I was in a similar situation. I can only relay advice from my experience.
1. See if there is anyone famous in ophthalmology in your city/nearby. If you aren't close to a big program, the big-wigs may be more removed from academics now, but they may be happy to work with you. You can shadow them, do research, get to know them. I got 2 big-wig letters this way.
2. In my opinion, if you're going to go somewhere for just the purpose of getting a letter from one person, plan carefully. If that person is the program chairman/woman, it may be okay to do the regular rotation and let them know early that you are hoping for a letter. If that person is just on faculty...you may end up working with him/her for just one afternoon. So, if that's the case, I would recommend getting in touch with the doc and setting up an independent rotation. My other 2 LORs came from this strategy, and I think they had a lot more to say about me than someone who only worked with me for a day or so. Also, research rotations can bring you very close to attendings, and I loved the research rotation I did.
If you're going to do an away rotation, try to get a really solid understand about the structure of the away before you go. The aways can vary greatly.
Hope this helps
