The retina is really an outgrowth of the telencephalon. The most posterior layer of the retina is pigmented epithelium. The neural apparatus consists of three principal cell layers. At the back of the retina lie the photoreceptor cells called rods and cones. Rod discs contain the pigment rhodopsin.
Rods are responsible for colorless vision in dim light.
Cones function in bright light and are responsible for both sharp and color vision. Bipolar cells are those that rods and cones synapse with after receiving an image The third layer is made up of ganglion cells that receive input from bipolar neurons Directly posterior to the lens lies the macula lutea on the retina a small patch containing the fovea centralis that produces the most detailed image in vision. The iris contains two sets of muscles. The pupillary constrictor narrows the pupil to admit less light to the eye. The pupillary dilator widens the pupil to admit more light.