Tuesday, April 24, 2012

The Human Eye

        The eyes are a part of the sense organs that give human beings and most other animals the most accurate and detailed information about heir surroundings. Our eye is a sphere measuring about 2.5 cm in diameter. It rests in bony socket in the skull and can move in all directions due to the actions of the six ocular muscles.

          Eyes work on the principle of a photographic camera. The light rays form the object enters the pupil and are focused by the lens on the retina. Before the light enters the pupil, it passes through the cornea and aqueous humor. Lens forms an inverted reduced image of the object on the retina. From the image part of the eye, signals are sent to the brain by the optic nerves. The brain makes the correct and real image of the object and perceives depth and distance. The sensitive cells of the eyes are called rods and cones. The number of these cells is about 130 million. Rods are sensitive to light while cones are sensitive to colors. The two images produced by tow eyes are combined by the brain as one. The ability of the brain to form one image from the images of the tow eyes is called binocular vision.

Main parts of the eye

·       Lachrymal: this is the tear gland of the eye which produces tears. The tears clean the eyes.
·       Iris: it makes the pupil contract or dilates to control the amount of light that enters the eye.
·       Suspensory ligaments: lens is covered with a thin capsule which is connected to ciliary body by a soft ligament.
·       Lens: this is a soft and transparent convex lens which forms the image of the object onto the retina.
·       Vitreous humor: it is a jelly type transparent fluid.  
·       Aqueous humor: water like liquid.
·       Cornea: transparent part in the centre of the eye ball.
·       Choroids layer: black colored soft layer which stops the spread of light.
·       Retina: light sensitive screen on which image of the object is formed.
·       Optic nerve: this carries the information of the image to the brain.
Nature has provided us two eyes which give the correct estimate
of distance, depth and solid nature of the objects.
The Parts of Human Eye