Historically, most people have favoured their right hand, with the result that the right side was generally seen as more powerful/significant than the left. 1 Thus, people would rather lose their left eye and their left hand than their right. By mentioning the right hand, Jesus is saying that your most important and significant appendage is not nearly as important as making sure that you are not thrown into the fires of hell.
29 Si ton œil droit est pour toi une occasion de chute, arrache-le et jette-le loin de toi; car il est avantageux pour toi qu'un seul de tes membres périsse, et que ton corps entier ne soit pas jeté dans la géhenne.