How does laser eye surgery work? – Dan Reinstein

In 1948, Spanish ophthalmologist
Jose Ignacio Barraquer Moner was fed up with glasses. He wanted a solution for blurry
vision that fixed the eye itself, without relying on external aids. But the surgery he eventually devised
was not for the faint of heart. Barraquer began by slicing off the front
of a patient’s cornea and dunking it in liquid nitrogen. Using a miniature lathe, he ground the
frozen cornea into the precise shape necessary to focus
the patient’s vision. Then he thawed the disc, and sewed
it back on. Barraquer called this procedure
keratomileusis, from the Greek words for “carving”
and “cornea.” And though it might sound grisly,
his technique produced reliable results. So how did Barraquer’s surgery work? Keratomileusis corrects what are called
refractive errors: imperfections in the way the eye focuses
incoming light. Ideally, the cornea and lens work
together to focus light on the surface of the retina, but several kinds of refractive errors
can impair this delicate system. In people with myopia,
or short-sightedness, a steep cornea focuses light just short
of the retina. Those with hyperopia, or far-sightedness,
have the opposite problem: light is focused too far
beyond the retina. And in people with astigmatism,
the cornea has two different curvatures which focus light at two distances and
produce blurry vision. Even those with perfect vision will
eventually suffer from presbyopia, or “aging eyes.” As the proteins in the lens age, they
slowly increase its size. By an adult’s mid-40’s, the lens is too
large to easily change shape and shift focus. Glasses and contact lenses bend light
to compensate for these refractive errors. But, as Barraquer’s procedure shows, we can also alter the shape
of the cornea itself; moving the focal point backwards,
forwards, or pulling a divided image together. And thankfully, modern eye surgeons can
sculpt the cornea with far less invasive tools. In corrective laser eye surgery, surgeons
rely on excimer lasers. These tools are accurate enough to etch
words into a human hair. To safely accomplish these
ultra-fine incisions, they use a technique called photoablation. This allows the laser to essentially
evaporate organic tissue without overheating
surrounding eye tissue. So how does laser eye surgery
actually work? The first step is to separate a thin layer
from the front of the cornea. This can be done with either a flat,
wide blade, or a femto-second laser that produces millions of tiny plasma
bubbles to create a plane beneath
the corneal surface. Surgeons then lift the flap to expose the
inside of the cornea. Guided by the refractive error and the
shape of the cornea, the excimer laser robotically sculpts the
exposed corneal bed into the correct shape. This process usually takes less than 30
seconds for each eye. Finally, the flap is closed, and its edges reseal themselves
in just a few hours. Because the lasering is done on
the eyeball itself, it’s described as “in situ,” or “on site.” Its complete name is “laser in-situ
keratomileusis” – but you probably know it as LASIK. Essentially, this technique carves a
patient’s contact lens prescription onto their cornea. Like any surgical procedure, LASIK comes with certain risks. Some patients experience slightly blurred
vision that can’t be corrected by glasses. But the technique is currently about
as likely to damage your eyes as wearing daily disposable contact
lenses for one year. Today, a technique called SMILE enables
surgeons to sculpt the cornea through even smaller incisions – further reducing recovery time. And lasers aren’t just correcting the
three types of refractive errors – this technology can also
restore aging eyes. In a technique called Laser
Blended Vision, surgeons adjust one eye to be slightly
better at distance vision and the other to be better
at close range vision. The difference between the two eyes is
small enough that most patients can merge their vision, allowing both eyes to work
together at all distances. Advances in laser technology continue
to make vision correction surgery more effective and accessible. One day soon, Barraquer’s vision of a
world without glasses may finally come true.


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