The front part of the eye is covered by a transparent spherical membrane called the cornea.
Light enters the eye through cornea. The space behind the cornea is filled with a liquid called aqueous humour.
Just behind the cornea is a dark coloured muscular diaphragm called iris which has a small circular opening in the middle called pupil. The pupil appears black because no light is reflected from it.
The iris regulates the amount of light entering the eye. It regulates the light by adjusting the size of the pupil.The eye lens is a convex lens made of a transparent jelly - like proteinaceous material. The eye lens is hard at the middle and gradually becomes soft towards the outer edges. The eye lens is held in position by ciliary muscles. The ciliary muscles help in changing the curvature and focal length of the eye lens.
The inner back surface of the eye ball is called retina. It is a semi-transparent membrane which is light sensitive and is equivalent to the screen of a camera.
The light sensitive receptors of the retina are called rods and cones. When light falls on these receptors they send electrical signals to the brain through the optic nerve.
The space between the retina and eye lens is filled with another fluid called vitreous humour.
The light coming from an object enters the eye through cornea and pupil. The eye lens converges these light rays to form a real, inverted and diminished image on the retina. The light sensitive cell of the retina gets activated with the incidence of light and generates electric signals. These electric signals are sent to the brain by the optic nerves and the brain interprets the electrical signals in such a way that we see an image which is erect and of the same size as the object.
The process by which the ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina is called the accommodation of the eye.
The ability of the eye to focus objects lying at different distances is called the power of accommodation of the eye.
The distance between the near point and the far point is called the range of vision.
Colour vision is possible only through cones of the retina which are stimulated only in bright light. You cannot make out the red, violet or purple flowers in a garden on moonlight, because then only rods function and not cones