Dr. Kane Explains How Eyes Work

Welcome to the Cornea by Kane blog, your trusted source for an honest opinion about your eyes.

Recently, I had the privilege of teaching a bright group of 1st graders all about the eye. It was loads of fun and the class asked a bunch of really interesting questions. Their questions were so interesting, in fact, that I just have to share them. So today let’s head back to the classroom to learn how the eyes work, answer some fun questions, and dispel (or confirm) some common myths.


What are the parts of the eye?

The main parts of the eye are the eyelids, the sclera, the cornea, the iris, the lens, the retina, and the optic nerve. The eyelids are the outer protecting skin layer that act like protective windshield wipers. The sclera is the white part of the eye. It forms the wall and supporting frame for the eye.

The cornea is the clear central part of the eye that we look through. It is the window of the eye. The iris is the colored part of the eye that controls how much light comes in the eye. It acts like the shutter in a camera. The lens helps focus the light on the retina so the image is clear. The retina changes the light into a signal that can travel down the optic nerve and into the brain.  


How do our eyes work?

Our eyes work like a camera. Light and images enter the eye by passing through the cornea, the pupil, and the lens to be focused clearly on the retina. The retina layer of the eye is like the film in a camera. The retina processes the light image by changing it into a chemical signal and sending that signal down the optic nerve into the brain. In the brain, the signals are processed and assembled into what we see. 


Where does Color come from?

Color comes from light. Without light, everything is gray or dark (like at night). Light is made of all the colors traveling together (ROYGBIV). When light hits something, some of the light gets absorbed and some of the light bounces back to us (reflected). The color we see depends on what part of the light bounces back. Tomatoes for example absorb all the light colors except red, which bounces back into our eyes. 

The light that bounces back to us enters our eyes where it stimulates the retina (made of tiny little cones that process red, blue, and green) inside our eye. The retina receives the light and converts it into a signal that travels into our brain where we process it and then determine the color based on the signal pattern. 


Why do we have pupils?

The pupil is the circular dark space in your iris. The iris is the round brown/blue/green colored part of your eye and together they have a very very important job. The pupil controls how much light can get in the eye and it is always changing size based on how much light there is.

In a dark room, the pupil gets bigger (the iris dilates) to allow maximum light inside so you can see when there is only a little light. When you step outside, the pupil gets very small (the iris constricts) to allow only a little bit of the bright light to get in the eye. Both too much and too little light can make it hard to see and the pupil tries to help keep the amount of light going in the eye just right!


Is reading in the dark bad for our eyes?

How many times have we all heard our parents say that one? The answer is No! Reading in the dark does not hurt our eyes. It may be difficult to do, but it does not cause harm. When reading in the light, we use our central retina (made up of cones). The reason it is hard to read in the dark is because we use the peripheral part of the retina (made up of rods) to see in the dark. The rods just don’t have the fine resolution ability to allow us to read easily. 


Where does eye color come from?

Eye color comes from the part of the eye called the iris. The iris is a round muscle inside the eye and the color comes from specialized pigmented cells called melanocytes. These cells migrate into the eye and line the iris and this process can continue for a year and a half after birth. So many babies are born with gray colored eyes which change color during their first year of life.

The amount of pigment cells that migrate into the eye determines the color. If only a few pigment cells line the iris then your eyes will look blue but if a lot of them line the iris then your eyes will look brown. How many melanocytes migrate there is determined by your genes (DNA) which you get from your parents and grandparents. 


How many different colors of eyes are there?

There are 4 main categories of colors of the eye: blue, green, hazel (mixed) and brown. The part of the eye that gives it the color is called the iris. Eye color, however, is considered a range of color because people have different shades of blue, green, hazel and brown. So even though two people may each have blue eyes, the actual shade or color of blue may be different.

The color of your eyes is determined by your genes which you get from your parents and grandparents. Your genes control how your eyes develop and how much pigment or coloration they will have. So because everyone will have a slightly different amount of coloration there are infinitely many colors of the eye.


How do our eyes get watery?

When our eyes water, they are making tears (like when we cry). The eye has special glands that make these tears on the eye and in the eyelids. The body has ways of telling our eyes to make tears by sending signals to our brains along our nerves. So when we get hurt, laugh really hard, or feel sad, then our body will tell our eyes to make more tears which makes them watery. 


Why do our eyes itch sometimes?

Itching is caused when our body touches something it doesn’t like such as pollen or dust. When that happens, the mast cells release a chemical called histamine. Histamine is our body’s response that then attaches to the nerves in your eyes and sends signals to your brain. Those signals make your eyes feel like they burn or itch. The itching causes watering of the eyes which may help flush out the pollen or dust.

Unfortunately, the itching often leads to eye rubbing. Rubbing the eyes can cause the mast cells to release more histamine and make them itch more. So Never Rub Your Eyes! Rubbing your eyes can also cause damage to the cornea or front part of the eye so if your eyes itch a lot try to go see an eye doctor for help. 


Why do we blink?

