About the human eye
The human eye, the organ responsible for the sense of sight, is a very complex structure. We use our vision in almost every activity, so the eye is a most important organ.
How vision works
Sight begins when light rays from an object enter the eye through the cornea, the clear front “window” of the eyeball. The cornea is actually responsible for about sixty percent of the eyeball’s light-ray-bending capability. The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil, the size-changing hole in the iris.
The iris, the structure that gives the eyes color, works like a shutter in a camera. It has the ability to enlarge and shrink, depending on how much light the environment is sending into the pupil.
After passing through the iris, the light rays strike the eye’s crystalline lens. This clear, flexible structure works much like the lens in a camera – shortening and lengthening its width in order to focus light rays properly.
In a normal eyeball, after exiting the back of the lens, the light rays pass through the vitreous — a clear, jelly-like substance that fills the globe of the eyeball. The vitreous humor helps the eye hold its spherical shape. Finally, the light rays land and come to a sharp focusing point on the retina.
Continuing with our “camera” analogy, the retina’s function is much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses through over a million nerve fibers to the optic nerve.
The optic nerve is sort of like an extension of the brain. It is a bundled cord of more than a million nerve fibers. The light impulses travel through this nerve fiber to the brain, where they are interpreted as an image.