The only differences I can recall are:
- Optoms get a choice between a biology course or psychology course (most students will choose the psych), while vision science students do a course called SCIF. SCIF is one of the easiest courses you will ever come across, and it's a good opportunity to meet people too outside of optometry. It's mostly just building teamwork and having a lot of group projects.
- You'll do your courses in a different order, depending on how the uni organises it for your year. Eg. vision science students did physics in second semester instead of first. It's actually a bonus because you can get all the quiz answers from your friends (it's always the same), and even some online assessments never change =)
If there's anything else it would be minor since I can't remember it. First year of optom/vision science is mostly hsc science, and an introduction to basic anatomy of the eye (you'll definitely need to listen and get a good grasp of the anatomy course though since it's your foundation for everything). There's no major disadvantages by doing vision science, and in my opinion, since I was a vision science student too, it's probably easier since SCIF is such a WAM booster. The real optometry learning doesn't start until 2nd year.
HNY and good luck!
Oh, and as a side note, if you didn't know: as a vision science student you'll be in most of the same classes as optoms anyway. And when you transfer, you transfer straight into 2nd year, so you're not behind at all.