Squinting causes two reactions that help you visualize the world around you in better detail. First, it changes the shape of our eye, allowing light to be focused better. Secondly, it decreases the amount of light that is allowed to enter the eye. Light coming from a limited number of directions allows that light to be more easily focused.
If all that seems a bit vague, it is. To completely understand why these two reactions help us see better, let’s take a more in depth look at vision, light, and how the eye works.
At its core, vision is just the perception of light by our brains. It’s important to note, the term “light” can refer to any electromagnetic radiation, not just the radiation in the visible spectrum. This radiation is a natural result of one of our four fundamental forces, electromagnetism.
Electromagnetic radiation can be classified into seven types- Gamma, X-ray, Ultraviolet, Visible, Infrared, Microwave and Radio wave. Visible light actually comprises a very narrow range of frequencies that can be perceived by humans. This human-visible light has the same characteristics of all types of electromagnetic radiation. Namely, it comes in the form of frequencies. It’s these specific frequencies (wavelengths) that give our eyes the ability to perceive colors, as well as objects. Other frequencies allow us to see our bones through our skin, via X-rays (but that’s another topic altogether).
How does this wonder of evolution, the eye, actually work?
Our eyes have many different layers functioning together to trap light and turn it into an electrical impulse the brain can process. The outermost layer is called the sclera. This is the white part of the eye that gives it its shape, and where the muscles that control eye movement attach themselves. On the front part of the sclera is a transparent bit called the cornea. All light entering the eye must first go through the cornea.
The next layer is called the choroid. This layer contains the numerous blood vessels that supply the many parts of the eye with nutrients. It also contains the iris (the colored portion of the eye) and ciliary muscles that control the lens of the eye. Together with the cornea, the lens helps refract all of the light that enters the eye and focus it on the innermost layer, the retina.
The retina contains two different types of photoreceptors responsible for vision: rods and cones. When light strikes these cells, it reacts with visual pigments within them. These pigments contain a class of proteins called opsins. Together, with a molecule known as a chromophore (in humans this chormophore comes from vitamin A), light frequencies reacting with these pigments cause the electrical impulses your brain receives.
In the human eye, there are four main types of opsins that react to different light wavelengths. Cones use three types and Rods use one.
Rods far outnumber Cones in the human eye, approximately 120 million compared to just 6-7 million cones. They are much more sensitive to light than cones, and as such are the cells mostly responsible for night vision. They are also better at sensing motion with the highest densities of them outside the central part of the retina known as the macula. This is why they are mostly responsible for your peripheral vision. Rods using only one type of protein, rhodopsin, to create an impulse leaves them the inability to distinguish color.
Cones, while less in number and sensitivity than rods, are responsible for color and high resolution. Cones use three types of opsins that react to short, medium, and long wavelengths of light. Those frequencies correspond roughly to the wavelengths responsible for blues, greens, and reds. Because of this, they are referred to as blue, green and red cones. For us to see color, two kinds of cones must be triggered by their respective wavelengths of light. The color we perceive is based on the level of stimulation each of those cones received. So if an equal number of red and green cones are stimulated equally, we might see shades of yellow/orange.
Now that we know how the eye changes light waves into electrical impulses, let’s look more deeply at why squinting helps you see better.
As we now know, cones are responsible for high resolution and color. The highest density of cone cells reside in an area of the retina called the macula. In the center of the macula is an area known as the fovea centralis. The fovea only contain cones that are tightly packed together. No rods are present here. This highly dense area of cones gives us our greatest image resolution. As we focus our vision on something specific, like the words you’re reading now, the eye continually moves so it refracts the light coming from those words, directly on the fovea, leaving you with a detailed image.
When the eye is completely open, light waves from a wide range of directions are entering it. All of those waves are processed by all of the rods and cones in the different areas of your eye. By squinting, you are reducing the amount of light, and the number of incoming angles, that needs to be focused, making it easier to do so. It’s like trying to hear a specific person in a room filled with people talking. The unwanted noise drowns out the noise you actually want to focus on making it more difficult.
The shape of your eye’s lens and its ability to change shape, allows us to focus the light entering the eye, on the fovea. Should you be born with an abnormally shaped lens or eyeball, or your lens loses its elasticity (as can happen with age), its ability to focus light on the fovea is reduced. By squinting, we change the shape of our eye, ever-so-slightly. This helps the lens focus the light appropriately on the fovea.
In the end, if you forget all the medical terminology or finer details, in a nutshell, you’re changing the shape of your eye to better focus the light where it needs to go, while also decreasing the total light let in, more or less helping you filter out the “noise”.
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- The frequency of electromagnetic radiation that can be seen in the visible spectrum ranges from around 400 nanometers (nm) to approx. 780nm. The wavelengths for specific colors are as follows:
- Violet- 400-420nm
- Indigo- 420-440nm
- Blue- 440-490nm
- Green- 490-570nm
- Yellow- 570-585nm
- Orange- 585-620nm
- Red- 620-780nm
- As stated in the article, there are red, blue, and green cones. Meaning those cells respond better to the specific frequencies of light that correspond to those colors. Specifically, blue cones are most sensitive at frequencies of 445 nanometers, green cones 535 nanometers, and red cones at 575 nanometers. Around 64% of our cones are red, 32% green, and only 2% are blue.
- Ever wonder why ship and airplane captains use red light to see at night? As stated before, rods are what we primarily use to see at night. They’re also very slow to respond to changes in light intensity. If you don’t believe me, try walking into a dark room after being in the sunlight and see how long it takes for you to see again. It’s with this in mind that red light makes sense. Rods don’t respond to light wavelengths in the red spectrum. This leaves no need for the adjustment period required by white light, giving them the ability to look down, read a map, and then stare out into the darkness with confidence.
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