מדרש אויף 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.

[3] Another interpretation: when Isaac grew old, it is written above that "Esau was forty years old, and he took as wives Judith the daughter of Beeri the Hittite, and Basemath the daughter of Elon the Hittite, and they made life bitter for Isaac and Rebekah." (Genesis 26:34-35). "A foolish son is a vexation to his father, and bitterness to her that bore him." (Proverbs 17:25). Yet, despite all of this, his father called him "the elder." "And Isaac called Esau his elder son" (Genesis 27:1), and his mother called him "the elder," as it says, "And Rebekah took the goodly garments of her elder son Esau" (Genesis 27:15). The Holy One, blessed be He, said, "Behold, there are the old and the aged who lack understanding, but I called him 'small,' as it is said, 'Behold, I have made you small among the nations'" (Obadiah 1:2). This is similar to a person who had a text to write that said, "heroic knights." Someone came to him to have his son's name inscribed and said to him, "Look at my son. He is young, but tall and sturdy." His mother also said, "Look at our son. He is tall and sturdy." He replied to them, "He is tall and sturdy before you, but I do not know. After all, the scale (i.e., measuring tool) will determine his true height. If he is indeed tall, then he will be measured and found to be tall. However, if he is not tall, then he will be measured and found to be small and disqualified." Thus, Rebekah called him "the elder," and Isaac called him "the elder." The Holy One, blessed be He, said to them, "Who else in My world is sovereign and rules without Me? As it is said, 'Who is he that speaks, and it comes to pass, unless the Lord commands it?' (Lamentations 3:37). He said to them, "Why do you insist on calling him 'the elder' in My house? I made him small." And you call him 'the elder,' but he is only small, as it is said, 'Behold, I have made you small among the nations'" (Obadiah 1:2).

“Esau was forty years old, and he took as a wife Yehudit, daughter of Be'eri the Hitite, and Basmat, daughter of Elon the Hitite” (Genesis 26:34).
“Esau was forty years old” – that is what is written: “The swine from the forest gnaws at it” (Psalms 80:14). Rabbi Pinḥas in the name of Rabbi Simon: Of all the prophets, only two of them publicized it¹The qualities of the evil empire of Rome. – Moses and Asaf. Moses said: “The pig because it has a split hoof” (Deuteronomy 14:8). Asaf said: “The swine from the forest gnaws at it.” Why does he analogize it to a pig? Just as this pig, when it lies, it extends its hooves, saying: ‘I am pure,’ so, this evil empire robs and takes forcibly, [yet] it appears as though it is arranging the courtroom. So, Esau, all forty years, would ensnare married women and violate them. When he reached forty years of age, he likened himself to his father. He said: ‘Just as Father took a wife at forty years of age, I, too, will take a wife at forty years of age.’ That is what is written: “Esau was forty years old.”