Reference for Kiddushin 48:17

ואידך מושחת שחתה נפקא ואידך שחת שחתה לא דריש

Now, both are necessary. For if we were taught the first [only], [I would say] that is because his eyesight was originally sound and now it is weak; but here [in the second Baraitha], seeing that his eyesight was impaired before too, I would say [that he does] not [go free]. And if we were taught the second: that is because he completely blinds him; but there [in the first Baraitha] that he does not completely blind him, l would say [that he does] not [go free].

Jastrow