It can be very disappointing to go through the whole process and expense of lasik only to end up with blurry vision on the other side. But blurry vision after lasik does happen from time to time. There are some very common causes and there are some which are much more rare.
The most common cause of blurry vision after lasik is having some residual prescription error. But dry eye and weakness of the natural lens are also common causes. Finally, there are rare causes such as trouble with the lasik flap, increased aberrations or infection.
Fortunately, there are ways to treat and improve many of these causes of blurred vision (and especially the most common ones). Sometimes it just takes patience, other times it may take an additional step or procedure to resolve.
Residual Prescription Error
This is the most common cause of blurred vision after lasik. Simply lasik didn’t treat all of your prescription. Lasik is highly accurate (more than 99.5% of people will get vision without glasses of 20/40 or better), but it isn’t perfect. If we narrow down to 20/20 vision instead, than only around 91% will achieve this result without any glasses or contact lenses after lasik. Still high, but not 100%.
There is a considerable difference between 20/40 and 20/20. While you can still see at 20/40, it just won’t be as clear or as sharp as your vision at 20/20 (see also What Does 20/20 Vision Mean?).
What Causes This?
There are a variety of reasons why you can end up with residual prescription remaining after lasik. While the treatments from lasik are very accurate, we are still dealing with some variability.
The biggest cause is that the prescription just wasn’t fully treated.
To help optimize the treatments, surgeons develop nomograms. These computer nomograms take a prescription and guide the surgeon on what should be programed into the laser to achieve perfect results. These patient results are then fed back into a massive database. These results are then used to further optimize the nomograms and continue to make things as accurate as possible. These nomograms help to eliminate any variability in results from the laser (is it a “hot" laser that treats more than expected or a “cold" laser which does the opposite).
This is especially a cause when treating large prescriptions and especially large amounts of astigmatism. It is much harder to hit the target perfectly with large prescriptions (similar to when playing golf, trying to sink a long putt - much harder).
The second main cause is that you were originally on target but developed some regression.
Regression can occur through a variety of reasons (although the exact causes of regression are incompletely understood). Lasik changes the shape of the cornea. And lasik expects the cornea to retain that same shape as when the laser finishes its treatment. But sometimes what we want things to do isn't what happens. The altered cornea can have a different tension which slightly changes how steep the cornea becomes. The epithelium on the surface of the eye can start to thicken in areas and change the shape of the cornea. As the prescription is based upon the shape of the cornea, these changes can cause regression of prescription after lasik.
Also check out Why Does Lasik Wear Off For Some
Finally, the eye prescription may just not have been fully stable before lasik.
The prescription of our eyes tends to stabilize once we’ve gone through puberty. Thus it is recommended to wait until the ages of 18-21 before getting lasik done. In addition, it is important to make sure that even beyond this age that the prescription isn’t changing. Rarely this can happen to those who do additional study in fields that require intense book work (think lawyers, doctors and engineers). If the eye isn’t done changing, lasik won’t stop that change and some prescription can return after lasik because of that reason.
What Can Be Done About Residual Prescription?
Fortunately, there are ways to correct residual prescription after lasik. It is called a lasik enhancement.
Once your prescription is deemed to be stable (which for most people occurs about 3 months after a nearsighted lasik treatment or 6 months after a farsighted lasik treatment), the surgeon will typically lift the lasik flap back up and do an additional treatment with the lasik laser. This is typically called a lift-flap enhancement (given that the surgeon is lifting up the lasik flap).
Its a relatively straightforward procedure with a recovery very similar to what you experienced after your original lasik procedure.
Getting your prescription back on target after a lift-flap procedure has a high chance of success. If we return to the golf putting analogy, we are trying to sink a tap-in rather than a 100 ft putt. An enhancement is a much smaller prescription; less change in the cornea and thus less that variability can affect.
Dry Eye After Lasik
Dry eye is common after lasik in the first few months. Everyone after lasik will experience some degree of dry eye. The lasik flap and treatment disrupt tiny little nerves within the cornea. These nerves are involved in allowing our eyes to produce tears. Thus, after lasik, the eyes have a much harder time producing tears - until these nerves regrow.
Most people associate dry eye with burning or scratchiness or general eye irritation. And yes, dry eye causes all those things, but dry eye can also cause blurred vision.
When light passes into our eye, before it even reaches the cornea (where the lasik treatment is performed), it has to pass through the tear film first. In normal healthy eyes, this tear film is nice and regular and conforms to the shape of the cornea.
But in dry eyes, this tear film can become irregular. When light hits this irregular tear film, it starts to scatter - this causes blurred vision.
Typically the symptoms that people experience when dry eye is causing their blurred vision is they notice fluctuation of vision. Immediately after blinking, the eyelids work like squeegees to smooth out the tear film on the eye. But since this tear film is inadequate, it drys out quickly after blinking and becomes irregular. Vision is sharper right after blinking but starts to become blurred a few seconds later
This blurred and fluctuating vision can be noticed more during tasks in which you are concentrating more. Think reading, driving or working on the computer. During these tasks, you don’t blink as frequently and you can notice the eye drying out more.
Using preservative free artificial tears is often the first step to treating dry eye after lasik. But these tears can also help you figure out if this is the cause of your blurred vision (or one of the causes). If you put an artificial tear drop in your eyes, this tear replenishes the tear film on the surface of your eye. It makes it much more robust to drying out. You can actually notice improvement in your vision and less fluctuation after putting a tear drop in your eye. At least for a few minutes.
