The first thing to note is the 'window' of light on the eye. Effective drawings of eyes
almost always contain a light spot near the iris, where the light hits. Keep in mind that
the eyeballs are not flat, but they are spherical and therefore require shading in the
corners of the eyeball. Also, the top of the eyeball is usually darker than the bottom
because of the shadow created by a higher light source and the eyelid.
As for the iris, its edges are darker than the interior. However the dark area is not
simply an outline but involves a series of lines blended toward the interior. The pupil is
the darkest area on the eye. When shading, start with that first.
Make sure that there is shading near the eyelid. The part where the eyes
fold in is another dark part of the eye. This area goes deeper into the face so it will be
lighter than the skin around the eyebrows. There should be thickness to the lower eye
line, which is lighter than the area around it. Make sure that the shading for the 'bags'
below the eyes are well blended, for they could alter the age appearance of your subject.
Last, but not least, the eyebrows and eyelashes are hairs, and should be
done with a sharp pencil. Line the top of the eye before adding the eyelashes. Use single,
quick strokes outward for each lash, and try to make it come to a point at the tip. The
eyebrows should be shaded in lightly, with a layer of short strokes on top.
The closed eye has a different approach than a regular eye. The eyelid covers an area
that is curved, so the shadow from the side will curve inwards before blending in with the
lighter areas. In certain situations, the light will hit the eyelashes creating a curved,
light area.