How the Eye Works
The basic function of the eye is often compared to a simple camera.
Light travels in straight lines but bends when it hits another transparent medium.
The cornea is the curved front surface of the eye. When a ray of light hits this curved surface, it bends. It is here that most of the refraction occurs. The refractive index is approximately 1.376, which is comparable to that of glass or plastic.
The iris is the coloured part of the eye. It adjusts automatically to control the amount of light entering the eye.
The pupil is the hole in the iris through which the light enters. It enlarges when there is less light, so as to allow the maximum possible light to enter. It becomes smaller when you are in the presence of bright light.
The lens is the transparent structure inside the eye that focuses light rays onto the retina. It is flexible and changes its shape and focal length. When we look at faraway things, the lens is pulled flat by little muscles. When we look at close-up things, the muscles pull in and the lens gets fat and round. This way, the eye is able to look at things near as well as far.
The retina is the nerve layer that lines the back of the eye. When your eye focuses on an object, all the light rays from a single point on that object are bent toward a single point on your retina. The odd thing is that the images are inverted as they impinge on the retina! (This is because the rays of light are bent by a double convex lens!) The retina senses light and creates impulses that are sent through the optic nerve to the brain.
The macula is a small area in the retina that contains special light-sensitive cells. The macula allows us to see fine details clearly.
The optic nerve is the nerve that connects the eye to the brain. The optic nerve carries the impulses formed by the retina to the brain, which interprets them as images.
By the time this happens, you have not just seen, you have perceived. Vision is not so simple as we have made it sound. Two people look at the same scene and see different things. We recognise things with different associations. In these ways seeing is so closely connected to the understanding of what is seen – perception.