Hole which allows light to pass through. Size controlled by muscle of iris. Retina - sensory portion of the eye. Rhodopsin and Iodopsin - light sensitive pigments. Light entering the eye first passes through the cornea, which bends light to focus on the retina.
Ciliary muscle attached to the lens shapes the lens to complete the focusing of light on the retina.
The iris regulates the amount of light entering the eye so that light sensitive rods and cones are not overwhelmed and begin to fire continuously.