What does the Torah mean when it writes "Ayin Tachas Ayin"?
Rashi, Ramban (Refer to 24:18:1:1*) and Targum Yonasan: It cannot mean literally 'an eye for an eye'. 1 What it therefore means is that he must pay the victim's value 2 - as if he was being sold as an Eved. 3
Because, as the Gemara explains in Bava Kama 83b, 84a, 'What if the eye of the striker is larger than the eye of the victim?' (the first of a number of reasons given there).
Rashi: Which explains why the Torah writes an expression of Nesinah ("Kein Yinasen bo") - 'something that is handed over from one person to another'.