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Eye physiology is the study of the physiological processes involving the eye and all related structures. This science draws upon chemistry, physics, and anatomy. It describes the mechanism the human body uses to interpret light in ways that aid in the understanding of the world.
The eye and all processes associated with it are complex, so the term eye physiology is a rather broad one to say the least. Physiology, in layman's terms, may be thought of as how stuff works. If anatomy is what stuff is made of, physiology is what these things actually do. For example, eye anatomy may describe the pupil, cornea, or other structures, whereas eye physiology would articulate how rays of light are transformed into sight.
Sight is a necessary function in many things that animals do, and although not necessary for life itself, it plays an important role in experiencing the world. Viewing a mountain range, avoiding a thrown object, experiencing physical attraction — each of these common activities would not be possible without the proper physiological function of the eye. Simply put, light is made up of small particles that bounce off of objects and into the eyes. It is then picked up by sensory cells and transformed into electrochemical impulses later interpreted by the brain.
The best way to have a functional perception of eye physiology is to liken it to that of a more tangible, familiar object: a camera. The cornea, or outside of the eye, may be thought of as a camera lens, and it is responsible for about 60% of light focusing. The partially focused light's next stop is through the pupil and iris, where their aperture-like qualities control the volume of light allowed to pass through. In dark areas, this volume is rather high, whereas bright rooms may cause the opening to decrease, resulting in the change of pupil size.
This more finely focused light eventually reaches a structure at the back of the eye known as the retina, where light-specific rods and cones act to translate their reception of light into an impulse that travels to the back of the brain. Cones pick up on colored light, whereas rods are more or less light and dark receptors. The level of their excitability by light changes the impulses they send, thereby affecting the image that is actually seen or interpreted by the brain.