Your eyes probably become itchy because extra-reactive harmful oxygen molecules damage the corneal cells and long-term sleep deprivation leads to corneal cell death. Sleep deprivation also damages the tear film, which protects our eyes from damage.
Sleep is essential for all animals in order to maintain their physical and mental health. Unfortunately, sleep deprivation is a common issue for many people these days. Whether it’s due to hectic work routines, late-night gaming sessions, or a crying baby, everyone has reasons for being nocturnal animals.
During a sleep-deprived bout, you may have noticed that your eyes become very irritable and itchy. When I was writing my Master’s thesis, I stayed up for many nights, and my eyes were often sore from all the rubbing and scratching.
However, it’s not exactly the eyes that become itchy… it’s the cornea that troubles us.
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What is the cornea?
The cornea is the eye’s clear front surface. It’s like a protective eye coat that defends the eye from infections, dirt, and water, while also focusing light rays on the retina for our vision.
The cornea is a protein-containing tissue made up of different types of cells of about 5-7 layers, called the corneal epithelium. This multi-layered tissue has different cell types, with one of the main ones being corneal epithelial cells.
Surrounding the cornea’s surface is a smooth protective layer called a tear film. It is the first layer that light shines on when it strikes the cornea. It protects the eyes by providing moisture, so they don’t feel dry. It is also an oxygen source for the eye cells and other biological protective molecules.
Our body maintains its vital corneas very delicately. The corneal cells are maintained by a pool of stem cells called corneal epithelial stem cells. These cells can grow and develop into corneal epithelial cells to replace dead or old ones. This cycle of replacing old corneal cells with new ones is called homeostasis.
If you were to take a football in the face and hurt your eye, your corneal stem cells would develop into adult corneal cells quicker to replace the damaged ones. This entire procedure goes on throughout our lives.
However, sleep deprivation disrupts this balance, which is where the eye itchiness starts.
Why does the eye get itchy?
The cornea is exposed to solar UV light and oxygen most of the time. The corneal cells break down this oxygen metabolically to release Reactive Oxygen Species (ROS). UV light increases the ROS generation rate. These are highly reactive and unstable oxygen-containing molecules that damage cellular proteins, lipids and DNA. That ultimately leads one thing – cell death.
Plenty of research shows that sleep deprivation increases ROS generation in the body. Interestingly enough, a study found that sleep-deprived people shed tears with greater ROS levels. This indicates that sleep deprivation also increased ROS levels in the eyes.
A study published in April 2022 performed on mice pushed us closer to answering why exactly our eyes become itchy. According to the study, these extra-reactive harmful oxygen molecules damage the corneal cells, while long-term sleep deprivation leads to corneal cell death.
That’s not all! Sleep deprivation disrupts the corneal cell cycle balance, i.e., homeostasis. Sleep deprivation makes the corneal stem cells divide and develop rapidly, depleting the pool sooner. The reactive oxygen molecules kill the developed cells quickly and the corneal epithelial stem cells grow faster than they should.
The corneal epithelial cells’ gene expressions are also disrupted. The study found that over 300 genes were not expressed as they usually should be. Such genetic changes could explain why the corneal epithelial stem cells divide so rapidly.
Additionally, the reactive oxygen species damage the tear film—our cornea’s safety shield.
These biological effects make our cornea irritable and uncomfortable, leading us to constantly rub our eyes.
Don’t worry! Our body has a great way of looking after itself.
How does our body cope with cornea damage?
Sleep deprivation is something that troubles people all over the world, but not everyone’s eyes are equally damaged. That’s because our body has many self-defending molecules to protect our eyes from such damage.
Remember the tear film, our mighty eye shield? Apart from providing moisture and lubrication, it also contains anti-oxidant molecules like vitamin C (ascorbic acid) and cysteine that protect the cornea from ROS damage. It also secretes antioxidant enzymes that break down the ROS molecules.
However, these defenses don’t last forever. Eventually, sleep deprivation catches up with us and the damage caused is not repairable by the body. The tear film damage worsens with a continuous lack of sleep. This weakens the tear film’s protective capabilities (its antioxidant capacity). At this point, the oxidative stress burden exceeds what the eye’s antioxidant mechanism can handle, resulting in oxidative damage.
The best thing would be to ensure you get consistent, good-quality sleep.
I understand that it’s not possible for some people to always sleep regularly. In that case, It would be better to seek help of some kind. Consult your eye doctor and maybe get some eye drops that can ease your discomfort. However, high-quality sleep is the best thing you can do to maintain good health—of your eyes and every other part of your body!
Further research will focus on developing antioxidant eye drops or drugs that can help undo the genetic disturbance in the eyes, which could help fight eye discomfort in sleep-deprived people.
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