How Do Eyes See?
We all see with our eyes. The shape of the eye is spherical. The black portion of the eye is known as cornea. There is a small circular opening in cornea called the pupil. Through this opening, light enters the eye. Behind this is the iris, the amount of light entering the eye is controlled by iris. Behind this is convex lens. A screen is located in the rear part of the eye which is called retina. The image of any object seen by the eye is formed on retina. The retina consists of large number of cones and rods which are sensitive to colours. The optic nerves connect the retina to the brain. A fluid known as ‘vitreous humar’ lies between the lens and retina. There is also another type of fluid known as ‘aqueous humor’ lies between the pupil and lens. The white part of the eye is 
called sclera. Now the question arises how do eyes see? Light rays from the object fall on the cornea of our eyes. These light rays pass through the lens and make an inverted image of the object on the retina. This image reaches the brain by the optic nerves in the form of electrical signals. The brain again inverts the image and the image becomes erect. That is how we see the objects. This process is very fast. The image of an object keeps on the retina for 1/16 second after the object has been removed from the sight. If two actions take place in 1/16 second they appear to be continuous to the eyes. The iris of the eye contract in more light and expands in dim light. We differentiate the colours with the help of cores of the retina. And in dim light we see with the help of rods.