Blinking is one of the most important protective features of our eyes. Blinking helps lubricate our eyes by spreading our tears around the surface so they stay moist. A healthy smooth tear surface on the eye is essential to having good vision. Blinking also helps brush away unwanted debris and bacteria that land on the eye, helping keep the eyes safe and healthy. Blinking is similar to breathing in that our bodies do it for us automatically (involuntarily) but we can also do it on purpose (voluntarily). 


How many times do I blink in a day?

The average person blinks about 15 times a minute…Let’s do the math! 15 x 60 = 900 times an hr. If you sleep similarly to my son, then you are awake from 6am till 8pm (about 14hrs). So 900 x 14 = 12,600 times a day!


Why do we have eyebrows?

Some people think we have eyebrows to help protect our eyes from things like sweat, rain, and dirt from running off our foreheads directly into our eyes. When something lands on your eyebrow generally it triggers a blink reflex as well which can protect your eye from debris. Eyebrows also play a role in communication. For example, we often raise them when we are surprised or push them down into a furrow when we are angry or sad. 


Is too much screen time bad for my eyes?

Yes and No. Spending some time in front of a screen is ok. Spending a lot of time looking at a screen can cause problems overtime. For young people, focusing on something up close for a long time can cause an eye muscle spasm or cramping which can make things blurry in the distance. Some doctors also believe that screen time can lead to higher amounts of nearsightedness or myopia.

Too much screen time is also related to an earlier question about dry eyes. When you stare at a screen your blink rate slows WAY DOWN. Basically you get into a staring contest with the device (and the device always wins). So for older people, spending too much time on a screen can lead to dry eyes.

Is the blue light from the screen harmful? No, the blue light from the screen is not currently thought to be harmful though it can make it harder to go to sleep at night. If you need to use electronic devices at night time, consider using a night mode setting so you don’t have trouble falling asleep. Click here to read an opinion from the American Academy of Ophthalmology about blue light in electronic devices. 


Do carrots really help my eyes?

Yes. Eating carrots as part of a balanced healthy diet is good for your eyes. Carrots contain beta-carotene which your body changes into Vitamin A. The cornea and the retina both need Vitamin A to function. The retina needs Vitamin A to process light and send the light signals to the brain and without it you would have difficulty seeing at night.

The cornea needs Vitamin A to stay clear and without it the cornea and your vision becomes cloudy. Our bodies do not make Vitamin A so we need to eat it as part of our diet and carrots are a good way to get it. No, eating a large amount of carrots will not give you super vision, though it might turn your skin slightly yellow/orange in color. 


Why are eyes so delicate?

In my opinion, the eyes are very delicate because of where they come from and the complicated job they have. The eyes grow out from our nervous system (brains) before we are born. This is a time when we are still developing and brain tissue is very delicate. The eyes probably stay so delicate because they are directly connected to our brains (that’s how the eyes send those light signals so fast).


Do the eyes heal quickly?

For small or simple injuries, the eyes do heal quickly. For example, a small scratch to the front of the eye can heal within a day. If the injury is more severe however then it could take weeks to heal. Many parts of the eye are made of nervous tissue and unfortunately, when nerve tissue is injured it might never fully heal.  


Why are some people blind?

There can be many reasons for blindness. Anything that blocks the light from entering the eye or makes the image blurry can lead to blindness. It can also occur if something prevents the light signal from reaching the brain or if our brain has difficulty processing the signals.

Some examples of blinding conditions include developmental or growing problems (genetics), scaring or cloudy changes in the cornea or the lens (cataract), and eye trauma. There are conditions in the back of the eye such as retinal detachments and glaucoma that damage the retina or optic nerve. Additionally, conditions such as stroke can also impact the vision by injury to the brain.

The most common cause of blindness in the world is cataracts. For adults in the US, the most common causes of blindness are macular degeneration, glaucoma, diabetes, and cataracts. For children, a common cause of blindness or poor vision is amblyopia.

Amblyopia is when the brain fails to learn how to see out of the eye which can happen if the eyes are not straight (misaligned), if the image is blurry (needing glasses) or if the eyelid is too low (droopy eyelid). With proper care from an ophthalmologist (eye doctor), amblyopia in a child can often be treated. If you notice your child has a “lazy eye,” please have them evaluated by an ophthalmologist while they are still young or the vision loss may become permanent. 


The eyes are such a fascinating and elegant part of us. Ultimately they are like a sophisticated camera, helping us observe and interact with the world around us. I hope you enjoyed learning the answers to these questions!

I’m Dr. Kane, and that’s my take on it.

At Tailored Eyes, we perform a thorough evaluation of your eyes and together formulate a customized treatment plan to meet your vision needs.

For more information or to book an appointment please call the office at 941-499-1570 or email us at info@tailoredeyes.com.

Steven Kane, MD, FAAO is a Cataract, Cornea, and Refractive Surgery specialist with Tailored Eyes in Sarasota county Florida. He proudly serves the people of Venice, South Venice, Sarasota, Plantation, Osprey, Nokomis, Laurel, Siesta Key, Casey Key, Bradenton, Lakewood Ranch, Anna Maria, Palmetto, Ellenton, St. Petersburg, Englewood, North Port, Punta Gorda, Port Charlotte, Charlotte Harbor, Manasota Key, Arcadia, Fort Myers and Cape Coral.