Why Was Yitzchok's Vision Impaired?

(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 65:5). Another explanation is: They became dim just in order that Jacob might receive the blessings (Genesis Rabbah 65:8).

(1) ויהי אחרי מות אברהם ויברך וגו AND IT CAME TO PASS AFTER THE DEATH OF ABRAHAM THAT GOD BLESSED ISAAC etc. — Although the Holy One, blessed be He, had entrusted the blessings to Abraham to bless whomever he wished yet he (Abraham) feared to bless Isaac, because he foresaw that Esau would be born from him. He therefore said, “Let the Master of the blessings come himself and bless whomever it seems proper in his eyes” — God came and blessed him (Isaac) (Genesis Rabbah 61:6).