That’s not quite true; you have far more neurons going to the retina than you have coming from it. The retina supplies a surprisingly small amount of bits per second to the brain. Neuroscientists believe that at least half of our conscious experience of reality is effectively “hallucinated” by the brain based on internal models it has built from past experiences. So it’s highly plausible that that same perception-generating system which creates your conscious perception of reality could also function while asleep.