Its not that your sketches are bad, at all. but, I wholeheartedly second (& Third) Carl's Suggestion on DaVinci's Anatomy studies or any anatomy for the artist type books. And, when those are not appealing or available....draw from life as DaVinci did. Sketch Real people either in person, or from photos. Sketch all shapes and expressions to get a real feel for the anatomy behind the eye, and the orbital bone structure that makes up the shapes that surround it and hold it in place. They do not have to be posed. Eventually you will develop the muscle memory (so to speak) of the base forms and then focus on details. I try to sketch quickly things that are passing, so that I it trains the eye to pick out the details and capture them. Its OK to draw from the minds eye, but to truly know the body part (eye in this case), Study it! I would also suggest, sketch in less permanent mediums initially... INK is good, but is less forgiving if you add something you don't like later. All in all, you are on the right track, practice, keep it up... Don't feel its "less" to review a reference material. You are doing great and cant wait to see more.

Sketch ya later.