Can there be really so called perfect vision since 20/20 is considered normal vision?

Perfect vision: It is hard to come up with an exact answer of what perfect vision is. If we were to measure your eyes with a special wavefront scanner, and there were zero aberrations of any kind in the optics of your eye, than your vision would likely only be limited by the density of the photoreceptors and the nerves that communicate with them in the back of your eye at the retina. Probaly 20/8 vision.