Human Eye: Definition, Parts, Functions, Structure, and Diagram

In this blog, we will learn about the human eye, its structure, and its functions. An Eye is the most important sense organ that helps us in viewing things. We see things only when light coming from them enters our eyes.

The World is beautiful and full of colors. Green is the color of plants, the color of nature. Blue is the color of water and 2/3 of our earth is covered with water. Could you have ever thought of this beauty, if you had never seen that? Sense of sight is one of the most important senses.

Let us learn what is inside our Eyes. The human eye is roughly spherical in shape. The outer coating of the human eye is white in color. It is tough so that it can protect the interior of the eye from accidents.

Human eye diagram
Human Eye Diagram

The transparent spherical membrane over the bulge in the front of the eyeball is called Cornea. Between the cornea and the lens, there is a dark muscular structure or diaphragm called Iris. Iris has a small hole in it which is called a Pupil. Iris gives distinctive color to the eye. If the iris is green then the eye looks green. If the iris is grey then the eye looks grey.

Iris also controls the amount of light entering into the eyes by controlling the size of the Pupil. If the light is dim then the pupil will open wide or dilate to allow more light to enter the eye and if the light is bright then the pupil will open less or contract so that less light enters into it.

Behind the pupil of the eye, there is a lens that is thicker at the center i.e. it is a convex lens. It is the most sensitive part of the eye. The lens focuses the light on the back of the eye. The lens is held in its position by the ciliary muscles.

The layer on the back of the human eye is called Retina. It works like a screen where the lens focuses the light and the image of the object is formed. The Retina contains several nerve fibers and blood vessels.

There are two kinds of nerve cells:-
1) Cones: Cones are sensitive to bright light and also sense color.
2) Rods: Rods are sensitive to dim light.

Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve. The point at which the optic nerve leaves the eye has no sensory cells, so no vision is possible at that spot. This spot is called ‘The Blind Spot’.

Near Point and Far point of the eye: The nearest point up to which the human eye can see clearly is called the near point. It is approximately 25 cm for a normal human eye. The farthest point up to which the eye can see is the far point. It is infinite for normal vision.

The minimum distance up to which the human eye can see objects distinctly is called the least distance of distinct vision and it is denoted by D. It varies with age.

Persistence of Vision:- The impression of an image does not vanish immediately from the Retina. It persists there for about 1/16th of a second. If still images of a moving object are flashed on the eye at a rate faster than 16 images per second, then the human eye perceives this object as moving.

Eye Disorders

1. Myopia (Farsightedness)

Some people can see objects close to them clearly but cannot see distant objects. They need a concave lens to see the distant objects clearly.

2. Hypermetropia (near-sightedness)

Some people cannot see close objects clearly but can see distant objects. They need a convex lens to see nearby objects.

3. Cataract

Sometimes, particularly in old age, eyesight becomes foggy. It is due to the eye lens becoming cloudy. When it happens, patients are said to have CATARACT. There is a loss of vision. It is possible to treat this disorder. The opaque lens is removed and a new artificial lens is inserted.

Visually challenged people

  1. People who have poor vision or cannot see are said to be visually challenged.

Visually challenged people can read or write through a special system called BRAILLE SYSTEM. It was developed by Louis Braille in 1821.

Caring for your eyes

  1. Wear sunglasses whenever you go out in the sun to protect your eyes from the harmful ultraviolet radiation of the sun.
  2. Wash your eyes frequently with cold water.

Read More: Human Skeletal System – Types of Bones | Body Movements

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