Notice that the iris is not a solid tone, but has streaks of color, dark around the edge. Observe your subject carefully to identify the patterns of their iris, and note highlights and reflections on the surface of the eye, which alter their appearance.
At this angle, the inside rim of the lower eyelid is visible, and part of the upper. Often a broken line is used when drawing the lower eyelid, to indicate this lightness, or in a tonal drawing, there may be a highlight.
The 'whites' aren't really white. They have slight color and often visible blood vessels, and are frequently shadowed. Reserve pure white for highlights.