Odds of Hanging On
During your two-year training, you'll get extensive hands-on experience. Tons and tons of experience. If for some reason you decided you're not cut out for orthoptics, you can cut your losses and leave at any time. People who actually make it into this profession are pretty sure it's the right one for them. Couple that with the fact that the job market is only going to expand in the future, and we'd say your chances of hanging on are pretty good.
So long as you don't poke too many people in the eye.