Sight is one of our most complex senses. But have you ever stopped to wonder just how eyes work?
The process of human vision is pretty amazing.
To better understand how we see things, let’s first cover what our eye components, or “structures” do, and help answer the question of how does the eye allow us to see? Let's take a minute to find out more about this.
Parts of the eye—the exterior
Our eyes are organs, just like our heart, kidneys, and our skin (our largest organ). Eye anatomy is incredibly complex. Each eye has over two million working parts. These include external structures like:
- Your eyelids, which offer protection for your eyes.
- The sclera and cornea, which cover and help protect the eye’s interior.
- The tear film, which carries oxygen to the cornea and helps keep your eyes healthy and comfortable.
Fun facts: Did you know that eye blinking happens about 12,000 times for each of us as we go about our day, and that the cornea is the only structure in our body that doesn’t have blood vessels? Our blood delivers oxygen to our body parts, but the cornea gets it directly from the air. Why? Transparency. It’s necessary for clear vision.
Now that we understand what’s on the outside of our eyes, let’s take a look at what’s located inside and answer our question of how do we see an object like the rising sun or our favourite breakfast plate in the morning.
The eye interior
The main interior structures of your eyes include:
- The iris, which is the coloured part of your eye.
- The pupil, the black circular opening in the centre of the iris that lets in light.
- The crystalline lens, suspended behind the iris, which allows you to focus on near and far objects.
- The retina, which is a very thin layer of millions of photoreceptors called "rods and cones."
As you greet each day, light enters the eye through your cornea and your pupils. If you’re in a dark room and turn on bright lights, your pupils constrict to reduce the amount of light. The opposite happens if you walk from bright sunshine into a darkened room. Your pupils dilate to allow more light in so you can see better in your new surroundings.
After the light passes through your pupils and crystalline lens, it focuses on the retina. And here’s the surprising part, the images flip upside down on the back of your eye! Yes, you read that correctly.
As light reaches the back of your eye, it travels along nerves in your retina that come together as a bundle. These images then travel all the way to the brain via your optic nerves. As your brain processes this information, it flips the images again so we don’t see the world upside down. Without this occurring, we could be living some incredibly awkward lives!
Our vision system is efficiently designed indeed.
While this aspect may sound a bit strange, it’s the way our body can best process the information quickly. This begs the question, what happens when everything doesn’t work perfectly with your eyes?
Common eyesight problems
As we’ve read, the anatomy of the eye is fascinating. You see clearly when your cornea, crystalline lens, and retina are all working together properly. Unfortunately, this isn’t always the case.
Having less than perfect vision is often the result of genetics. If your parents wore corrective lenses at a young age, then it’s likely you’ll need them early on in your life as well. Here are some common vision problems we face.
When the light entering your eyes focuses in front of the retina, rather than directly on it, you experience myopia or nearsightedness. Objects at a distance will be blurry and unclear. If you have myopia, it may be that your eyes are larger than normal. (Read more about nearsightedness.)
Likewise, as you may guess, the opposite applies to farsightedness or hyperopia. In this case, the light entering your pupils focuses behind the retina. This is often the result of having a flatter cornea or shorter eye than normal. (Read more about farsightedness.)
Another vision problem that everyone faces at some point is presbyopia, which occurs when the crystalline lens loses its ability to focus properly. Objects up close then appear blurry, which is why you often need to hold a restaurant menu farther from your face to read it once you reach your mid-forties. (Find out much more about presbyopia.)
As we’ve learned, it takes many parts of the eye for our sight to work correctly. But when things go wrong, we’ve advanced technology to help correct vision problems.
Next time you wake up in the morning, consider taking a moment to marvel at how your eyes are working to show you the new day.