What does LASIK eye surgery involve?

There are several types 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, images are focused either in front of or behind the retina. This results in blurred vision.

• Nearsightedness, called myopia, is a condition in which you see nearby objects clearly, but distant objects are blurry. When your eyeball is slightly longer than average or when the cornea curves too sharply, light rays focus in front of the retina and blur distant vision. You can see closer objects more clearly, but not those that are far away.
• Farsightedness, called 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 curvature is not the same across the entire cornea, 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 itself also can provide the necessary refraction and vision correction. The cornea is the dome-shaped transparent tissue at the front of your eye.

Before a LASIK procedure, your eye surgeon will take detailed measurements of your eye and check the overall health of the eye. You may be told to take a mild sedative medication just before the procedure. However, this is not common. After you are lying comfortably on an operating table, eye-numbing drops will be administered. Then your surgeon will use a special type of cutting laser to precisely sculpt the curvature of your cornea. With each pulse of the laser beam, a tiny amount of corneal tissue is removed. This allows your eye surgeon to flatten the curve of your cornea or make it steeper.

In LASIK, the surgeon creates a flap in the cornea and then raises it up before reshaping the cornea. There are other types of laser refractive surgery that may not use a flap. 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. Some surgeons feel creating a flap in LASIK poses a slightly higher risk compared to procedures that don't involve a flap. Depending on your 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 reshape 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, called the epithelium, is removed. This corneal abrasion takes 3 to 4 days to heal, resulting in mild to moderate pain and blurred vision in the short term. Visual recovery takes longer in PRK than it does with LASIK.

  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 cornea flap dislocation is still very low, so there is probably no significant advantage with PRK. PRK may be a better procedure for those with thin corneas.

• 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, called a lenticule, below the cornea surface. Once the lenticule is created, it is removed through a small incision, thus changing the shape of the cornea.

• Intraocular lenses. Corrective lenses can be surgically inserted in the eye to improve vision. These intraocular lenses are routinely done as part of cataract surgery (in which the old, cloudy natural lens is removed). Intraocular lenses also may 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.

• Intraocular Collamer Lenses (ICLs). This is a soft polymer and collagen intraocular lens that sits behind your iris but in front of your lens. It has the advantage of treating higher levels of astigmatism and myopia. However, it has other downsides, such as early cataract formation and glaucoma.
• Bioptics. Bioptics combines one or more techniques, such as intraocular lenses and LASIK, to treat nearsightedness or farsightedness.