The Iriscope is a device capable of altering the user's irides.
When Leo Fitz joined Viro's crew onboard the Lazy Comet, he used the Iriscope to alter his irides so they would make him look like a Sivian so he would blend in. Continuing to pretend to be a Sivian, Fitz worked on the device and used it on himself protecting his identity. When the Sivian engineers became suspicious of Fitz, the followed him where they discovered he had been using the device. The Sivian Foreman punched him in the face, causing his irides to revert back to their natural state.