explain structure of human eye?
The Shape of the eye is roughly spherical with an average diameter of around 2.3 cm. The outer part of the eye is quite tough and white in colour. This white part of the eye is known assclera.The transparent, front outer covering of the eye is known as thecornea. Behind the cornea, there is a colored membrane known as theiris. It regulates the amount of light entering the eye. It also gives colour to the eye. In the iris, there is a variable sized, black circular opening known as thepupil. Its size is controlled by the iris. It appears to be black in colour because most of the light entering it is absorbed by the tissues, which are present in the pupil.
The size of the pupil depends on the brightness of light. It opens and closes in order to regulate and control the amount of light entering the eye. When we enter a dimly lit room, it takes the iris some time to expand the pupil to allow more light to enter the eye. For this reason, it takes us a few seconds to clearly see objects in a dimly lit room
Behind the pupil there is a lens which is thicker at the centre. It is made up ofliving cells. TwoCiliary muscleshold the lens within the eye-ball. The eye lens being convex in nature converges the light rays incident on it. Hence, it focuses the light falling on it on a thin layer of nerve cells called theretina. The retina is made up of a large number of nerve cells. Light falling on these nerve cells stimulate two kinds of sensitive cells known asconesandrods. Rods are sensitive to low light levels. Cones are sensitive to bright light, but they sense colours. Sensation felt by them is transmitted to the brain in the form of electrical signals through the optic nerve. This allows us to see.
The human eye is an organ that reacts to light and has several purposes. As a conscious sense organ, the mammalian eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors.