I did a 4-week sub-specialty rotation at a top program this summer, and I believe you have to define what you want to accomplish by doing a visiting elective. Most applicants in ophthal have 2 goals in mind: 1) Make a strong impression with the program and establish a personal connection 2) Get a good look at the program. I think the most helpful think to do if you are considering an away is to ask someone who did the elective as a student. In my case, I was made aware in advance that the attending expects med students to be *well versed* in the sub-specialty area and to start seeing patients independently pretty quickly; I planned the elective so that I'd have some time to read beforehand and get prepared. I think the preparation helped a lot; I think the attending was satisfied, I learned a lot, and had a great time! With that said, I've talked to a lot of residents who did aways and said that most people expect you to walk into an away with a basic fund of knowledge - just be enthusiastic, work hard, and be personable - and you'll be fine.
Bottom line: Find out what you're getting into. If you are really serious about a program it's a great opportunity to distinguish yourself from the many other great applicants out there. As one attending warned me, 'Don't forget that you will be compared daily with excellent students who are at home at their own institution and who know the low-down in advance. If you start out flat while you learn the ropes, the month may hurt you overall.'
