The Eye of Horus is a symbol of protection, royal power and fertility. Original painting: acrylic on canvas. By Barbie Hardrock, 2008. (www.barbiehardrock.com)
In one version of the story, Horus gets into an argument with his brother Seth, both fighting for their fathers throne.
Seth cuts out one of Horus´eyes (in another version even both) and this eye, healed by Thot later on, is represented as the „Moon Eye“. With this moon eye, Horus could make his father Osiris come alive, and this is why this symbol ment healing and vitalization to the old Egyptians.
(Source of information: Wikipedia, egyptian mythology)