To what extent can bacteria actually see?
Simple answer is that many simple organisms, including bacteria, carry light-sensitive molecules. One example is halorhodopsin (not bacterial but archaeic). This is a molecule, light-gated ion pump, that reacts to light, thus allowing organism to react to photons by changing concentration of certain ions inside the cell.

Study from Stanford described similar molecule found in bacteria.

In conclusion, if by "vision" you understand ability to react to light in the visible part of the spectrum, then a lot of organisms possess such ability. However, they lack other crutial parts of human vision.