Sometimes the eye is very visually distinct. Bizarre irises or unusual pupils mark the individual. Working on the principle of the eyes being the window to the soul, these Technicolor Eyes can be a small but direct method of demonstrating the fact that an otherwise normal-looking individual is at least partially cybernetic. In the case of prosthetic eyes they also work as a scar signifier. Since the eyes are taken as so much more personal they can be a much smaller effect for greater emotional impact. And, of course, it can also show how evil a person is. here