וַיְהִי֙ כִּֽי־זָקֵ֣ן יִצְחָ֔ק וַתִּכְהֶ֥יןָ עֵינָ֖יו מֵרְאֹ֑ת וַיִּקְרָ֞א אֶת־עֵשָׂ֣ו ׀ בְּנ֣וֹ הַגָּדֹ֗ל וַיֹּ֤אמֶר אֵלָיו֙ בְּנִ֔י וַיֹּ֥אמֶר אֵלָ֖יו הִנֵּֽנִי׃
At nangyari, nang matanda na si Isaac at lumabo na ang kanyang mga mata kaya hindi na siya makakita, tinawag niya si Esau, ang kanyang nakatatandang anak, at sinabi sa kanya: “Anak ko.” At sinabi nito sa kanya: “Narito ako.”
Rashi
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).
Alshekh
He called Eisov. He intended to bless Eisov with the bounties of this world and Yaakov with those of the next. But Rivkah was afraid that if Eisov ruled the world and Yaakov fell into his hands, he would not survive. Therefore she wanted Eisov’s rule to be limited and Yaakov to inherit this world as well.
Chizkuni
ותכהינן עיניו, his eyes had become weak; but not Rivkah’s eyes; this is so because woman was created from man’s bone, as were the wives of Esau, and we have a rule that one bone does not harm another bone. {Tanchuma Toldot 8)[When bone hits bone nothing breaks. When bone hits vessels made of earth(enware) the latter is liable to be shattered. When G-d made Adam, He used earth. Ed.] An alternate exegesis: Rivkah’s eyes, which had been used to the smoke emanating from sacrifices offered to idols, had become immune to that smoke from childhood.