaku' in Chinese lore. According to the myth, it represents physical imbalance in the body and is claimed to be present in alcoholics, drug addicts and people who over consume sugar or grain. Conversely when the upper sclera is visible this is called 'Yang Sanpaku'. This is said to be an ndication of mental imbalance in people such as psychotics, murderers, and anyone rageful. Stress and fatigue may also be a cause.
http://en.m.wikipedia.org/wiki/Sanpaku