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A Detailed Study of the Parts of the Human Eye and Their Working

Parts of the Human Eye
This article gives you information on the parts of the human eye, its functions, and the working strategy of the eye as a whole.
Kalpana Kumari
Last Updated: Dec 21, 2017
Our eyes are the doorway to the external environment, and clearly, the most important of the sense organs. They play a pivotal role in our day-to-day existence. The eye receives light from the outside world, and converts it into electrical signals that are transported to the brain and perceived as an image. So what are the parts of the eye? In the coming sections, we will learn about the human eye, its various parts, and how these parts work in collaboration to enable us to see the world around us.
Main Parts of the Human Eye
The sclera is the white part of the eye that surrounds the cornea. It is made up of fibrous tissues, and provides protection to the inner parts of the eye. This is the tissue that is commonly called the white of the eye.
The cornea is the transparent tissue at the front of the eyes through which light coming from an object enters the eye. It also helps in focusing the light on the retina.
Aqueous Humor
It is a clear transparent fluid that fills the space between the cornea and the eye lens. It also supplies nutrients and oxygen to these parts.
The iris is a ring of muscles in the central part of the eye, that is helpful in regulating the amount of light entering the eye by controlling the size of the pupil.
This is an opening in the center of the iris through which light passes and falls on the eye lens. Its size is controlled by the iris.
Eye Lens
The lens of the eye is situated directly behind the pupil. It helps in focusing the light on the retina. The eye lens is capable of changing its shape so as to enable us to see objects near and far.
Ciliary Muscles
This is a ring-shaped tissue that holds and controls the movement of the eye lens, and therefore, helps in controlling the shape of the lens.
Vitreous Humor
It acts as a filler and covers the space between the eye lens and retina. It also provides protection to the lens. It makes up for about two-thirds of the total volume of the eye, and is composed mainly of water.
It is a membrane responsible for converting the light falling on it into electrical impulses that can be sent to the brain. The retina contains light-sensitive photoreceptor cells called rods and cones. The rods help in black and white vision and for seeing in dim light, while the cones help in daytime and color vision.
Optic Nerve
It is a bundle of nerve fibers that serve as a cable that connects the eye to the brain. This optic nerve helps in transmitting signals from the retina to the visual center of the brain.
Yellow Spot or Macula
Situated at the center of the retina, this yellow spot helps in absorbing excess light that enters the eye. The macula is responsible for our reading vision, and helping us to see objects right in front of us.
The eyelids help in the protection and lubrication of our eyes. They also help in controlling the amount of light falling onto our eyes.
Muscles of the Eye
The eyeball is held in its place by the help of several eye muscles. The eye muscles are responsible for the up and down, as well as the left and right movement of the eye.
Working of the Human Eye
1. When we look at an object, the light falling on it is reflected towards our eyes, and it enters the eye through the transparent layer of cornea, which helps in focusing the light.
2. Light then passes through the moisture-containing aqueous humor and reaches the central opening called the pupil, which with the help of the iris expands or contracts to regulate the amount of light passing through it.
3. The light coming through the pupil passes to the eye lens, which helps in adjusting and focusing the light on the retina. It does so by changing its shape, depending upon whether the light is coming from a distant or a close-by object.
4. The focused light then passes through the vitreous humor and is finally projected on the epiretinal membrane containing the photoreceptor cells. The rods and the cones of the retina convert the light rays into electrical impulses.
5. These electrical signals are transmitted by the optic nerve to reach the visual centers in the brain. The brain interprets and perceives these signals as an image.
Interesting Facts
The eyes are said to be the ultimate marvel of biological evolution, and are often compared to the brain in terms of complexity. Here are some fascinating facts about the human eye:

  • Our eyes can process 36,000 bits of information in an hour's time.
  • The human eye goes on to blink at an average of 4,200,000 times every year.
  • It's impossible to sneeze with your eyes open.
  • The human eye can see the light of a candle that has been placed 14 miles away, under suitable conditions.
  • Human eyes are capable of detecting over 10 million colors.
  • The eye of a human can distinguish 500 shades of the color gray.
  • The cornea is the only living tissue that does not contain any blood vessels.
  • All babies are colorblind when they are born.
  • The color of the iris determines whether our eyes look black, blue, green, brown, or gray.
  • The lens in our eye is quicker than any camera lens invented till date.
  • During an average lifespan, a human would see around 25 million images around him.
  • The muscles of the eyes are the most active ones in the whole body.