Light enters to the eye through cornea, subsequently traveling to the Aqueous humour, pupil, lens and Vitreous humour before reaching the retina,Cornea is transparent layer of fibrous connective tissues that has no blood supply, Cornea is first intera-ocular structure that refract or bends the light rays.
After passing through cornea light passes to the aqueous humour. Aqueous humour is a clear fluid continually produced by capillaries in the ciliary body, Function of Aqueous humour is to maintain the shape of the front of the eye and to supply oxygen and nutrients to both cornea and lens.
Next Light travels through pupil, the circular opening located in the center of iris.Iris is the color portion of eye, which contains two sets of smooth muscle fibers that contract to control the diameter of the pupil.
In order to transmit relatively constant level of light to the retina, the size of the pupil regulates amount light entering eye by either constricting or dilating.In bright light or situations that require near vision, pupil constricts to reduce the amount of light passing through lens; this reaction is known as pupilary light response or accommodation papillary reflex.
Pupil also helps to bring objects into focus by adjusting the depth of focus