Eyes of the Serpent
Two of these exist on the Serpent Isle: the blue eye of Order and the red eye of Chaos.
Their function is simple: together they can call the Great Earth Serpent in the Shrine of Balance, when put on the altar in front of the Wall of Lights. The fate of these two items is quite different.
The Eye of Chaos
The Eye of Chaos was brought to the Isle of Crypts by the forces of Order. There, the Avatar needed the Blackrock Serpent of Balance to pass and find the Eye behind a force field. Dispelling the field, the Avatar took the Eye and later used it in the Shrine of Balance to call the Great Earth Serpent.
The Eye of Order
The Eye of Order was stored in the Shrine of Balance, and the Avatar had to put three of the Serpent Artifacts (Staff, Crown, Armour) on the right altar to receive it. A short while later the eye was used to call the Great Earth Serpent.