Eyes may just be some of the trickiest parts of the human body you can draw, and, especially when it comes to realistic eyes, this may discourage you. You have to keep trying though, because getting the hang of drawing eyes means that you will also learn...

This video shows how to draw a realistic looking eye. It starts off looking simple, but then shows how, with some simple techniques, you can really get the drawing to look very realistic. http://www.youtube.com/watch?v=DkeF7gfyM-U