The primary function of the visual system is to assist in interactions with our environment by recognizing the nature of the objects
 around us and enabling us to move through and act on that
 environment.

Our visual system creates a mental model of our world to enable this, one that is very different from the retinal image from which it originates. To understand how your visual experience is changing, it is helpful to understand how your mental model of the world can be affected by disease and changes to the visual system.