Eyes of Kurnous
The Eyes of Kurnous are shards of brilliant crystal, which according to the Eldar's legends, are fragments of the perfect eyes of Kurnous, the Legendary Hunter and God. Kurnous was revered for keen sight - both across the fields he hunted and into the hearts of the people.
When Slaanesh attacked the gods of the Eldar, it was Kurnous who first saw the approach of the Chaos power. But Kurnous was imprisoned then, bound by the jealous god Khaine within chains of fire. Thus, Kurnous was unable to call out his warning cry. When Slaanesh discovered him, it grew resentful of his perfect sight. A vain and narcissistic creature, it could not stand to be seen by him in all its hideous corruption. And so it turned his eyes to crystal, then tore them from his head and shattered them, flinging the shards across all the worlds of creation.
Over the ages, Eldar have discovered these crystals on myriads of worlds. The shards, an eternal reminder of the Eldar legacy, grant sight beyond sight and vision beyond vision to those who bear them. Even allowing them to see enemies invisible to mortal eyes.