The Root of Dry Eye Syndrome
Updated: Sep 16, 2020
Why do your eyes feel irritated after staring at a screen?
Do you remember being a kid and having a staring contest with your friend or a sibling? Sounds simple: just look at the other person and don't blink, right? How hard could that be?
And yet everyone eventually gets to a point where they have to blink their eyes. But why is that? If we can consciously, intentionally control the muscles of our eyelids, why can't we simply force them to stay open until we win any staring contest?
The answer for this can be traced back to mankind's evolutionary roots. At this point, you may be wondering, "What does a caveman have to do with Computer Vision Syndrome?", but this topic is really the first step to understanding Dry Eye Syndrome (DES), a disease that affects millions of people all over the globe.
Let me explain: our eyes are critical sense organs that are necessary for survival. In the modern world, society has evolved to better accommodate people who are blind or who have poor vision, but that was not always the case. Any animal in the jungle that can't see and detect predators or catch prey is less likely to survive. And in the survival of the fittest, fitness is measured in part by one's visual capability.
The Eye's Defense Systems
Thinking in these terms, it makes sense that the human body has evolved to protect our eyes. Look in the mirror at yourself and think about how the anatomy of the eye plays a defensive role. Here are just a few ways:
1) Eyelashes - Besides making us look pretty, these hair follicles on the upper and lower eyelids act as a barrier to prevent dust and microscopic particles from falling and landing directly onto the eye, thereby preventing infection. Could it be that long eyelashes are considered a desirable physical trait because it's baked into our wiring that a potential mate with long lashes is more likely to survive? Probably not, but it's an interesting theory.
2) Eyelids - This is probably the most obvious eye defense system. These small folds of skin are fairly thin, but they really do a lot to protect the eye from physical damage. For a quick demonstration, close your eyes shut and press onto your eyeball with your finger. No big deal, right? Now, for comparison, keep your eyelids open and press directly against your eye with the same amount of force as before. (Don't actually do this.) If the very idea of touching your eyeball makes you squeamish, then that's proof enough of the role the eyelids play in defense.
3) Corneal Nerves - Okay, so this one you can't actually see just by looking in the mirror. But the truth is that the cornea is just about the most sensitive tissue in the entire body. It has more nerve endings--clinically, we would say that it is more "densely innervated"--than, say, the heel of your foot, or the tip of your nose. This extreme sensitivity to any pain or physical contact is itself a defense mechanism for the eye, and I'll explain why.
Okay, But First: What is the Cornea?
The cornea is the clear tissue at the very front of the eye. Looking at yourself head-on in the mirror, you can't really "see" the cornea because it's clear. The colored part of the eye--the iris--is behind the cornea, so you're looking through the cornea to see what color somebody's eyes are. For a better view of the cornea, look at someone else's eye from the side. Note the curved shape and how their eyelids glide directly over it every time they blink.
The nerve endings of the cornea are packed densely within that thin clear corneal tissue. Even with a microscope the nerve endings are not readily visible, so you definitely won't see them just by looking in the mirror. But these nerve endings are critical for the health of your eyes.
Why the Corneal Nerve Endings Matter
From an evolutionary standpoint, it makes sense that the cornea--with so many nerve endings--is extremely sensitive to pain or any physical contact. Our brain needs a strong and clear signal that something is threatening this critical sense organ necessary for survival, so it must take action to mitigate that risk. That action might be closing the eyelids or turning the head away.
Furthermore, as mankind has developed to know the pain of something touching our eyes, we have evolved with reflexes to prevent things from even hitting our eye in the first place. That's why an infant will flinch as something comes close to its face. We instinctively shut our eyelids if we detect an object approaching our eyes, whether that's a tiny ladybug or a softball at high speed. Imagine prehistoric man running through the forest chasing his prey, dodging tree branches so that they don't hit his face and eyes. These protective instincts trace back to the highly sensitive cornea, which evolution has told us we must protect for our very survival.
The Cornea and Dry Eye
And this concept brings us back to the modern Digital Age. Every day, hundreds of millions--if not billions--of people use a computer or other screen at some point to survive. They don't chase down their dinner in the jungle, but they work at a computer for their job to earn a paycheck to feed themselves and their families. The woman above staring at her laptop is the result of eons of evolution, complete with two croissants, cup of coffee, and O. J.
But what she probably doesn't know is that, in this present-day work setting, she still needs to take care of her eyes. They are still critical to her survival. And they are still at risk. In the next post we'll explain how, and also why you should never challenge your computer screen to a staring contest.