Vision starts in the eye (big surprise). Light enters through the pupil (the black part of your eye) and travels through the lens, which helps to focus, especially to objects that are close to us, and then to the back of the eye, called the retina. In order to reach the retina, the light must travel through several layers of cells in the retina - first through ganglion cells, then bipolar cells and then to photorecepters. The photorecepters are the light sensitive cells in the retina. Light is absorbed by photopigments in the photoreceptors. Absorption sets off a series of events in the photreceptors which lead them to hyperpolarize in the presence of light. This information is then passed to the bipolar cells and then to the ganglion cells. The axons of the ganglion cells form the optic nerve that leads to the brain.
The optic nerve from each eye travels back until the two nerves meet in the optic chiasm, then they split again to form the optic tracts. In the optic chiasm a partial decussation of the optic nerves occur. In normal language it essentially means that some of the information from the right eye crosses over to the left optic tract and some of the information does not cross over but goes straight back to the right optic tract. The same thing happens to the left eye. This partial decussation allows both sides of the brain to recieve information from both eyes. (If you haven't noticed yet you don't see the same exact thing with both eyes. If you did the crossing over that occurs in the optic chiasm would be pointless.) Most of the axons in the optic tract innervate a structure called the lateral geniculate nucleus of the dorsal thalamus or LGN for short. The right optic tract innervates the right LGN and the left optic tract innervates the left LGN.
The LGN has six layers which recieve information from different kinds of ganglion cells from the retina. From the LGN information is relayed to the primary visual cortex located on the occipital lobe of the brain. The primary visual cortex has nine layers, each layer has distinctive features and recieves input from other layers and the LGN. Communication between different layers, blob cells and ocular dominance columns, the M channel, P-IB channel and orientation columns can get pretty complicated and since this is a sort of crash course in vision I won't go into any more detail about what layer has what and where they get there information from. However I will leave you with a some things to ponder.
With all the information that our eyes are constantly bombarded with how do we sort and label what we see? Each of the receptors in our retina take in a little piece of information which is quickly processed to form what we see. How does this occur so rapidly? Our vision is constant - that is we don't see things as a jumble of lines that come into focus every once in a while - objects are always there and don't disappear and reappear when our brain has the time to process information. Besides processing what we see, the areas of our brain that deal with vision must also have connections with many other parts of the brain such as areas that deal with motor skills and memory. This is what allows us to quickly react and catch a falling object or find our way back by using landmarks when we get lost in an unfamiliar place. Somehow the brain is able to process all the information we need into a usable form without us even having to think about it. Think of that the next time you catch a falling glass or jump out of the way of a fast moving car and you too will be amazed at your brain.