Starting with light and ending in sight
Vision begins with the cornea, at the front of the eye, since it refracts incoming light into the pupil, the dark opening in the eye. The iris, the colored ring surrounding the pupil, opens and closes to control the amount of light entering through the pupil. Once past the pupil, the light passes through the lens, which further refracts the light onto the back of the eye.
Transferring visual information to the brain
A thin layer of tissue called the retina covers the back of the eye. The retina is made of millions of receptors and nerves that detect the image formed by the optics of the eye much like the pixels of a digital camera. These nerves send information to the optic nerve, which transfers information to the brain. If both eyes function properly, information from both eyes is merged together into a single, three-dimensional image by the brain, allowing us to see the world with a sense of depth.
Perfectly focused vision
The condition resulting in normal, perfectly focused vision is called emmetropia, derived from a Greek word meaning equally measured. The proportions of the eye have to be exact so that light is brought into sharp focus at the back of the eye. Where the focal point lands, in reference to the lens, determines the eye’s refractive power. Your refractive power is measured in diopter, which is 0 dpt for emmetropia.