How the Human Eye Works

The eyes are organs of the visual system. The eye has a number of components that include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid, and vitreous. Eyes detect light and convert it into electro-chemical impulses in neurons.

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Generally, your eyes are at work from the moment you wake up to the moment you close them to go to sleep. They take in tons of information about the world around you such as shapes, colors, movements, and more. Then they send the information to your brain for processing so the brain knows what’s going on outside of your body.

Parts of the Eyes

  • Cornea: clear front window of the eye that transmits and focuses light into the eye.
  • Iris: colored part of the eye that helps regulate the amount of light that enters
  • Pupil: dark aperture in the iris that determines how much light is let into the eye
  • Lens: transparent structure inside the eye that focuses light rays onto the retina
  • Retina: nerve layer that lines the back of the eye, senses light, and creates electrical impulses that travel through the optic nerve to the brain
  • Macula: small central area in the retina that contains special light-sensitive cells and allows us to see fine details clearly
  • Optic nerve: connects the eye to the brain and carries the electrical impulses formed by the retina to the visual cortex of the brain
  • Vitreous: clear, jelly-like substance that fills the middle of the eye

Accordingly, you can check out different parts of the eye by looking at your own eye in the mirror. Some of the eye’s parts are easy to see but some parts cant be seen.

Alt text = Structure of an human eye
Structure of a human eye

The size of eyes is as big as a ping pong ball

In the meantime, the eye is about as big as a ping-pong ball and sits in a little hollow area (the eye socket) in the skull. For the most part, the eyelid protects the front part of the eye. In particular, the lid helps keep the eye clean and moist by opening and shutting several times a minute. This is called blinking, and it’s both a voluntary and involuntary action, meaning you can blink whenever you want to, but it also happens without you even thinking about it.

The eyelid also has great reflexes, which are automatic body responses, that protect the eye. When you step into bright light, for example, the eyelids squeeze together tightly to protect your eyes until they can adjust to the light. And if you flutter your fingers close but not too close to your eyes, you will feel your eyes blink. So then your eyelids shut automatically to protect the eye from possible danger. For the most part, don’t forget eyelashes. Together with they work with the eyelids to keep dirt and other unwanted stuff out of your eyes.


The white part sclera is the eyeball. The sclera is a tough material and has the important job of covering most of the eyeball. Such as think of the sclera as your eyeball’s outer coat. Look very closely at the white of the eye, and you’ll see lines that look like tiny pink threads. Generally, these are blood vessels, the tiny tubes that deliver blood, to the sclera.


This is a transparent dome, sits in front of the colored part of the eye. Therefore the cornea helps the eye focus as light makes its way through. It is a very important part of the eye, but you can hardly see it because it’s made of clear tissue. Similarly like clear glass, the cornea gives your eye a clear window through to view the world.

Iris Is The Colorful Part In The Eyes


Behind the cornea are the iris, the pupil, and the anterior chamber. The iris is the colorful part of the eye. In this case, the iris has muscles attached to it that change its shape. In particular, this allows the iris to control how much light goes through the 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. Such as to see how this works, use a small flashlight to see how your eyes or a friend’s eyes respond to changes in brightness. The pupils will get smaller when the light shines near them and they’ll open wider when the light is gone.

Anterior chamber

The anterior chamber is the space between the cornea and the iris. This space is filled with a special transparent fluid that nourishes the eye and keeps it healthy.

Light, Lens, Action

These next parts are really cool, but you can’t see them with just your own eyes. Doctors use special microscopes to look at these inner parts of the eye, such as the lens. After light enters the pupil, it hits the lens. Accordingly, the lens sits behind the iris and is clear and colorless. Generally, the lens’s job is to focus light rays on the back of the eyeball, a part called the retina. 

Especially the lens works much like the lens of a movie projector at the movies. Next time you sit in the dark theater, look behind you at the stream of light coming from the projection booth. This light goes through a powerful lens, which is focusing the images onto the screen, so you can see the movie clearly. In the eye’s case, however, the film screen is your retina.


Your retina is in the very back of the eye. It holds millions of cells that are sensitive to light. The retina takes the light the eye receives and changes it into nerve signals so the brain can understand what the eye is seeing.

A Muscle Makes It Work

Ciliary body: The lens is suspended in the eye by a bunch of fibers. Such as these fibers are attached to a muscle called the ciliary body. It has the amazing job of changing the shape of the lens. That’s right — the lens actually changes shape right inside your eye! Try looking away from your computer and focusing on something way across the room. Even though you didn’t feel a thing, the shape of your lenses changed. When you look at things up close, the lens becomes thicker to focus the correct image onto the retina. When you look at things far away, the lens becomes thinner.

Vitreous body: The biggest part of the eye sits behind the lens and is called the vitreous body. The vitreous body forms two-thirds of the eye’s volume and gives the eye its shape. It’s filled with a clear, jelly-like material called the vitreous humor. Ever touch toy eyeballs in a store? Sometimes they’re kind of squishy — that’s because they’re made to feel like they’re filled with vitreous humor. In a real eye, after light passes through the lens, it shines straight through the vitreous humor to the back of the eye.

Rods and Cones Process Light

Rods and cones: The retina uses special cells called rods and cones to process light. Just how many rods and cones does your retina have? There are about 120 million rods and 7 million cones in each eye.

Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods can’t tell the difference between colors, but they are super-sensitive, allowing us to see when it’s very dark.

Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light. The retina has three types of cones. Each cone type is sensitive to one of three different colors such as red, green, or blue to help you see different ranges of color. Together, these cones can sense combinations of light waves that enable our eyes to see millions of colors.


Rods and cones process the light to give you the total picture. You’re able to see that your friend has brown skin and is wearing a blue hat while he tosses an orange basketball.

Sometimes someone’s eyeball shape makes it difficult for the cornea, lens, and retina to work perfectly as a team. When this happens, some of what the person sees will be out of focus.

To correct this fuzzy vision, many people, including many kids, wear glasses. Glasses help the eyes focus images correctly on the retina and allow someone to see clearly. As adults get older, their eyes lose the ability to focus well and they often need glasses to see things up close or far away.

Connections of Optic Nerve To The Brain

Optic nerve: The optic nerve is the great messenger in the back of your eye. The rods and cones of the retina change the colors and shapes you see into millions of nerve messages. Then, the optic nerve carries those messages from the eye to the brain!

The optic nerve serves as a high-speed telephone line connecting the eye to the brain. When you see an image, your eye sends an instant message to your brain with a report on what you are seeing.

Lacrimal glands

The eye has its own special bathing system such as tears. Above the outer corner of each eye are the lacrimal glands, which make tears. Every time you blink your eye, a tiny bit of tear fluid comes out of your upper eyelid. It helps wash away germs, dust, or other particles that don’t belong in your eye.

Tears also keep your eye from drying out. Then the fluid drains out of your eye by going into the lacrimal duct (the other name is tear duct). You can see the opening of your tear duct if you very gently pull down the inside corner of your eye. When you see a tiny little hole, you’ve found the tear duct.


Your eyes sometimes make more tear fluid than normal to protect themselves. This may have happened to you if you’ve been poked in the eye, if you’ve been in a dusty or smoking area, or if you’ve been near someone who’s cutting onions.

Your eyes got a message from your brain to make you cry, and the lacrimal glands made many, many tears. And also when you felt sad, scared, or upset?

Most common vision problems of the eyes

The most common problems with vision are nearsightedness (myopia), farsightedness, (hyperopia), a defect in the eye caused by nonspherical curvature (astigmatism), and age-related farsightedness (presbyopia), according to the National Eye Institute.

In short, the leading causes of blindness are cataracts (clouding of the lens), age-related macular degeneration (deterioration of the central retina), glaucoma (damage to the optic nerve), and diabetic retinopathy (damage to retinal blood vessels). Other common disorders include amblyopia (“lazy eye”) and strabismus (crossed eyes).

Tips to keep your eyes healthy

Your eyes do some great things for you, so take care of them.

  • Eat a healthy, balanced diet. Your diet should include plenty or fruits and vegetables, especially deep yellow and green leafy vegetables. Eating fish high in omega-3 fatty acids, such as salmon, tuna, and halibut can also help your eyes.
  • Maintain a healthy weight. Being overweight or having obesity increases your risk of developing diabetes. Having diabetes puts you at higher risk of getting diabetic retinopathy or glaucoma.
  • Get regular exercise. Exercise may help to prevent or control diabetes, high blood pressure, and high cholesterol. These diseases can lead to some eye or vision problems. So if you exercise regularly, you can lower your risk of getting these eye and vision problems.

Sunglasses Benefits for eyes

  • Wear sunglasses. Sun exposure can damage your eyes and raise your risk of cataracts and age related macular degeneration. Protect your eyes by using sunglasses that block out 99 to 100 percent of both UV-A and UV-B radiation.
  • Wear protective eye wear. To prevent eye injuries, you need eye protection when playing certain sports, working in jobs such as factory work and construction, and doing repairs or projects in your home.
  • Wear sunglasses as too much light can damage your eyes and cause vision problems later in life. For instance, a lens could get cloudy, causing a cataract. A cataract prevents light from reaching the retina and makes it difficult to see.


  • Avoid smoking. Smoking increases the risk of developing age-related eye diseases such as macular degeneration and cataracts and can damage the optic nerve.
  • Know your family medical history. Some eye diseases are inherited, so it is important to find out whether anyone in your family has had them. This can help you determine if you are at higher risk of developing an eye disease.
  • Know your other risk factors. As you get older, you are at higher risk of developing age-related eye diseases and conditions. It is important to know you risk factors because you may be able to lower your risk by changing some behaviors.
  • If you wear contacts, take steps to prevent eye infections. Wash your hands well before you put in or take out your contact lenses. Also follow the instructions on how to properly clean them, and replace them when needed.
  • Also give your eyes a rest. If you spend a lot of time using a computer, you can forget to blink your eyes and your eyes can get tired. To reduce eyestrain, try the 20-20-20 rule: Every 20 minutes, look away about 20 feet in front of you for 20 seconds.

For the most part, it is important to identify and treat eye diseases as early as possible. You should get your eyes checked as often as your health care provider recommends it, or if you have any new vision problems. And just as it is important to keep your body healthy, you also need to keep your eyes healthy. The eyes you have will be yours forever treat them right and they’ll never be out of sight!

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