Sometimes after finishing a long day at work you just want to sit back and relax with your favorite novel. But how come you notice when you go to read, things are just a little more blurry. Did your astigmatism get worse because you are tired? Actually, there is a situation in which this can happen.
Prolonged reading can actually cause you to temporarily develop more astigmatism (and also tire you out). But just being tired itself won’t cause your astigmatism to increase. Your vision can also be more blurry from other causes when you are tired such as dry eye and eye strain.
Regardless of the cause, perhaps you just need to take a break. But let’s explore a little more about what may be causing your vision to be blurry.
What Actually Changes Astigmatism?
The vast majority of astigmatism in your vision comes from your cornea. A normal cornea is shaped more like a dome or basketball. If your cornea has astigmatism, it takes more of a shape like a football. One direction of the cornea (such as up and down) is steeper than the other direction. Light that enters the flat part of the cornea focuses at a different spot than light that enters the steep part of the cornea. This causes vision to be blurry.
As long as the cornea isn’t changing shape, astigmatism remains quite constant. Becoming tired in and of itself doesn’t cause any changes in your cornea.
But there ARE actually things which can cause temporary changes in your astigmatism. And in fact, reading is one of those things.
Looking down to read; image by by Seven Shooter on Unsplash / cropped from original
When you look down to read, your eyelid drops down and rests more on the cornea. The force of the eyelid can actually press into the eye and cause small changes. This can actually cause more astigmatism!
So, if you are tired from reading for an extended period of time, you can actually have more astigmatism. But the actual being tired part isn’t what caused the astigmatism.
To be fair, we aren’t talking about massive changes in astigmatism. And not everyone is going to have the exact same changes. Some people will have more than others. But with prolonged reading, your eyelids can cause changes to your cornea which can blur your vision.
Other Reasons For Blurry Vision When Tired
Astigmatism isn’t the only cause of blurred vision. Plus, astigmatism can’t explain why your vision can be blurry when you’ve been looking straight ahead (not down) at a computer for a while. Astigmatism also can’t explain why your vision is blurry when you are tired simply because you didn’t sleep well. There are other reasons.
Dry Eye
When we spend time in front of a book or a computer, we don’t blink as frequently. In fact, any task which involves a large amount of our attention will cause less blinking. Each blink of the eyelid is important to restore a smooth tear film on the surface of our eye.
The tear film is the protective coating of the eye to keep the surface healthy. A smooth and regular tear film is essential for the overall health of the surface of the eye. It is also critical to provide good vision.
All light that enters our eye has to first pass through the tear film. When this tear film is smooth, light passes through without any issue. But if this tear film dries up and evaporates away, the tear film can become irregular.
If the tear film evaporates too quickly, the eye drys out. The surface of the cornea starts to become “sick" and can become a little cloudy. This can cause blurry vision.
If you can imagine, if you spend long hours working on tasks where you don’t blink as much, such as working on a computer, you can notice things start to become more blurry. Your vision isn’t blurry from astigmatism, it is blurry from extra dry eye cause by those tasks.
But much of the blurry vision from dry eye instead comes from trying to look out of an irregular tear film. An irregular tear film scatters light that enters our eyes and makes things blurry. But immediately after blinking, after the eyelid provides a fresh coat to the tear film, the vision gets better. Seconds later, the vision becomes blurry again because the eye drys out. This leads to fluctuation of vision.
But dry eye can also be cause by a poor night’s sleep. At night, when our eyelids are closed, there is a lot of healing which happens on the eye. Having good rest is critical to prevent the eyes from drying out. If you “burn the midnight oil" and stay up later than you should, your eyes don’t get as much rest as they need. As a result, the eyes can be more dry and you can experience more blurry vision.
Prolonged Focusing Up Close
When you are tired, you may have also noticed another issue going on. You may have had trouble focusing. This can especially be the case if you have recently spent a lot of time on up close work such as reading.
Until we hit our mid-forties, our eye is capable of changing it’s focus. When we want to look far away, the eye relaxes the focus to see in the distance. When we want to read a book or look at our phone, our eye tightens the focus to see up close. This action is controlled by a special muscle in the eye called the ciliary body. This muscle works on the natural lens inside our eye to change it’s shape and change where it focuses light.
How the eye focuses up close; image by MikeRun, CC BY-SA 4.0, via Wikimedia Commons
But as with any muscle in our body, this ciliary body muscle can become overworked - with prolonged sessions of looking up close.
When this muscle becomes overworked, you can develop achiness and eye strain. And sometimes if you are tired, you may even just unconsciously decide to give this muscle a break. This muscles relaxes, the lens changes focus and you have a harder time maintaining your ability to focus and see up close. A sign you’ve been working too hard!
So take breaks once every hour. Look out a window or off in the distance to prevent your eyes from becoming overworked.
Summary
There are reasons why your blurry vision can become more blurry when you are tired. Astigmatism does contribute a small portion. But dry eye and eye fatigue also will cause you to have blurry vision when you are tired.
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