Light slows down when it enters glass.
Imagine having one piece of glass with an amazingly high refractive index over one eye and nothing over the other. The light passing through the glass would be slowed down and arrive at the eye later than the light that hasn't gone through the glass. So one eye would be seeing in 'real' time while the other was seeing stuff with a delay on it. This is a stand-alone question which will eventually become integrated into the linked database.