Laser eye surgery (LASIK/LASEK)
by Chris Woodford. Last updated: June 14, 2020.
Don't stare at the Sun! It's something we all learn at a very early age: everyone
knows it can blind you. So what's the deal with laser eye surgery (or
LASIK/LASEK, as it's properly called)? If looking at the Sun is harmful,
how can staring into a blindingly bright laser
improve your vision so you no longer need glasses or
contact lenses? The difference between the Sun and an eye-surgery laser is simple:
the surgery involves a meticulous procedure where a laser fires into your eye for nanoseconds at a time
under precise, computer control. Let's take
a closer look!
Photo: LASIK/LASEK surgery may be able to improve your vision, but
it's not suitable for everyone—and you need to be aware of the risks.
Please note that this is an artistic representation of laser surgery, not an actual illustration
of what's involved.
Why might you need eye surgery?
Photo: Having eyeglasses can be very tedious. Fortunately, the ones you end up with are generally much more
comfortable than the adjustable ones you get in opticians! Photo by courtesy of National Eye Institute, National Institutes of Health.
If you've worn eyeglasses or contact lenses for years, laser eye surgery can seem a
very attractive option. Just imagine being able to see clearly
without those clumsy optical attachments stuck in front of your eyes!
The first to understand is how the surgery does away with the need for
The reason you need extra lenses is because the natural
lenses inside your eyes don't do their job properly.
When light from distant objects reaches your eyes, the lenses (one
in each eye) are supposed to refract (bend) the rays so they
focus on your retina. But that doesn't always happen:
- If you're short-sighted (myopic), the
muscles in your eye don't relax enough, so the lens is slightly too
fat and too strong. As a result, it brings light rays in to focus too soon,
slightly in front of your retina, making distant things look blurred.
- If you're long-sighted (hyperopic), you have the opposite problem. Your
eye muscles can't make the lens fat and strong enough. Light rays
passing through the lens aren't bent inward enough so, by the time
they reach your retina, they haven't quite come together in focus.
When you wear eyeglasses or contact lenses, the extra bit of glass or plastic
compensates for the lenses in your eye so light rays focus perfectly on your retina.
Artwork: Eye anatomy: the main parts of the human eye. The cornea at the front is the bit we're interested in when it comes to laser eye surgery.
What is laser eye surgery?
Now in theory, if we could operate on people's eyes to change the shape of their
lenses, we could correct eye problems like this very easily. The
trouble is, the lens is not on the outside of the eye: it's not
easily accessible to an eye surgeon. Why not? Well, in front of the lens there's a
thin, transparent protective coating called the cornea that
you'd have to remove first. But here's a bit of luck. Since the
cornea is curved, and not made of air, it also has an effect on light
rays. In other words, it too behaves like a mild lens at the front of
your eye. So the theory behind laser eye surgery is to change the
shape of the cornea, very slightly, to compensate for problems in the
lens behind it.
The medical prefix for anything to do with the cornea is kerato; keratitis, for
example, is the name given to an inflammation of the cornea, having
surgery to remove part of your cornea is called a keratectomy, and
reshaping your cornea is keratomileusis. So now you can see where
surgeons got the name LASIK from: it stands for Laser-Assisted
In-Situ Keratomileusis. In other words, using a laser to reshape your cornea.
The alternative procedure called LASEK stands for
Gulp. So what do these horrible-sounding things actually mean?
Photo: Corneal topography: Some time before you have laser eye surgery, you'll have an eye examination to establish how much treatment your corneas need. During that session, a computerized machine like this will make a map of your cornea so the surgeon can figure out which parts of the tissue need to be removed. Photo by Tony Tolley courtesy of RAF Lakenheath, US Air Force, and Defense Imagery.
What does it involve in practice?
Newspaper and magazine advertisements paint a seductive picture of laser eye surgery as a
simple walk-in procedure: walk-in with glasses like the bottoms of
wine bottles; walk-out with 20–20 vision. This is really quite a
misrepresentation. First, laser surgery isn't suitable for everyone and
absolutely doesn't guarantee perfect vision.
Second, it's far from such a simple procedure: it typically involves a
lengthy period of preparation before the laser operation and an even
longer period of recovery lasting six months or more after the operation is done. Before the
surgery, for example, you have to stop wearing contact lenses and
eye makeup. If you wear hard lenses, you have to cease wearing them
for weeks or even months before the surgery can take place (the exact period
depending on how long you've been using them).
