How to find and delete duplicates in albums

Good Morning, I just created an album in iPhoto 11 with 400 photos and manually sorted in preparation of making a saved slideshow. Is there an easy way to find and delete any duplicates in this album with changing the sorting order? I know that I could go back and sort by name and easily find them, but if I do that could I revert back to my manal sort minus the duplicates? Thanks in advance - Deborah