Well that's... odd. Perhaps they just assume that since they mentioned an Astropath was blind, one would play them as such and apply negatives and prohibit actions based on common sense?
When talking about psyniscience as a sensory power, again, as this is a stand alone game, that should have been included... perhaps in the description of psyniscience? Either way, going by IH, they can use psyniscience in place of awareness when detecting life forms so, it would act as a crude form of sight (well awareness of where folks are and kinda what they might be doing but watch out for that wall!).
In the original Rogue Trader, Astropaths were described as having a "near sense" , an enhanced spacial awareness that came from being soul bound which allows them to sense normally visible things within 20m of them. I know a lot of the original Rogue Trader doesn't apply to 40k any longer but perhaps they still are able to do this. If so, then it should have been discussed or described somewhere. I don't have the book yet so I can't rummage through it to find any mentioning of such in odd non-intuitive places.
So, off of what i know and not having the book yet, I would treat Astropaths as being blind unless they make a psyniscience test which would allow them to get a very general lay of the land when it's important but with no visual details (colors, detailed features, distinguishing marks, etc). I would also give them a -20 to tests that require sight as if they had One Eye as opposed to being completely blind.
which makes me wonder, do they get the trait Blind Fighting at any point during their career? It seems right up their ally...