If you're trying to advance your knowledge in preparation for [optometry school curriculum]: forget it and just wait until you start school. You don't need a leg-up on curriculum content, nor will any of this material make sense without perspective and context.
If you're trying to advance your knowledge about [optometry school or the field of optometry]: ASCO's
http://www.opted.org/
If you are a whiz kid who is bored and has plenty of time and money who just wants to read stuff akin to reading wikipedia, you can also shell out several hundred dollars for Rosenfield's textbook (
https://books.google.com/books/about/Optometry.html?id=dv2g8aOIhhsC), which I thought was a perfect read for the intro student that encompasses most of what one would learn in years 1 to 3. This book was my favorite text from my school's library when i read it my 2nd year of optom school.
But again I'd not worry about this and recede back to where you came from, so help you...