The Eye of Horus was believed to have healing and protective power, and it was used as a protective amulet. It was also used as a notation of measurement, particularly for measuring the ingredients in medicines and pigments. The symbol was divided into six parts, representing the shattering of Horus´ eye into six pieces. Each piece was associated with one of the six senses and a specific fraction.
Horus was an ancient a sky god whose eyes were said to be the sun and the moon. However, he soon became strongly associated with the sun while Thoth was associated with the moon. An ancient myth describes a battle between Horus and Set in which Horus´ right eye was torn out and Set lost his testicles! Thoth magically restored Horus´ eye, at which point it was given the name "Wadjet" ("whole" or "healthy"). In this myth it is specifically stated that it is Horus´ left eye which has been torn out, so the myth relates to the waxing and waning of the moon during which the moon appears to have been torn out of the sky before being restored once every lunar month.
There are a number of depictions of the restoration of the eye in Greco-Roman temples. Thoth is assisted by fourteen gods including the gods of the Ennead of Hermopolis or thirty male deities (in Ismant el-Kharab, the Dakhla Oasis). Each god represented one of the fifteen days leading up to the full moon, and to the waning moon. The restored eye became emblematic of the re-establishment of order from chaos, thus closely associating it with the idea of Ma´at. In one myth Horus made a gift of the eye to Osiris to help him rule the netherworld. Osiris ate the eye and was restored to life. As a result, it became a symbol of life and resurrection. Offerings are sometimes called "the Eye of Horus" because it was thought that the goods offered became divine when presented to a god.
According to later traditions, the right eye represented the sun and so is called the "Eye of Ra" while the left represented the moon and was known as the "eye of Horus". However, in many cases it is not clear whether it is the left or right eye which is referred to. Others myths suggest that it is Horus' right eye which was torn out and that the myth refers to a solar eclipse in which the sun is momentarily blotted from the sky.