Photo: An eye surgeon carries out LASIK surgery. Photo by Larry A. Simmons courtesy of US Air Force.
The operation itself is relatively simple and it's easy to understand. First, your eye is treated
with an anesthetic, then your eyelids are gripped and held open by a
suction frame. The same device pulls on the cornea and holds it
securely in place ready for the surgery. It's not exactly painful, though
it's not comfortable either. Next, using tiny bursts of
powerful light lasting no more than a few nanoseconds, the laser cuts
a flap in your cornea. (In some procedures, the flap is cut by a
microscopic knife called a microkeratome blade.) Think of the flap as a bit
like a small door in the surface of the cornea: it's cut on three
sides but the fourth side is left attached to form a kind of hinge. The flap is then lifted
up and folded back on the hinge to expose the inner corneal tissue
underneath. Under computer control, the laser then reshapes the
cornea under the flap. Once that's done, the flap is replaced and it
will slowly reattach itself without any need for stitches or surgical
That's pretty much it—although you can't expect an instant improvement in your vision.
First, you have to recover from the operation itself. You have to
take antibiotics and other eyedrops to prevent infections and a
syndrome called "dry eye." You also have to rest more and sleep
with an eyeguard for several weeks to prevent damage while
your eye recovers. You're not allowed to wear eye make-up, for the first few days,
or take part in strenuous sports, for the first few weeks. Swimming
pools and hot-tubs are usually off-limits for a couple of months.
LASEK evolved from an earlier kind of laser treatment called photorefractive keratectomy (PRK), but
is considered less painful. In simple terms, LASEK is a more superficial and less drastic treatment than LASIK; technically, it's referred to as a "surface ablation procedure," which involves removing some of the epithelium (surface cells) of the cornea. For that reason, it's generally considered safer than LASIK and less prone to complications. However, views differ on whether LASEK or LASIK is the better treatment and there is
still no definitive answer. For example, a 2017
Cochrane review of numerous published studies concluded only that "there is uncertainty in how LASEK compares with LASIK in achieving better refractive and visual results in mildly to moderately myopic participants."
Is laser surgery a good idea?
Since laser eye surgery became available in the early 1990s, millions of people have benefited
from a permanent improvement in their vision. Although few long-term
studies have been done, over 90 percent of people who've had
laser surgery reputedly achieve perfect or much-improved vision. Not
surprisingly, a similar percentage of patients say they're satisfied
with the results of their operation. Even so, laser eye surgery is by
no means a miracle cure for bad eyesight, as government health
agencies and consumer groups around the world have been at pains to
point out. If you're considering having this treatment, be
sure you're properly informed about everything it entails and
make sure you have realistic expectations.
Photo: Laser surgery is a meticulous medical procedure; even so, there are risks
and potential side-effects—and you won't be saying goodbye to eye charts forever: it's important to have your eyes examined regularly even after treatment. Photo by Brian Ferguson courtesy of
US Air Force.
The first thing to note is that laser treatment is not suitable for everyone.
While it may suit people with relatively mild short sight, for example, it's
less suitable for those with very poor vision and it
cannot address the gradual deterioration in close-up vision
(presbyopia) that most people experience when they get older. A
significant proportion of patients need a second operation called a
retreatment, so you should be prepared for that possibility. It's
also important to realize that the recovery from laser-surgery can be
uncomfortable and protracted. Some people experience uncomfortable or painful side-effects
for months after their operation (you'll often hear about a common phenomenon called "dry eyes")
and complications such as dislocated ("slipped") or folded flaps.
A small number report that the operation has made their vision worse—and there have been numerous claims for damages (search for "LASIK legal claims" and you'll find lots of eager lawyers ready to sue for medical negligence). Having said that, lots of people will tell you that having laser eye surgery was the best thing they ever did.
The key messages are these:
- Remember that this is a serious surgical procedure and isn't something to be undertaken lightly. It's far more serious than simply opting to switch from glasses to contact lenses, for example.
- Make sure you're fully informed about what the procedure entails and how long it may take you to recover. Don't fall for glossy advertisements and a hard-sell from an optical clinic. Read widely and be sure to get your information from trusted, reputable sources. The US FDA website (see the references below) is a great place to start.
- Be sure you have realistic expectations about the outcome. Your vision may still not be perfect after the operation. You may need a retreatment. In the end, you may still need to wear eyeglasses for driving or some other activities.
- If you decide to go ahead, take pains to check the credentials and reputation of your eye surgeon. Make sure you consider quotes from multiple surgeons and don't automatically opt for the cheapest.