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Which Is Better, Lasik vs PRK?
Nothing is as hotly as debated as a topic (at least in the world of vision correction surgery) as the age old discussion of which is better: Lasik vs PRK? Is there is a clear winner in this battle of heavyweight champs? Let's get into the ring to see which procedure emerges as the victor.
Two champions enter the ring
Lasik and PRK are very similar procedures. They both have the same goal in mind: correcting your vision. Both have been well studied and tested over the years.
Lasik is perhaps the much more well known of the two procedures. During lasik, a small lasik flap is created just beneath the surface of the cornea. This flap is folded back and a different laser is used to change the curvature of the cornea to correct vision (see also How Does Lasik Work?). The creation of lasik flap is the ONE difference between lasik and PRK. PRK uses the exact same laser for the vision correction part, it's just done with NO flap creation.
For the laser to work to correct vision, the laser energy must be applied to the rigid framework of the cornea called the stroma. Lasik works by creating a flap directly to the level of the stroma. Directly above the stroma, on the surface of the cornea, there exists a thin layer of cells called epithelial cells. During PRK, these surface epithelial cells are removed to allow the laser to treat the stroma below.
Layers of the cornea; Image by StemBook (CC BY 3.0) / modified from original
Side Note: Over the years, surgeons have developed "new procedures" which are just slightly different variants of PRK. Procedures such as Epi-Lasik and LASEK all fall under the umbrella of PRK (and in general make it more confusing for you to actually figure out what procedure you are getting).
Ding Ding Ding 🔔, time to start the fight
Round 1 - The Evaluation
Both PRK and lasik stare each other down intensely as they figure out their gameplan.
Many people are candidates for either lasik or PRK. There may be a few patients who are ONLY candidates for PRK (but the reverse is generally NOT true; it's very uncommon for someone to only be a candidate for lasik but NOT PRK). PRK can be favored over lasik in 3 main scenarios:
- Lasik creates a flap within the cornea. This flap requires a certain amount of thickness to the cornea. Performing the vision correction treatment also requires a certain amount of thickness. To perform a safe laser eye surgery, there are limits to how much cornea can be modified. If the cornea doesn't have enough thickness to do both the flap and the treatment, than lasik just wouldn't be the safest procedure. PRK, however, requires less cornea thickness to perform because there is no flap.
- Patients who have had lasik performed long ago are often better candidates for PRK if they require another treatment. Performing PRK avoids having to create two lasik flaps within the cornea and risking the potential of those two lasik flaps intersecting each other. While in some cases this can be done, PRK remains the more straight-forward approach.
- People who get hit in the eye repeatedly (like boxers for example), will want PRK over lasik. With no lasik flap to disrupt, there is no concern about having any flap issues.
After the evaluation, however, neither Lasik nor PRK really gains an additional edge before the procedure day. Lasik and PRK are frequently the same price. There is no difference between the pre-op workup for either PRK or lasik. Both require the same testing done beforehand. Both have the same amount of visits and same requirements.
So Round 1 ends with PRK taking a slight edge over lasik (due to being an option for more people than lasik)
Round 2 - The Procedure
Round 2 is a very quick round. Both procedures are super quick. Both procedures are also painless and easy to go through. But PRK comes out with another slight edge over lasik!!
Lasik takes just a little bit longer than PRK. PRK has that additional step of removing the epithelial cells, but lasik has the additional step of creating the lasik flap. The act of creating the lasik flap and folding back that lasik flap for treatment is going to take just slightly longer than the PRK step of removing the epithelial cells. What is slightly longer? Maybe a minute or two. So in reality it is almost a tie, but PRK still holds the slight edge time-wise.
PRK also holds a very slight edge in probability of completion of procedure. With PRK, once you get started with the procedure, there is an almost zero chance that there will be any roadblocks preventing you completing the procedure that day (I say almost zero but I can't think of anything that would prevent PRK from being completed). The lasik flap creation step of lasik adds just a few more variables which can prevent the full completion of lasik on the same day.
