20 Things You Didn't Know About Blade Runner
14. The "Replicant Eye Glint" Was A Technique Pioneered By Fritz Lang
Throughout Blade Runner, each replicant is shown with a red glint in their eyes at some point - seen prominently with the replicant owl in Tyrell's office, but first seen much more subtly in Leon's eyes when he takes the Voight-Kampff in the film's opening scene. Even Deckard's eyes appear to glow like this, hinting at his possible replicant identity.
This was not a contemporary visual effect however, but a technique known as The Shüfftan Process - created by Eugene Schüfftan, the cinematographer who was working for Fritz Lang on 1927's Metropolis, the original urban sci-fi dystopia. The effect was achieved by bouncing red light from a mirror angled 45 degrees from the camera onto the subjects' pupils - incredibly simple, but incredibly effective.