c. Internal Structures of the Eyeball.
(1) The nervous retina.
(a) The photoreceptors of the nervous portion of the retina (figure
11-11) contain chemicals known as visual pigments (rhodopsin). The cones are more
concentrated in the center at the back of the eyeball. The cones can register colors and
are used for acute vision. However, cones require more intense light than do rods. The
rods are distributed more toward the sides of the nervous retina. Although the rods are
capable of registering less intense light, rods perceive only black and white.
Figure 11-11. Cellular detail of the retina.