What Is LASIK and How Does It Work?

BY: Kate Raftery |Jun 20, 2016

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Much of our writing for eye-surgery deals boils down to one question: what is LASIK? Unfortunately for me, whenever I read or write about it, I get a little squirmy. I experience visceral discomfort just at the idea of a procedure in which a laser is used to reshape the cornea under a small flap made in the eye’s surface. But then again, I have a thing about eyes—I also can’t watch people put in contact lenses.

To get over my phobia sooner rather later—and answer some common questions of prospective patients—I decided to become as knowledgeable about LASIK eye surgery as one can be without becoming an MD. (Or an ophthalmologist. There’s only so much time in the day, you know.)

First things first: what is LASIK?

LASIK is an outpatient procedure that treats nearsightedness, farsightedness, and astigmatism. This type of surgery corrects refractive errors by reshaping the cornea to adjust the eye’s focusing ability.

Wait, what’s the cornea?

The cornea is the eye’s transparent outermost layer. According to the National Eye Institute, “when light strikes the cornea, it bends—or refracts—the incoming light onto the lens. The lens refocuses that light onto the retina, which starts the translation of light into vision. The retina converts light into electrical impulses that travel through the optic nerve to the brain, which interprets them as images.”

It’s helpful to think of the cornea as the lens of a camera, focusing light onto film. When the light is refracted incorrectly onto the film or the retina, you get a blurred image. Prescription glasses and contact lenses compensate for these refractive errors, whereas LASIK seeks to eliminate them.

How does the shape of the cornea change?

  • If you’re nearsighted, your cornea is too steep, causing distant objects to appear blurrier than close ones. LASIK flattens it out.
  • If you’re farsighted, your cornea is too flat, causing near objects to appear blurrier than distant objects. LASIK forces it to become steeper.
  • If you’re astigmatic, your cornea is irregularly shaped, causing distorted, blurry vision. LASIK makes it smoother and more symmetrical.

How does LASIK work?

Basically, a laser precisely vaporizes microscopic amounts of corneal tissue to reshape the curvature of the cornea based on your precise prescription. Here’s what goes down:

Micro view:

This diagram shows what’s happening to the eyes

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1. A surgeon numbs your eyes with anesthetic eye drops. An instrument gently holds your eyes open.

2. As a soft suction ring holds the eye in place—briefly dimming your vision—the surgeon uses a tiny blade or a laser to create a circular flap on the outermost layer of your cornea. The flap acts like a hinged window into the cornea’s next layer, called the stroma.

3. Once the corneal flap is lifted and folded back, a different, specialized laser then reshapes the stroma. But it doesn’t beam into your eye willy-nilly—it vaporizes certain cells in the stroma according to your exact prescription. You won’t feel the laser itself, but you may detect an odor similar to burning hair as the laser ablates corneal tissue.

4. When the laser finishes, the surgeon closes the corneal flap. It will remain shut on its own and heal over time—no weird eye stitches needed. Overall, the procedure lasts for about 10 minutes per eye, and less than a minute of that involves the actual lasering.

Macro view:

This LASIK eye surgery video shows what the patient experiences

Is LASIK safe?

We devoted an entire article to this question. And the short answer is yes. The surgery itself should be painless. And while most patients experience uncomfortable side effects for a few days after the surgery—like dry, itchy eyes and hazy vision—very few people suffer these effects long term.

Who are LASIK’s ideal candidates?

A doctor will determine whether you’re qualified for the procedure. Generally, if you have healthy corneas of normal thickness, most doctors treat nearsightedness, farsightedness, and astigmatism that require prescription lenses of average strength to correct. However, some pre-existing conditions can disqualify prospective patients, including chronic dry eye, cataracts, glaucoma, and some autoimmune disorders.

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