So get this; you just got lasik and are excited to see without glasses. To celebrate, you find your newest book purchase and sit down to read. After a short while, you start to notice an aching sensation and the feeling like the eyes are getting tired. You feel like you have to work harder to read the book. What gives?!
These symptoms you are experiencing are classic for eye strain. Lasik can't prevent you from getting eye strain. In fact, you are more likely to have some eye strain in the short term after lasik. This is from two main causes.
Dry eye
Everyone has some amount of dry eye after lasik. Typically the cornea senses dryness though tiny nerves that exist within the cornea. These nerves send signals to produce tears whenever there is an increase in dryness. But the lasik flap breaks the connection of these nerves. Until these nerves grow back, the cornea has a decreased ability to respond to drying out after lasik.
Dry eye can cause a wide variety of symptoms after lasik. More commonly people may have a burning sensation or the feeling like there is something in the eye. Sometimes people may also experience fluctuation of vision. But eye strain or the feeling like the eyes are tired and forced to work harder can be another symptom of dryness.
Take some to blink
When you sit down to read a book or work on the computer, you become "in the zone". You focus intently on all the words on the page or screen. You focus so intensely that you actually forget to blink. Blinking is essential for replenishing the tear film on the surface of the eye and protecting the cornea from drying out. Because you don't blink as frequently on a computer or while reading as you normally do, the eyes start to dry out. As you continue to work, this compounds on itself causing general symptoms of eye fatigue or eye strain.
Taking breaks while working on the computer or reading helps to rest the eyes and prevent fatigue. Sit back, close your eyes and rest. In addition to breaks, it's also a good idea to use preservative-free artificial tears a little more frequently while at the computer to prevent the eyes from drying out as much.
Are you drinking water?
In addition to the simple fact that you don't blink as much, when working hard you may tend to not drink as much water as you usually do. As the body gets dehydrated, the eyes follow - which exacerbates the dry eye. So keep a water bottle by your computer to sip on throughout the day. Heading to the water cooler is also a great excuse for a break!
The prescription of the eye
Whenever we look up close at an object, the lens inside of our eye changes to focus our eye up close. There is a muscle in our eye called the ciliary body that contracts when we look up close. By contracting, this muscles releases some tension on our natural lens causing it to plump up and change our focus. This process happens without us even realizing what we are doing. Our eyes are capable of seamlessly switching off between distance and up close.
How the eye focuses up close, image by MikeRun, CC BY-SA 4.0, via Wikimedia Commons
If the ciliary body is working too hard, however, you will start to get an aching sensation - eye strain. As an example, if you hold a sheet of paper one inch from your eyes and try to read it, you will cause this ciliary body to work hard and cause that ache (if you aren't naturally nearsighted). The longer you read or work up close, the more this muscle tires and the more eye strain you get; again, another reason to take some breaks.
If you are nearsighted, this ciliary body doesn't have to do as much work when you go without your glasses or contact lenses. Your vision is already focused up close.
On the other end of the spectrum, this ciliary body has to do lots of work for people that are farsighted. Not only does the ciliary body and lens have to focus up close, it also has to focus through uncorrected farsighted prescription. People who are farsighted and can see well enough in the distance without glasses may notice excess eye strain.
Changing the prescription with lasik
So we take all these people, the nearsighted folk and the farsighted individuals and we give them lasik:
- The nearsighted people can notice some extra eye strain. This is especially true if they were used to taking off their glasses to read up close. Because they are no longer nearsighted, they have to use their ciliary muscle to focus their lens to read up close. They will experience a little more eye strain as a result.
- The farsighted individuals, on the other hand, can actually notice improvement in their eye strain. Because they no longer have to focus through their farsighted prescription to see, their ciliary muscle will no longer be overworked.
There is a third category of prescription: Gradually over time, the lens has a harder time focusing up close. This is a natural process called presbyopia and happens to everyone typically in the mid to late forties. The ciliary body may have to work harder for minimal gains and eye strain can result.
- Lasik can't reverse presbyopia. After lasik with vision corrected for the distance, those individuals will still have difficulty and strain when trying to read up close. Again for the nearsighted individuals who may be used to taking their glasses off to read, they may notice the eye strain and difficulty reading up close a lot more than what they are used to. One way to get around this is to correct vision for both up close and for distance. This is known as mini-monovision and works quite well to improve the up close vision, get out of reading glasses and reduce eye strain.
Getting on target after lasik
As quick as lasik works, it actually isn't fully instantaneous. While everyone notices blurring from a fog or haze during the first 24 hours after lasik there is another more subtle effect that not everyone notices.
For the first few days after lasik, the prescription more than likely isn't completely on target. During the lasik procedure, sterile water is used to float the lasik flap back into position and clean the space underneath the lasik flap. The lasik flap absorbs some of this sterile water and gets a little bit of swelling. This swelling eventually goes away but can actually changes the prescription of the eye. This causes a temporary overcorrection in the lasik prescription.
Most people don't notice it because most people have a nearsighted treatment. When a nearsighted treatment goes beyond the target, you end up slightly farsighted. Your ciliary body muscle is able to focus through this small extra prescription. However, some people may notice this as additional eye strain early on after lasik when reading up close. Their ciliary body is becoming slightly more overworked than normal. This is especially the case for those nearsighted individuals who are used to taking their glasses off to read (since their ciliary body never really got much work).
Gradually this swelling resolves and the prescription resolves back on target. But this same concept applies for those that may not have ended up completely on target after lasik. If you have a persistent overcorrection of your nearsighted prescription you may notice more challenges and eye strain when reading up close despite still having good distance vision. This will especially be noticeable for those which are suffering from presbyopia.
Summary
Eye strain can be annoying when you are trying to get work done and you may notice more eye strain after lasik. But fortunately, as the eye continues to heal, the eye strain returns to pre-lasik levels. But it's still a good idea to give your eyes a break.
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