Kabbalah su Genesi 48:10

Rabbi Elazar, his son, kissed his hands and said, This is well. Abraham shines on the side of his grade, and Isaac is darkened on the side of his grade. But why did Jacob (grow darker), as it is written, "Now the eyes of Yisrael were dim (lit. 'heavy') from age" (Beresheet 48:10). He answers, Assuredly it is, for it is written, "heavy," and not dim; It is written "from age", not 'his age.' "From age" is to be interpreted as the age of Isaac, on the side (of Isaac) his eyes "were heavy so that he could not see" (Ibid.), not properly, but he was not absolutely blind. But Yitzchak's eyes were completely dim, and it became darkness, for night clove to him and it was fulfilled, "and the darkness he called Night."