Preservative Free Artificial Tears; Image courtesy of Amazon.com note: As an Amazon Associate I earn from qualifying purchases
Natural Loss of Up Close Vision (Presbyopia)
Everyone at some point in their life will require reading glasses, bifocals, progressive glasses or just simply need to take off their glasses to see things up close. This is something called presbyopia and happens starting in our 40s.
This loss of up close vision occurs due to the natural lens inside our eye no longer being able to focus. As this lens loses its focusing ability, things start to become more blurred up close.
Lasik can’t reverse presbyopia. After lasik, the lens inside your eye will still have the same trouble focusing.
But lasik does change the prescription of the eye - and this can change how presbyopia affects your vision.
This is especially important for those who are nearsighted before lasik. Nearsighted individuals don’t have any issues seeing up close without any glasses (as long as your nearsighted prescription isn’t too high). Notice in the first paragraph, I mentioned “need to take off glasses to see things up close". This is the exact situation that applies to nearsighted individuals.
Nearsighted individuals who are starting to lose their up close vision may find that they can’t see as well up close in their glasses and so they take off their glasses (or look underneath them) in order to see things up close.
So if these nearsighted individuals are corrected for distance with lasik, they will suddenly notice their up close vision is blurry. They experience the full effect of their presbyopia because they no longer have that superpower of taking off their glasses to read. Instead of requiring glasses for distance, they now require glasses for up close instead. While this can be great for some, this can be annoying for others (especially if they aren’t educated well enough ahead of time).
There is a technique, however, to provide both distance and up close vision after lasik. This is through something called mini-monovision or monovision. One eye is corrected for the distance while one eye is corrected for up close vision. Thus, between both eyes, the full range of vision is covered. While this takes some adjusting to, it is a very popular way to correct vision for those with presbyopia to keep out of reading glasses.
Blurred Night Time Vision (from aberrations)
It’s worth noting that lasik can potentially create extra scattering of light that can’t be corrected with glasses or contact lenses. These are known as “higher order aberrations" and most frequently manifest as having additional trouble with night time vision but can also cause additional blurred vision if severe.
Note: If you have residual prescription (see the most common cause up above), you will more than likely have blurred night time vision; but this is correctable with glasses.
Lasik corrects vision by changing the shape of the cornea. For nearsighted individuals, the cornea is made more flat and for farsighted individuals, the cornea is made more steep.
But lasik doesn’t change the entire cornea. Lasik only corrects the center portion of the cornea. This leaves the very edge of the cornea untreated.
Because of the difference between these two parts, light that passes through the treated part focuses at a different spot than light that passes through the untreated part. This mismatch where light focuses creates aberration (especially the type spherical aberration). Because light is focusing at two different locations (from the treated part of the cornea and from the untreated part), a halo or starburst can form around lights.
And as light isn’t perfectly focused in your eye, these aberrations can also create some blurred vision.
But fortunately, lasik treatments have evolved over the years to largely eliminate these aberrations. In fact, bothersome symptoms of halos or starbursts are more likely to be less AFTER lasik than before. And any symptoms that do occur generally improve over time.
Serious Causes
We’ve gotten pretty far before even mentioning any serious causes of blurred vision after lasik. It’s because fortunately lasik is quite a safe procedure. But there are two notable things to mention that can cause blurred vision after lasik.
Lasik Flap Problems
This includes a fold or wrinkle in the lasik flap. This also includes any dislocation of the lasik flap after the surgery. Both of these two things can cause additional blurred vision.
The likelihood of these issues dramatically decrease the further you get out from lasik. The risk is the highest within the first 24 hours. Once the surface of the cornea heals over and the scratchiness subsides, this risk starts to decrease and continues to decrease as the eye continues to heal.
This is one reason why there are certain precautions after lasik; the goal is to prevent any rubbing of the eyes.
But fortunately, issues with the lasik flap can be fixed. Your surgeon simply uses sterile water to “re-float" the lasik flap back into position. Depending on what needs to be done, the recovery after this “re-float" procedure can be as quick as a day or as long as a week until the vision is restored.
Also check out Everything You Need To Know About Flap Dislocation After Lasik
Infection
Developing an infection underneath the lasik flap is extremely rare (it occurs less than 0.035% of the time), but it is likely the most serious cause of blurred vision after lasik.
Once again, many of the precautions after lasik are designed to further reduce this risk even more.
Infections can be treated. This could require additional eye drops. This could also require another procedure to lift and “wash" away the infection from underneath the lasik flap.
And when treated, the odds are still great that the infection doesn’t cause any lasting significant vision loss.
Unrelated Issue to Lasik
Finally, it’s important to mention that after lasik, your eyes are still eyes. And just how random eye disease can hit anyone, it can also occur after having had lasik done. You may have blurred vision from some unrelated cause.
A good example of this is a retinal detachment. The retina is the part of the eye that collects all the light information from what you see and passes that information to the brain to interpret. If this retina detaches, you can lose vision (especially if the retina detaches within the center part of your vision).
Highly nearsighted individuals are at a greater risk of developing a retinal detachment in their lifetime. It also happens to be that highly nearsighted individuals are often treated with lasik. While lasik doesn’t increase the risk of retinal detachments, they can still occur due to normal risk factors of having a highly nearsighted eye.
Thus, if you are experiencing blurred vision after lasik, it’s important to have a doctor take a look to determine what’s actually going on.
Summary
Having residual prescription is the most common cause of blurred vision after lasik. But there are a few other important things to know about. The good news is that there are ways that these other conditions can be treated to correct this blurred vision.
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