Intercanthal distance

Intercanthal distance is the distance between the inner corners of the two eyes. It is most usefully expressed relative to the width of one eye rather than in millimetres, because the ratio does not change with how close the camera was: the classical convention is that the two should be equal, so the eyes sit one eye-width apart, giving a target of 1.0. Real faces spread on both sides of it. A broader nasal root — the anthropometric norm across much of the world — produces a larger ratio, which a rule written from a European drawing convention reads as wide-set. Neither direction is associated with anything beyond how the face gets described. The measurement is unusually stable: unlike jaw width or fWHR it barely moves with weight, expression or age, which makes it comparable between photographs taken years apart.