Sanpaku (literally "three whites" in Japanese), is a term used in traditional Japanese physiognomy to describe a person with eyes where the whites of their eyes are not only visible to the right and the left of their iris, but also under their iris, between the iris and the lower eyelid (hence, "three whites"). Traditionally this was held to be a sign of spiritual or physiological imbalance, and was also said to be a sign of future bad luck.
The term "sanpaku," often expanded to "sanpaku eyes" in English, was first popularized in the West in the 1960s by Japanese health guru George Ohsawa, the founder of the philosophy of "macrobiotics." Ohsawa made much of the fact that famous people such as John F. Kennedy, Marilyn Monroe, and Abraham Lincoln had sanpaku eyes in an effort to claim that their "unbalanced" lifestyles, which could be seen in their sanpaku eyes, led to their untimely demises. They could have saved themselves, Ohsawa implied, if only they had followed his philosophy of macrobiotics and embraced the "macrobiotic diet" he was advocating. Doing this, Ohsawa argued, would have both eliminated their sanpaku eyes and altered their fates.
Although obviously not called "sanpaku," the phenomenon of the whites of the eyes being visible below the iris was also viewed negatively in Western traditions of physiognomy. Cesare Lombroso, for example, the 19th century Italian inventor of "Criminal Anthropology," who argued that criminal tendencies were genetically inherited from parents and could be recognized by physical signs, particularly in a person's face, associated the whites of the eyes being visible below the iris with the "criminal tendency to squint."
It goes pretty much without saying, however, that the idea that "sanpaku eyes" have any connection with physical or psychological imbalances, bad luck, or criminal tendencies is totally rejected by modern medicine and science.