In one panel we see roshi with his glasses on and he would have realized if it was gone before the rays hit his eyes IF goku took them before tiens attack. Tien solar flare the ring, goku makes it to roshi in enough time to get the glasses AND put them on AND run back to the spot that he was at before the solar flare completely engulfs the field. Roshi without his glasses gets blind, then he realize that his glasses were gone.
If goku took them before the blast, roshi would have known a lot sooner than what he did since they are "shades". You all tend to forget that roshi have super speed as well so someone taking something from him without him noticing it is a feat within itself.
Goku outran the blast by a large pace and did a couple of things before the blast even registered.