It is often said that the eyes are the windows to the soul. Certainly, many people feel uncomfortable looking directly into another person's eyes and the recipient of such a stare can feel equally uncomfortable. This has led to striking differences between societies. In the West, being able to look someone in the eyes is taken as a sign of honesty. In the East however, this is seen as a challenge and regarded as intimidatory.

But there can be good medical reasons for looking someone in the eyes. There are indicators in the eyes that can, it is said, show the mental and physical well-being of the subject.

The Japanese have a word for it, 'Sanpakugan' or 'three whites' eyes, often shortened to 'Sanpaku'. The amount of white, or sclera, that is visible when someone is looking straight ahead can say a lot. When a baby is born the coloured part of the eye, the iris, is neatly centred between the upper and lower eyelids with the sclera only visible at the sides. This indicates that the baby is unstressed and in good physical condition.

But there are states of ill-health less severe than death that may cause the lower or upper sclera to become visible. Traditional Chinese medicine and homeopathy relies heavily on assessing visible often seemingly unrelated symptoms. When the lower sclera is visible, this is called 'Yin Sanpaku' and is attributed to physical imbalances in the body. Drug addicts, alcoholics and people who eat too much sugar or grain may exhibit 'Yin Sanpaku'. 'Yang Sanpaku' is where the upper sclera is visible and is sometimes indicative of mental imbalance. Psychotics, murderers, and people generally filled with rage are said to be liable to exhibit 'Yang Sanpaku'. However, stress and fatigue may also cause this symptom.

Famous people who exhibited Sanpaku eyes at various points in their lives were John F Kennedy, Marilyn Monroe and particularly Abraham Lincoln, who can be seen exhibiting Yin Sanpaku in this famous postcard.