Our eyes are hands down the most complex and impressive organs in our bodies. What makes them so impressive is not only the fact that they let us perceive a wonderful three-dimensional world, but how they do it. Eyes are an incredibly intricate organ unlike any other. Our eyes allow us to see in color, to see near and far, and to have a sharp sense of perception.
The eye would not be able to do any of this without the help of our brains. They work together to give us this magnificent sense of sight. How do they work exactly? Well it’s a lot more complicated than simply looking and seeing.
Your eyes are like a blockbuster movie; what we see in a movie is just the end product of months and sometimes years of work, with thousands of crew members. What we see with our eyes is just the end product, the magic really happens behind the scenes.
How Do Human Eyes Work?
The very basic explanation to how our eyes work is that light bouncing off objects is translated through our eyes and brain to make comprehensible images. If this sounds familiar to you it’s probably because our eyes work just as cameras do – or rather, cameras act as our eyes do.
In terms of sight, our eyes are responsible for keeping a clear and focused image of the outside world. Our brain works to recognize these images using visual memory. Before we get into technical terms, have a quick look at this human eye diagram. If you’re a visual person (pun intended), diagrams are a helpful way to understand how everything works.
The first step to creating images with the eye starts at the cornea. Light bouncing off objects is sent through the cornea, where it will then refract and bend light through the pupil, the black center of our eyes.
If you’ve ever paid close attention to your pupil, you’ll have noticed it expanding and contracting. This is the doing of the iris, or the colored portion of your eye. The iris’s job is to calibrate the amount of light being let in. For example, in darker settings, your iris will expand to let as much light in as possible.
The light will then travel through the lens, a flexible part of the eye that will once again bend the rays of light to further focus before sending them off to the retina at the back of the eye.
Your eyes (or the camera), has captured the scene, now it’s time for the editing. The editing of visual images happens at the back of the eye, starting with the retina. The retina is a thin tissue packed with cells called photoreceptors. There are two types of photoreceptors: rods and cones. Rods are in charge of detecting light and dark lighting as well as motion, and cones are color sensitive receptors.
These photoreceptors are most concentrated in the area called the fovea. This area is also known as our central vision. Because of the high concentration of photoreceptors in this area, it is where our vision is sharpest. Images which fall further away from the fovea are sometimes blurry and not as sharp but can still be seen. This is known as peripheral vision.
Once these rods and cones receive the images, they are converted into electrical impulses. These impulses are then sent through the optic nerve, and to the brain.
How the Brain Works with the Eyes
Through the optic nerve and through the cerebral cortex, at the stem of the brain, the electrical impulses have officially left the eye. Now they’re on their way to two different regions of the brain: one being to a group of cells called the pretectum; and the second being to a nucleus called the superior colliculus.
Both these regions of the brain interpret the impulses in different ways to form an image. The pretectum controls pupillary size in response to light that we were talking about before. The superior colliculus helps move our eye in short jumps called saccades, allowing us to perceive motion, but also to stabilize motion. Our eyes are always moving therefore without the saccades, everything we see would be blurry.
Projections from the retina also travel to the lateral geniculate nucleus, which is found deep inside the brain. Here, the projections are divided into streams; one with color and structure, and the other with contrast and motion.
The layers of these streams are then sent to the final stage of production: the primary visual cortex, otherwise known as V1. Or for our purposes, the final theatrical cut of our movie.
V1 is the area that allows us to perceive a three-dimensional world. Through the positioning of cells and visual information received by V1, we can perceive images horizontally, vertically and depth, thus giving us the three-dimensional viewing we’re accustomed to.
As an added bonus, our brain will sometimes rely on visual memory to discard images that may not be necessary. This is called eidetic memory (different from photographic memory). Focus on a nearby object, then close your eyes. You will likely see that object for a second or two before it disappears. Your brain makes the quick decision what to remember and what to discard.
Our brain is our visual organizer. Without it, the images transferred to us by our eyes would just be senseless light and information from our eyes that we wouldn’t be able to recognize or process. The same goes the other way, without our eyes our brains would have nothing to interpret.
The wonder that is the three-dimensional visual world around us would be inconceivable without our eyes and brain working in tandem. Who knew simply opening your eyes was such a complex task? Just like a movie, you may not always be aware of the behind the scenes, but it’s what makes the end result perfect.