The retina is made up of rods and cones . Rods are highly sensitive to light and allow us to see under low levels of illumination. However, they are unable to resolve fine detail and are subject to saturation. This is the reason for the temporary blindness that is caused when we move from a dark room into sunlight. There are approximately 120 million rods per eye which are mainly situated towards the edges of the retina.
Cones are less sensitive to light than rods and can tolerate more light.
There are three types of cones, each of which is sensitive to a different wavelength of light. These cones which number about 6 million are mainly concentrated on the fovea , a small area of the retina on which images are formed. The information that is that is gathered by the eye must be filtered and passed to the brain, which in turn generates coherent images. We shall look at different aspects of the perceptual process. Reflected light from an object forms an inverted image on the retina of the eye.