The Udjat Eye is an accessory item found locked inside the Big Chest, which is opened with a Key.
The chest containing the eye is guaranteed to appear somewhere on the 2nd, 3rd or 4th level of the Mines.
It is the first of four special Ancient Egyptian artifacts required to reach the City of Gold.
Additionally, it makes loose treasure lying on the ground easier to see by superimposing it over the terrain so that it does not get obscured by rocks or grass.
It does not reveal items that spawn inside walls however, so does not make the spectacles completely redundant when acquired.
As you approach the location of the entrance, the Eye will start blinking in your inventory and making a squeaking sound, which increases in frequency the closer you draw to the hidden door.
The "Eye of Udjat" is another term for the Eye of Horus, an ancient Egyptian symbol representing the protection of the gods.