Kommentar zu Bereschit 27:1

ותכהין HIS EYES WERE DIM through the smoke raised by these women in offering incense to idols (Midrash Tanchuma, Toldot 8). Another explanation is: When Isaac was bound upon the altar and his father was about to slay him, at that very moment the heavens opened, the ministering angels saw it and wept, and their tears flowed and fell upon Isaac’s eyes which thus became dim (Genesis Rabbah 65:10). Another explanation is: They became dim just in order that Jacob might receive the blessings (Genesis Rabbah 65:8).

ותכהינה עיניו, due to old age, as we find in Samuel I 3,20 when the eyesight of the High Priest Eli failed due to old age.

ותכהינה עיניו, just as what happened to the High Priest Eli who had not protested the wrongs committed by his sons. (Samuel I 3,13) In that instance the expression used is ועיניו קמה ולא יכול לראות, (Samuel I 4,15) Neither Avraham nor Yaakov experienced such problems in their old age at the age at which Yitzchok was struck by this affliction. They were both far older than Eli who died at the age of only 98. In fact, the Torah reports Avraham’s youthfulness in 25,1 when it reports him as taking another wife. Yaakov, with all the troubles he had experienced during his life was still able to see at 147 years of age, though with difficulty, (may be was very shortsighted then) as in Genesis 48,8 he is reported as clearly seeing Joseph’s sons, though they may have resembled each other so that he could not tell apart which one was Efrayim and which one was Menashe, This was in spite of the Torah (48,10) having told us ועיני ישראל כבדו מזוקן, “Yaakov’s eyes were heavy with old age,” (problems keeping the lids open?) At any rate, he could see, though not with clarity.