- To create a perfect lasik flap, a suction ring rests and suctions onto your eye. This step is necessary to prevent eye movements from causing any issues with the creation of the lasik flap. This suction ring is designed to fit all types of eyes; but not all eyes are created equal. Rarely, this suction ring can run into an eye which doesn't fit very well. If suction can't be obtained, lasik can't be performed and they eye will ultimately have to be treated with PRK. Rarely, the suction ring may seem like it has good suction but the suction breaks during the treatment. In this case, sometimes lasik can be continued on the same day but if not then PRK can be done at a later date.
- To make a lasik flap with a laser, the laser creates tiny microscopic air pockets in the 3D dimensional shape of the flap. Once the air pocket is created, the remaining air is redirected to the edge of the cornea and out of the way. Rarely, this air can be directed into the anterior chamber and inside of the eye. Not an issue, air dissolves with time, except that this air can prevent the laser from tracking the eye while performing the vision correction treatment. To prevent eye movements from being an issue, the laser measures and tracks your pupil during a laser treatment. If an air bubble forms within your eye, this air bubble blocks the view of the pupil and can prevent the laser from registering your pupil. If this happens, the lasik treatment will have to be postponed until the bubble dissolves; this could take hours and often the lasik treatment would just be pushed to the next day.
Given these extra variables, lasik has a slightly less chance in the probability of completion of procedure than PRK. Not any issues in the long-run but annoying and inconvenient in the short-run. That being said, these things are rare, but PRK still wins the round on a slight margin!
Round 3 - The Immediate Recovery
PRK starts to get cocky about it's first two round wins. Lasik, not backing down goes in for a knockout blow against PRK. PRK recovers but not before lasik takes a commanding lead.
The largest difference between lasik and PRK is the initial recovery. The sole reason lasik was created in the first place and the reason the lasik flap exists is to improve recovery.
The cornea is a very sensitive structure. If you have gotten a scratch on your eye before then you already know this. Any scratch on the eye can be painful. Lasik was designed to create as minimal scratch as possible. There is still a scratch after lasik (see also Does Lasik Hurt?), but this heals up pretty quickly within the first few hours following the procedure.
PRK is much much different. During PRK, the epithelial cells are removed from the surface of the cornea. These epithelial cells provide a protective barrier to the sensitive cornea below. This creates a large scratch or abrasion on your cornea. Until this abrasion heals over, you will feel pain and discomfort after PRK. This pain lasts about 4 days (and occasionally a little longer). To help with this pain, a contact lens is placed on the eye to serve as an artificial barrier. This helps a lot of people quite a bit. Instead of severe pain, the contact lens reduces it to a dull mild-moderate discomfort. But everyone responds differently to PRK. Some people will have just a few symptoms, some people are on the other end of the spectrum and have bad discomfort. PRK just isn't very fun to recover from.
On top of this, it takes longer for the vision to be restored after PRK. Lasik enjoys very rapid improvement in a vision. Within the first 24 hours, everything has sharpened up considerably for most people with lasik. PRK takes much longer. Immediately after PRK, you will actually notice some quick improvements in vision. With the epithelial cells removed from the treatment area, you are looking through a clear window; those epithelial cells aren't interfering with your vision. As those epithelial cells grow to heal up the abrasion, these cells start to grow into the center of your vision. The edge of the growing epithelial cells isn't perfectly flat and transparent and this creates a blur as you try to look through them. The blurry vision peaks right around day 4-5 when the growing epithelial cells meet in the middle of your cornea and form a small ridge (the same time the pain with PRK stops). Following this, the vision continues to improve over the course of the rest of the week as the cornea continues to become smooth, flat and transparent.
The immediate recovery after PRK is a much longer process than lasik.
To be fair, lasik isn't perfect. In rare cases there can be extra inconveniences after lasik related to the lasik flap. Early after lasik, there can be the possibility that rubbing the eye shifts the lasik flap out of position. Also a rare possibility is that extra inflammation can develop underneath the lasik flap requiring additional treatment. But the vast majority of lasik patient never have to experience these extra inconveniences and when treated the long-term outcome is unaffected. (see also What Are The Risks Of Lasik Surgery?)
Round 4 - The Long Term Recovery
PRK is stunned, but doesn't quit. But you can tell that PRK is getting a little tired and fatigued. Round 4 lasts the longest of any of the rounds. Lasik takes advantage of this weariness.
