From Wikipedia: Sanpaku gan or sanpaku is a Japanese term meaning "three whites". It was introduced into English by George Ohsawa in the mid-1960s. It is generally referred to in English as "sanpaku eyes" and refers to eyes in which either the white space above or below the iris is revealed.

This eye pose gives an impression of intense, complex or unstable emotion. Depending on whether the sclera are visible above or below the eye, It can make a character appear solemn or severe(below) or insane(above.) Famous examples of these include John F. Kennedy and Charles Manson, respectively. It can be caused by medical conditions, head posture, height differences, or even be trained as a skill- thus it's important to limit judgements made based on it and disregard the pseudoscience of physiognomy attached to the word's history. The effect is greatly reduced as a characters' eyes become less realistic as in conjoined_eyes.

Often overlaps with sad_eyes, angry_eyes or surprised_eyes; as well as looking_up or looking_down relative to the viewer.

It is distinct from eyes_rolling_back, dead_eyes, or fucked_silly, where a physical condition(e.g. an orgasm or a seizure) forces more than two whites to show.

For images where the sclera is visible all the way around the eye, consider soul_devouring_eyes, bulging_eyes or crazy_eyes.