The Eye is capable of scanning great distances in hyperspace. In early 2260, when Susan Ivanova was linked to the Great Machine, she was able to send her mind out throughout the cosmos looking for the First Ones. During her "journey," she encountered the Great Eye, but luckily was able to flee from it.
Once at Z'ha'dum, the rescue party scans the planet while Lyta probes telepathically. The Shadows soon become aware of them, and the Great Eye speaks to Lyta Alexander, Susan Ivanova and Delenn, beckoning them to bring the ship down to the planet. Each heard it speak in the voice of their father. Luckily, Lennier pulls them away and back into hyperspace.