![]() ![]() It is the farthest point up to which the eye can see objects clearly. □The far point of a normal eye is infinity. The focal length of the eye lens cannot be decreased below this minimum limit of object distance. □ The minimum distance of the object by which clear distinct image can be obtained on the retina is called least distance of distinct vision. The ability of the eye lens to adjust its focal length accordingly as the object distances is called power of accommodation. This enables you to see the nearby objects clearly. For this, the ciliary muscles contract to increase the curvature and thereby decrease the focal length of the lens. To see the nearby objects clearly, the focal length of the lens should be shorter. ![]() This enables you to see the distant object clearly. For this, the ciliary muscles relax to decrease the curvature and thereby increase the focal length of the lens. To see a distant object clearly, the focal length of the lens should be larger. It is the ciliary muscles that can modify the curvature of the lens to change its focal length. It is made possible because the focal length of the human lens can change i.e., increase or decrease, depending on the distance of objects. Have you wondered why the eye is able to focus the images of objects lying at various distances? Its function is (i) to prevent front part of the eye ball from collapsing with the change in atmospheric pressure (ii) to keep the cornea moist. L) Aqueous humour: It is a watery, saline fluid, filling the part of the eye between the cornea and the crystalline lens. Its function is (i) to prevent the eye ball from collapsing due to change in atmospheric pressure (ii) in focussing the rays clearly on the retina. K) Vitreous humour: It is a dense jelly like fluid, slightly grey in colour, filling the part of eye between crystalline lens and retina. This is done by increasing or decreasing the diameter of pupil. The function of iris is to control the amount of light entering in eye. The colour of eyes depends upon colour of pigment. These muscles can increase or decrease the diameter of the pupil. It has tiny muscles arranged radially around the pupil. It has a tiny hole in the middle and is commonly called pupil. J) Iris: It is a circular diaphragm suspended in front of the crystalline lens. Its function is to alter the focal length of crystalline lens so that the images of the objects, situated at different distances, are clearly focussed on the retina. When these muscles relax, they increase the focal length of the crystalline lens and vice versa. I) Ciliary muscles: It is a ring of muscles which holds the crystalline lens in position. Its function is to focus the images of different objects clearly on the retina. It is held in position by a ring of muscles, commonly called ciliary muscles. H) Crystalline lens: It is a double convex lens made of transparent tissues. Any image formed on this spot is not visible. ![]() It has no nerve endings and hence, is insensitive to the light. G) Blind spot: It is a region on the retina, where the optic nerve enters the eye ball. Its function is to very clear image by sending a large number of optical pulses to brain. It has high concentration of nerve endings and is slightly raised as well as slightly yellow in colour. These pulses are then sent to the brain through optic nerve.į) Yellow spot: It is a small area facing the eye lens. The function of retina is to receive the optical image of the object and then convert it to optical pulses. On the retina are two important areas which we will discuss separately. These nerve endings on the retina are sensitive to visible light. The nerve endings form a hemi-spherical screen called retina. Its function is to carry optical message (visual messages) to the brain.Į) Retina: The optic nerve on entering the ball, spreads like a canopy, such that each nerve and attaches itself to the choroid. Its function is to darken the eye from inside and, hence, prevent any internal reflection.ĭ) Optic Nerve: It is a bundle of approximately 70,000 nerves originating from brain and entering eye ball from behind. i.e., to allow the light to enter in the eye ball.Ĭ) Choroid: It is a grey membrane attached to the sclerotic from the inner side. Its function is to act as a window to world. Its function is to house and protect vital internal parts of eye.ī) Cornea: It is the front bulging part of the eye. It is made of white tough fibrous tissues. The essential parts of a human eye are shown in figure.Ī) Sclerotic: It is the outermost converging of the eye ball. The human eye is like a camera having a lens on one side and a sensitive screen called the retina on the other. The most important part of our eyes is a convex lens inside it that is made of living cells. Our eyes enable us to see the beautiful world around us. ![]()
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