Eyeless

The Eyeless were an alien species from an unknown planet. They appeared to be made out of glass and when when killed, shattered. They needed to take human eyes to be able to see. One of the Eyeless stole some green eyes from a young girl. The Eyeless arrived at the Fortress to use the weapon at its heart. However the Fortress turned out to be alive and it fought off the Eyeless killing hundreds of them. In the end the Eyeless activated the weapon but it was a dud like it was the first time. (NSA: The Eyeless)