THE EYE OF HORUS

In the hieroglyphs of Ancient Egypt we find mention about the Eye of Horus, also known as the Udjat, wadjet, or Oudjat, which is a symbol for spiritual awakening, protection, the power of royalty and good health. Horus is a god from Egyptian mythology, who defeated powers of darkness, established order, harmony and productivity. Horus was the offspring of Isis and Osiris. 
When Osiris became the king of Egypt he was a good and just king; he established the rule of the law (Maat), and with the help of the god Thoth, he taught a new religion to men and the arts of civilization, thus, Egypt became prosperous and had peace.
However, his brother Seth feeling jealous, plotted against him, and Osiris was murdered. Then Isis, his consort, with the help of Thoth, brought Osiris back to life, and soon after, Horus was born. 
Osiris' task on earth was then completed, and he transfigured himself into a star being, which is Orion constellation, and went to be a ruler of the Kingdom of the dead, the Duat. 
Isis by her turn, is identified with Sothis (Sirius), being the astral mother of the living king. Sirius, the brightest star in the sky and its constellation, Canis Major, immediately follows Orion in its rising.
Horus grew up to be a prince, and later revenged his father Osiris, and when fighting Seth, Horus lost his left eye. The god Thoth then helped Horus, restored his eye, which then became a symbol of protection for the living and the dead, and he was proclaimed the king of Egypt.

There is a theory that the eye of Horus could be a map of the brain.

When we compare the symbol of Udjat (eye of Horus) with the picture of the brain, we can see a similarity. 

The eye represents the thalamus, the eye brow is the corpus callosum, the tear duct and tear drop symbolize the pituitary and medulla oblongata. The long spiral arch that goes down the eye is the cerebellum, and the small point on the end is the pineal gland, or third eye.

The Egyptians had many amulets depicting the Udjat which accompanied them to the afterlife, which were decorated with semi-precious stones on bracelets, necklaces, and pendants.. It was intended to protect the soul from harm and bad luck during the journey.