Second cranial nerve: The second cranial nerve is the optic nerve, the nerve that connects the eye to the brain and carries the impulses formed by the retina -- the nerve layer that lines the back of the eye, senses light and creates the impulses -- to the brain which interprets them as images.
The word "optic" comes from the Greek "optikos", pertaining to sight.
The cornea is the clear front window of the eye that transmits and focuses light into the eye.
The iris is the colored part of the eye that helps regulate the amount of light that enters the eye.
The pupil is the dark aperture in the iris that determines how much light is let into the eye.
The lens is the transparent structure inside the eye that focuses light rays onto the retina.
The retina is, as mentioned, the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain.
The macula is a small area in the retina that contains special light-sensitive cells and allows us to see fine details clearly.
In sum, the optic nerve is uniquely a part of both the eye and the brain. It is embryologically the brain's envoy to the eye and functionally the eye's envoy to the brain.