The distance between the centres of the pupils of the eyes is 1/3 of the face. The space between the outer corners of the eyes, that is where the eye ends in the eye socket which contains it, thus the outer corners, is half the face.
The greatest width of the face at the line of the eyes is equal to the distance from the roots of the hair in front to the parting of the lips.
[Footnote: There are, with this section, two sketches of eyes, not reproduced here.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.