One week out after PRK, the vision hasn't fully healed up to the full potential. The center of the cornea isn't as fully clear or transparent as it will be. It's gotten pretty close but there is still more to come in the next few weeks. When we get to the one month mark after PRK, we are almost there. But at some point between the first week and the first month, most people stop noticing the gradual improvement in their vision. In their interpretation, their vision has fully healed up. So despite the fact that vision after PRK continues to improve over the course of the first few months, the vast majority notices that things are good within the first month after PRK.
- Edge lasik
Both lasik and PRK are very accurate procedure. Both will work to correct your vision and get you out of glasses and contact lenses. And once healed up, both are highly accurate. In fact, there isn’t really any statistically significant difference in vision or prescription between both lasik and PRK both in the short term or long term. Just the difference in how long it takes to get there.
- It’s a tie
Both lasik and PRK patients will have some extra dry eye after the procedure. Dry eye after lasik is caused by the disruption of tiny little nerves within the cornea. These nerves sense when the cornea is dry and signal to the tear glad to produce more tears. Within the first 6 months following lasik, these nerves regenerate to restore normal function. While it takes about 6 months for these nerves to regenerate, most people after lasik really notice the dryness for just about the first month. Some people, especially those with preexisting dryness or contact lens intolerance can notice it for a few months longer, typically about 2-4 months. But when dryness is properly treated before and after lasik, it's rare that it last much longer after that.
One common thought is that PRK can improve upon the dryness after lasik. After-all, by keeping the treatment limited to the surface, PRK avoids affecting a larger percentage of the cornea and disrupting extra cornea nerves. And yes, while this is technically true, PRK doesn't get spared from dryness after the procedure. A significant factor in the propagation of dryness is inflammation. Inflammation prevents the normal production of tears on the eye. The more inflammation there is on the surface of the cornea, the greater amount of dryness that results. When you have an abrasion on the surface of the eye (like what you have after PRK), the eye responds to this by creating lots of inflammation. This inflammation adds discomfort but also contributes to extra dry eye after PRK. As a result, PRK patients will still have dry eye and in some cases can have even more dry eye than lasik patients. If your goal is to reduce the amount of dry eye after lasik, PRK isn't the answer.
- Another tie
Safety / Stability
The biggest concern about lasik is about the creation of the flap. Does the flap serve as a weak-point for the rest of your life? For some patients as mentioned before, such as boxers, yes it does. If you expect to take a lot of trauma to the head and eyes, you won't want to have a lasik flap. (Although the risk is still extraordinary low; see also What If I Get Punched In Eye After Lasik?). For just about everyone else, the flap doesn't present any significant concern.
Lasik flaps are created differently today than how lasik flaps were created in the past. Lasik flaps used to be created with a blade. A blade is only capable of creating a single plane to the lasik flap. Today, lasik flaps are created with lasers. A laser is able to create a complex 3D flap (when you see the marketing term 3D lasik, this is what it typically is referring to; or at least it should be). Like a manhole cover, the 3D created lasik flap fits and aligns better on the surface of the cornea. The edges of the flap can also be created in a way to allow the lasik flap to lock in place like a puzzle piece. This creates more strength and stability at the edge of the lasik flap. Laser created lasik flaps are much more difficult to disrupt than those created with blades.
It's extremely rare to not only be poked in the eye but also in just the right way to mess with the lasik flap. But if it does happen, it can be fixed. The lasik flap is simply just repositioned through another procedure. Any trauma that really causes an issue where the lasik flap can't be repositioned is likely to cause issues with your eyes regardless of which procedure you had done. The lasik flap just isn't much of a concern with today's modern lasik.
- But given that PRK has zero concern of a flap and zero is less than "not any significant concern", edge PRK
And the winner is...
And it's over; image by Biser Todorov, CC BY-SA 4.0, via Wikimedia Commons
It's been a hard fought fight between two great procedures. So which is the clear winner? All things being equal, lasik tends to be a better procedure than PRK. But of course in life, everything isn't always equal. For some patients, PRK makes the most sense. But for most others, lasik makes the most sense. Regardless of which procedure you choose in the end, the important point is both work very well to correct your vision and it's pretty awesome getting out of those glasses and contact lenses.
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