What does LASIK eye surgery involve?

There are several variations of laser refractive surgery. LASIK is the best known and most commonly performed. Many articles, including this one, will use the term "LASIK" to refer to all types of laser eye surgery.

Typically, images are focused on the retina in the back of the eye. With nearsightedness, farsightedness or astigmatism, they end up being focused either in front of or behind the retina, resulting in blurred vision.

• Nearsightedness (myopia) is a condition in which you see nearby objects clearly, but distant objects are blurry. When your eyeball is slightly longer than normal or when the cornea curves too sharply, light rays focus in front of the retina and blur distant vision. You can see objects that are close more clearly, but not those that are far away.
• Farsightedness (hyperopia) is a condition in which you can see far objects clearly, but nearby objects are blurry. When you have a shorter than average eyeball or a cornea that is too flat, light focuses behind the retina instead of on it. This blurs near vision and sometimes distant vision.
• Astigmatism causes overall blurry vision. When the cornea curves or flattens unevenly, the result is astigmatism, which disrupts focus of near and distant vision.

Traditionally, blurry vision is corrected by bending (refracting) light rays with glasses or contact lenses. But reshaping the cornea (the dome-shaped transparent tissue at the front of your eye) itself also can provide the necessary refraction and vision correction.

Before a LASIK procedure, your eye surgeon will assess detailed measurements of your eye and assess the overall health of the eye. You may be instructed to take a mild sedative medication just prior to the procedure. After you are lying comfortably on an operating table, eye-numbing drops will be administered. Then he or she will use a special type of cutting laser to precisely alter the curvature of your cornea. With each pulse of the laser beam, a tiny amount of corneal tissue is removed, allowing your eye surgeon to flatten the curve of your cornea or make it steeper.

Most commonly, the surgeon creates a flap in the cornea and then raises it up before reshaping the cornea. There are also variations in which a very thin flap is raised or no flap is used at all or no flap at all, is raised. Each technique has advantages and disadvantages.

Individual eye surgeons may specialize in specific types of laser eye procedures. The differences among them are generally minor, and none are clearly better than any others. Depending on your individual circumstances and preferences, you may consider:

• Laser-assisted in situ keratomileusis (LASIK). Now the most commonly performed eye laser surgery, LASIK involves creating a partial-thickness corneal flap and using an excimer laser to ablate the bed of the cornea. The flap is then placed back into its original position. Discomfort after surgery is minimal, and vision recovery usually takes place in 1 to 2 days.

• Photorefractive keratectomy (PRK). With PRK, rather than forming a flap, the top surface (epithelium) is scraped away. This corneal abrasion takes three or four days to heal, resulting in moderate pain and blurred vision in the short term.

It was thought that these drawbacks were outweighed by the theoretical advantage that PRK was safer for people who are more likely to be struck in the eye — for example, those involved in contact sports, law enforcement or the military. But even with standard LASIK, the risk of eyeball rupture is still very low, so there is probably no significant advantage with PRK. LASIK is also a better option than PRK for correcting more severe nearsightedness (myopia).

• Laser-assisted subepithelial keratectomy (LASEK). LASEK is similar to LASIK surgery, but the flap is created by using a special cutting device (microkeratome) and exposing the cornea to ethanol. The procedure allows the surgeon to remove less of the cornea, making it a good option for people who have thin corneas. For people at greater risk of eye injuries, LASEK does not have any significant advantages over LASIK.
• Epithelial laser-assisted in situ keratomileusis (epi-LASIK). In an epi-LASIK procedure, your surgeon separates the epithelium from the middle part of the cornea (stroma) using a mechanized blunt blade device (epikeratome) and reshapes the cornea with a laser. This procedure is similar to LASEK.
• Small-incision lenticule extraction (SMILE). This newer type of refractive surgery reshapes the cornea by using a laser to make a lens-shaped bit of tissue (lenticule) below the cornea surface. Once the lenticule has been used to reshape the cornea, it is then removed through a very small incision.

• Intraocular lenses. Corrective lenses can be surgically inserted in the eye (intraocular lenses) to improve vision. This is routinely done as part of cataract surgery (in which the old, cloudy natural lens is removed). It may also be an alternative to LASIK for older adults who may need cataract surgery in the future.

  Younger people with high degrees of nearsightedness that cannot be satisfactorily treated with corrective lenses also may be offered intraocular lenses. But these are not a routine option for most people.

• Bioptics. Bioptics combines one or more techniques, such as intraocular lenses and LASIK, to treat nearsightedness or farsightedness.