Genesis: 27:1 – It came to pass when Isaac was old, and his eyes were too dim to see, that he called Esau his elder son, and he said to him, “My son,” and he said to him, “Here I am.”
Babylonian Talmud – Megila 28a: Rabbi Eleazar said, “ Anyone who stares at the face of an evil person will cause his eyes to be damaged. This is shown by the verse: It came to pass when Isaac was old and his eyes were too dim to see”. This was due to Isaac’s staring at Esav, the evil one.
Torah Temimah Colloquial Translation on Note #2
See above in Parshat Vayera (Genesis 20:16) that Abimelech cursed Sarah that she should have children with weak eyes. This curse was fulfilled through Isaac. The Gemora asks was it through looking at Esav or due to the curse of Abimelech. The Gemora responds that both reasons contributed.
Prior to this discussion, the Gemora discusses the point that one is forbidden to stare at the face of an evil person. It must be that the phrase “forbidden” is not precise; rather, it is not a good personality trait to stare at the face of an evil person. The proof that it is not literally “forbidden” is from the story that the Gemora tells relating to this issue. The story is that Rabbi Yehoshua ben Karcha is asked “In what merit have you earned to live a long life?” Rabbi Yehoshua replied that he had never stared at the face of an evil person. Note that if it were literally forbidden, what would be special about not having committed that particular sin?
Also, do not be concerned about the phrase “forbidden” that is used in the Gemora. We find many examples of similar exaggeration. For example, the Rosh writes at the end of the first chapter of Avodah Zarah that it is forbidden to have a [business] partnership with a non-Jew. Behold, this is not at all forbidden, not even rabbinically. Rather the Rosh meant that it is praise worthy trait. Also see Tosafot’s comments in Gemora Bechorot 2b.
As a general observation, also note that the word “stare” refers specifically to depth and emotional looking not to superficial “seeing”. The proof for this is that we have a well know law that one who sees a rainbow should make a blessing upon seeing it. How would this law be possible given that we also state in the Gemora (Chagiga 16a) that anyone who stares at a rainbow will damage his eyes. One must conclude that “staring” and “seeing” are two different levels of looking at something.
We see the same point from the Gemora there regarding the saying that anyone who stares at the face of a prince, will cause his eyes to be weakened. On the other hand, the law is that when a prince passes by, one should stand up and look at his face with awe (Horayot 12a).
Translator’s Note: This note stood out to me because the Torah Temimah states that sometimes when the Gemora or later rabbinic texts state “forbidden”, it is not literally forbidden.