Human eye

               Human eye

 It is the most valuable and sensitive sense organ. It is a remarkable optical instrument. 

Structure of the eye

It shows the different parts of the eye. Light enters the eye through a curved front surface cornea. It passes the pupil which is the central hole in the iris. The size of the pupil can change under muscular action of the iris. The light is further focussed by the eyelens on the retina. The retina is a film of nerve fibers covering the curved back surface of the eye. The retina contains light sensitive cells called rods and cones. Rods are sensitive to intensity of light while cones are sensitive to colours. These cells change light energy into electrical signals which send message to the brain via optic nerves. 

Action of the eye

The transparent structures like cornea, aqueous humour, eyelens and vitreous humours together constituents a single converging lens. As the rays from an object enter the eye, they suffer refractions on passing successively through these structures and get converged. A real and inverted image is formed on the retina. The light sensitive cells of retina get activated and generate electrical signals that are sent to the brain through the optic nerves. Our brain translates the inverted image into an erect image.