The human eye has a biological control system that varies the pupil diameter to maintain constant light intensity to the retina. as the light intensity increases, the optical nerve sends a signal to the brain, which commands internal eye muscles to decrease the pupil's eye diameter. when the light intensity decreases, the pupil diameter increases. draw a functional block diagram of the light-pupil system indicating the input, output, and intermediate signals; the sensor; the controller; and the actuator.