Although Vanderpoel's book isn't necessarily a how-to-draw-it book, it goes into great detail about the anatomy of the eye, as well as the structure of the eye socket and the muscles that surround the "orbit" as he calls it. As Mark pointed out, understanding Vanderpoel's descriptions sometimes requires multiple readings, but it's well worth it. He wants the reader to be able to visualize not just the physical aspects of the eye structure, but how shadow and light affect its appearance. Reading this was a little bit like reading philosophy in college - I'd read a passage over and over until I fully understood it. Believe me, it opened my eyes, so to speak.
Here are some eye studies based on Vanderpoel's drawings.
