Ha'azinu: Chapter 16
Opening the eyes

We learn that the eyes of Atika Kadisha never sleep, and for that reason have neither eyebrows nor eyelids. Both these eyes are actually one. The brain is called the fountain of blessing, and since it glows with the three kinds of whiteness in the eyes then blessings come out of the eye. Rabbi Shimon says that the Concealed Book taught him that the letters Yud Hei Vav Hei derive from Atika in order to support those letters below; for that reason the Holy Name is both hidden and revealed - the hidden part corresponding to Atika Kadisha and the revealed part to Zeir Anpin. Thus all blessings should contain both the hidden and the revealed.