The eye is the sense organ where the first
stage
of the complex and manifold process of vision takes place. The eye is in charge of focusing and registering light, creating a
clear
and sharp
image
and transforming the light into neurological impulses. Seeing is possible when enough light reaches the eye. This requires both a large enough object reflecting the light and a strong enough intensity of light.
The light which reaches the eye is regulated by the pupil, acting like a camera shutter, so that the amount of light which the eye actually uses is often a mere fraction of the light which reaches the eye. Other parts of the eye then become involved in the process of seeing: the cornea, aqueous humor and the lens, causing an
image
of the viewed object to be projected onto the retina. A person with normal eyesight, at a proper
level
of light, can discern minute details: a telephone wire 500 meters away, or a 0.3 mm thick thread at a distance of 20 meters. Yet this amazing sensitivity is repressed when there are rapid changes in the brightness of the light.
