Visual system: Encyclopedia II - Visual system - Eye

Visual system - Eye

The eye is a complex biological device. The functioning of a CCD camera makes an apt metaphor for the workings of the eye, which takes visible light and converts it into a stream of information that can be transmitted via nerves.

Light entering the eye is refracted as it passes through the cornea. It then passes through the pupil (controlled by the iris) and is further refracted by the lens. The lens inverts the light and projects an image onto the retina.

The retina consists of a large number of photoreceptor cells which contain a particular protein molecule: the photopigment called rhodopsin. When rhodopsin is struck by a photon (a particle of light) it transmits a signal to the cell; the more photons strike the cell, the stronger the signal will be. In some animals, like humans, cone cells contain cone opsin molecules attuned to specific wavelengths of light; i.e., a blue cone cell contains opsin most attuned to blue-wavelength light and will most strongly be stimulated by blue-wavelength light, while a yellow-red cone cell will only be weakly stimulated by blue-wavelength light. This gives the ability to distinguish color.

Adapted from the Wikipedia article "Eye", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki