Freedom was the proper equivalent for permanent injury.
Related Commentaries of Exodus 21:26
Exodus 21:26-27
26 And if a man smite the eye of his servant, or the eye of his maid, that it perish; he shall let him go free for his eye's sake.
27 And if he smite out his manservant's tooth, or his maidservant's tooth; he shall let him go free for his tooth's sake.