Yoreh Deah Siman 267 Seif 33

 

לג הָיְתָה עֵינוֹ כֵּהָה קְצָת וְהִכָּהוּ בָּהּ וְסִמְּאָהּ, אִם מִתְּחִלָּה הָיָה יָכוֹל לְהִשְׁתַּמֵּשׁ בּוֹ קְצָת, יוֹצֵא בּוֹ לְחֵרוּת. אֲבָל אִם חִטְּטָהּ, אֲפִלּוּ לֹא הָיָה יָכוֹל לְהִשְׁתַּמֵּשׁ בּוֹ כְּלָל, יוֹצֵא לַחֵרוּת שֶׁהֲרֵי חִסְרוֹ אֵבֶר. וְהוּא הַדִּין בְּאֶחָד מֵרָאשֵׁי אֲבָרִים שֶׁהָיָה בָּטֵל וְאֵינוֹ עוֹשֶׂה בּוֹ מְלָאכָה, אִם חֲתָכוֹ יוֹצֵא בּוֹ לְחֵרוּת שֶׁהֲרֵי חִסְרוֹ אֵבֶר.

Seif 33

If his eye was not functioning well and then it was struck and he was blinded, if at the beginning he was able to use it (atleast) some, he goes free. However  if  the master cut it out, even if he wasn’t able to use it at all the slave goes free because the master caused him to lose an organ.

 

The same law applies with regard to any other of the tips of the organs that are not functional and cannot be used for labor, if they are cut the slave is released because of losing an organ/limb.