Bava Kamma 84: An Eye for an Eye

When the Torah says, "an eye for an eye," how is that the Gemara concludes that the perpetrator compensates for the damage with money, rather than coming after him physically? Also, the deep topic of how to assess damages - to compare the injured party to a slave, which was, perhaps, logical, but nonetheless off-putting. Also, this particular assessment was only done in Israel, and not to be used in Babylonia.