Eye biology details
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The eye is an important organ of sight of the body having a very complicated structure. This organ functions best, when all the parts of its structure are working well.

The eye is shaped like a ball which is moved by muscles attached to it. It has a tough, outer, white coating, called the sclera, which covers the whole eye, except the cornea. Inside the sclera are contained the essential parts. These essential parts are the following.

Cornea: It is the transparent, dome-shaped, front part of the eye. It is a powerful refracting surface, providing most of the eye’s optical power. The cornea is unique among the eye parts, as it has no blood vessels and therefore can be transplanted. The cornea has numerous nerve endings, making it the most sensitive part of the eye. The tear glands keep the cornea moist and clean.

Pupil: In the centre of the cornea is a black hole known as the pupil, through which light enters. The pupil controls the amount of light that should be entering the eye. More or less than the necessary amount of light, may not produce the correct vision.

Iris: It is the pigmented part, which decides the color of your eyes. It does not allow light to pass through. It is the iris muscles, which changes the size of the pupil

Lens: A little way inside the cornea is the lens, which focuses the light.

Eye chambers: The lens divides the eye into two unequal chambers called the front or the anterior chamber and the rear or the posterior chamber. The smaller front chamber contains a watery fluid, known as the aqueous humor and the larger rear chamber contains a jelly like substance called the vitreous humor.

Choroid: The sclera is lined inside by a pigmented membrane, the choroids.

Retina: The choroid in turn is lined at the rear half of the eyeball by the almost transparent parent retina. The retina is to the eye what a film is to a camera. The retina contains millions of very sensitive photoreceptor cells, called rods and cones that are connected to the brain by optic nerves. Rods and cones play a major part in enabling you to see.

Protective features

Additionally the eye is provided with parts which protect it. Among these are the eyelids and the eyelashes, which function as barriers to the entry of any foreign objects. The eyelids have another important function of spreading tears on the eye surface. Tears are a salty fluid, produced by lacrimal glands located under the upper eyelids.

Secretions by some small glands and parts and tears produce the tear film which keeps the eye surface moist. The tear film is important to keep the cornea transparent and uninfected. The eyes are kept clean by a continuous supply of tears. Tears contain antibodies which help prevent infection.


The entire eye is situated in a bony structure, which protrudes beyond the eye surface. This structure is called the orbit. The orbit protects the eye and at the same time allows it to move freely.

Process of seeing

Light falling on the eye is allowed, in the requisite mount, by the pupil to enter it. The lens brings these light rays to a focus on the retina by using small eye muscles, known as the ciliary body. These ciliary muscles allow the lens to change its shape so that the light is always focused on the retina. The sensitive rods and cones on the retina absorb these light signals and convert them into electrical impulses. The optic nerves carry these electrical impulses to the brain to produce the vision that you see. The eye is always, adjusting the amount of light to be let in, focusing and instantly transmitting signals to the brain.

The image on the retina is always upside down, but it is the processing done by the brain which makes us see things right side up.

3-D vision

Because humans have two eyes, each eye catches a different view of the object being viewed. This is called stereoscopic vision. The brain processes signals received from both eyes to produce a three dimensional vision which has depth. This 3-D vision allows us to judge distances and depth better.

Sight is our most important sense. It is estimated that almost 80% of our learning takes place through the eyes. Eyes are therefore precious. An understanding of how the eye works and its importance will help you in maintaining good eye health.

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