The Gemara in Megillah states that it is forbidden to gaze at the face of an evil person. Chaza”l learn this out from the fact that Yitzchok lost his sight at the end of his life. The cause, according to Chaza”l, was Yitzchok’s gazing at Eisav’s face. Eisav’s great impurity caused Yitzchok to lose his vision.
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Rabbi Aharon Dovid Singer
Rosh Kollel, NMB Kollel
Director, South Florida Torah Initiative