Finally, someone who actually put effort into getting the shape of an eye :). Okay, onto c & c!
The tear duct could be more shimmery to make it look more natural as opposed to a stiff-plastic duct (remember, just because it's not in a reference, doesn't mean you can't use the artist's touch). Don't be afaid to define more of the creases below the eyes, but pay attention to how thick they are, and their exact placement. Another thing you might look at is the ends of the iris as you will see they are rather dark as opposed to the middle region of the iris. Also, add more variations in value in the iris; that might help with the crispness in the details there so it's not all smudged up together without definition. Well, hopefully these tips will help you more in the future :). Of course, you're already doing pretty well, so I'm sure you will get even better with time.