Write the function of each of the following parts of human eye:
Cornea: focuses light rays and permits the light to enter the eye.
Iris: Controls amount of light entering the eye and controls the size of pupil.
Crystalline Lens: Converges light rays onto retina.
Cilliary Muscles: Adjusts focal length of eye lens by contraction and relaxation so that sharp image can be obtained on the retina. It helps in accommodation.