מדרש על בראשית 26:34

And his eyes were dim (Gen. 27:1). And when Esau was forty years old, he took to wife Judith the daughter of Be’eri the Hittite, and Basemath the daughter of Elon the Hittite. And they were a bitterness of spirit unto Isaac and to Rebecca (Gen. 26:34–35), and this is followed by the verse And his eyes were dim. Hence, they must have become dim because of his unhappiness.