Human Eye

All About the Human Eye Diagram, Parts of the Eye and Their Functions. In this article, we will be learning about the human eye, parts of the eye with their functions, how does the human eye work step by step and many amazing facts about the eye for kids.

➤ Why should we learn about the eye diagram?

If we know about all the parts of our eye and their function, we’ll be able to understand how our eye works in a better way.
human_eye
Human Eye [pic via Google]

➤ What is the eye?

The eye is the organ of sight. It is a very complex, little sensory organ of human body. As you know each organ has a specific function, and in this case the eye helps us to see the world around us.

➤ Human Eye Diagram

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Human Eye Diagram [pic:nei.nih.gov]

➤ What are the Three Layers of the Human Eye?

  1. The Outer Layer – The Cornea and Sclera
  2. The Middle Layer – Iris, The Choroid, and The Ciliary Body
  3. The Inner Layer:-The Retina

➤ What are all parts of the human eye and their functions?

➤ Sclera

The Sclera is a strong outer white part of the eye . It is also known as the “white”. The sclera provides the eye with structural strength and protection.

➤ Cornea 

The cornea is the transparent part of the eye that covers the front portion of the eye. It covers the pupil, iris and anterior chamber.

There are no blood vessels present in the cornea, but instead of blood vessels it contains many nerve endings that make it extremely sensitive. That is why it is so painful when we get an eyelash in our eye.

➤ Functions of the cornea

The cornea helps the eye in several ways: The cornea protects the eye from germs, dust, and other harmful matter with the help of eyelids, the eye socket, tears, and the sclera.

It acts like a window that controls and focuses the entry of light into the eye. It contributes around 70% of the eye’s total focusing power.

➤ Anterior Chambers

The anterior chamber is the front part of the eye between the cornea and the iris.

➤ Posterior Chambers 

The posterior chamber is between the iris and lens. Posterior chamber is an important structure involved in production and circulation of a watery fluid known as the aqueous humor, or aqueous.

➤ Iris of the Eye 

Iris Definition –  The iris is the colored part of the eye that surrounds the pupil.

Iris function – It regulates the amount of light that enters the pupil by contracting and stretching. This way It prevents the retina from receiving excess light and getting damaged.

For example, if you go into a dark room, you will notice that your pupil will get wider because you need lots of light to see. But if you go to a sunny area your pupil will get smaller because you don’t need much light. You can do this experiment with the help of a flashlight.

Do you know? The color of the Iris depends on how much pigment you have. If you have very little pigment your Iris color will be blue and if you have lots of pigment your Iris color will be brown to black.

➤ Pupil

The pupil is the black circle in the center of the iris, which is really an opening in the iris, and it lets light enter the eye. It’s size is controlled by the relaxing and contracting of the iris. In bright light the pupil shrinks and grows in low light intensity.

Do you know? The pupil appears black because the light rays entering the pupil is absorbed by the tissues inside the eye and is not reflected back.

➤ Lens

The lens of the eye focuses light and allows you to see. The lens is a transparent biconvex intraocular tissue that exists behind the pupil. The main function of the lens is to focus light rays onto the retina.

The lens obtains nutrients from the fluid, aqueous humour because it does not have any blood supply. Waste products are removed through these fluids as well.

➤ Vitreous Humor

Vitreous Humour (Chamber) is the transparent, colorless mass that fills the rear two-thirds of the eyeball, between the lens and the retina.

➤ Retina

The retina is the light-sensitive tissue at the back of the eye. It communicates directly to the brain. The retina receives light from the lens, converts it into electrical impulses and sends these signals to the brain for visual recognition.

➤ Macula

The macula, a small part which is located in the center of the retina that gives central vision.

➤ Human Eye Anatomy

human_eye
Human Eye Image [pic:wikimedia]

➤ How does the human eye work step by step?

human_eye

Following are the step-by-step explanation of how the eye works to provide us the vision.

➤ First, light rays enter the eye through the cornea, the clear front “window” of the eye. The dome shaped cornea bends light to help the eye focus.

➤ From the cornea, the light passes through an opening called the pupil. The amount of light passing through is controlled by the iris, or the colored part of your eye.

➤ Next, light passes through the lens, the transparent structure inside the eye. The lens works together with the cornea to focus light correctly onto the retina.

➤ Finally, when light hits the retina (innermost part), special cells called photoreceptors turn the light into electrical signals.

➤ These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.

➤ What is Blind Spot?

This is a small area of the retina where the optic nerve connects. In this area there are no light-sensitive cells i.e. no rods and cones. Due to which the retina can not see at that spot. This is called a Blind Spot.

➤ What Are Tear Glands?

The tear gland located above each eyeball and inside your upper eyelid. This gland is responsible for making a fluid that is mostly salt and water (tears) to keep the surface of your eyeball clean and moist. It also protects your eye from damage.

➤ Fun Facts About Human Eye For Kids

FACT 1 ➤ Iris scanning is more secure than fingerprints because our iris has 256 unique characteristics and the fingerprint has just 40.

FACT 2 ➤ Newborn babies don’t produce tears. They only make crying sounds, but no tears come out of their crying eyes. Tears in the baby’s eye start to produce when the baby is about 1-3 months old. Because their tear ducts haven’t developed yet.

FACT 3 ➤ The shark cornea and human cornea are identical. The shark has even been used in human eye surgery!

FACT 4 ➤ The length of our eyes are about 1 inch across and weigh about 0.25 ounce

FACT 5 ➤ Our eyeballs stay the same size forever but our nose and ears continue to grow.

FACT 6 ➤ Eyes are the second most complex organ after the brain. Eyes consists of more than two million working parts.

FACT 7 ➤ Dolphins can sleep with one eye open and one half of their brain awake. It can control their breathing and at the same time it keeps a constant look out for predators.

Dolphins need to keep conscious even when they are sleeping. Because they have to actively decide when to breathe, and so they must be continually conscious to breathe. This is because their breathing is not automatic like humans.

If dolphins went into a deep sleep, they would stop breathing and drown. This type of sleep is known as unihemispheric sleep.

FACT 8 ➤ Our retinas see the world upside down but the brain flips the image around for us to see the world correctly.

FACT 9 ➤ An ostrich’s eye is bigger than its brain. An ostrich eye is the largest eye of any living LAND animal on the planet.

FACT 10 ➤  Giant squid have the largest eye in the entire animal kingdom. It’s size is 27cm (11in) in diameter like a soccer ball.

FACT 11 ➤  Do you know, Chameleons can move their eyes in two directions at once.

FACT 12 ➤   The human eye can detect more than 10 million different types of colors.

FACT 13 ➤  The world’s most common eye colour is brown.

FACT 14 ➤ The average person blinks 12 times a minute. Scientists have estimated that we blink between 20,000 and 30,000 times per day on average.

FACT 15 ➤ Dogs cannot distinguish between GREEN and RED. Humans have three different color sensitive cone cells in their retina i.e. red, green and blue. But dogs have only two, yellow and blue. That is why dogs can’t distinguish green, yellow or red objects. Useful Resources: Eye

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