How the Eye Works | Photorefractive Keratectomy (PRK) | Laser-Assisted in situ Keratomileusis (LASIK) | Alternative Procedures | Making the Decision

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Vision problems are common, including difficulty seeing objects close up or far away—or both. It used to be that glasses or contact lenses were the only option. Today, eye surgery has the potential to permanently correct vision without the use of these visual aids.

How the Eye Works

When you look at an object, the light the object reflects is bent or refracted through the cornea—the clear layer that forms the front window of the eye—and then through the lens, to land on the retina. The nerve endings in the retina send signals through the optic nerve to the brain, where the image is recognized.

The most common eye problems result from refractive errors caused by imprecisely focused light waves. This can be due to a misshaped eyeball, cornea, or lens. The four basic types or errors are:

  • Myopia or nearsightedness—Close objects can be seen clearly, but those distant are blurred.
  • Hyperopia or farsightedness—Distant objects may or may not be seen clearly, but those close are blurred at an earlier age than with other refractive problems.
  • Astigmatism —Both close and distant objects are blurred
  • Presbyopia —The lens, which normally changes shape to focus on objects at varying distances, loses its flexibility; a common process with aging.

Making light rays focus on the retina properly will reduce refractive error. Traditionally, glasses and contact lenses correct the error and enhance vision. Today, more and more people are opting for refractive surgery. By changing the shape of the cornea, which is responsible for most of the eye's focusing power, refractive surgery can decrease or eliminate dependency on glasses or contact lenses. It cannot, however, improve vision beyond what glasses or contacts were able to accomplish. Below are the most common types of refractive surgery.

Photorefractive Keratectomy (PRK)

PRK reduces refractive error by sculpting the surface of the cornea using a laser. It is recommended for people with:

  • Low to moderate myopia, with or without astigmatism
  • Low to moderate hyperopia without astigmatism

  • Prior to the procedure, a map is made of the affected eye's cornea. A computer uses this map to develop a program to guide the laser.
  • The eye is anesthetized before surgery with eye drops.
  • An excimer (cold) laser is used to first remove the layer of the epithelium cells over the eye. The epithelium is the wet outer coating over the cornea.
  • Using the excimer laser and the predetermined program, the surgeon reshapes the cornea by removing thin layers of its outer surface.
  • A soft contact lens is placed over the eye as a bandage.
  • Total procedure time is about 10 minutes.

It will take a couple of days for the epithelium to regrow over the cornea. For the first few weeks, your vision may fluctuate between clear and blurry. Functional vision returns in six weeks, and vision stabilizes over the next six months.

Laser-Assisted in situ Keratomileusis (LASIK)

LASIK uses the same laser as PRK, but adds an additional step that allows the treatment of more significant refractive errors with less postoperative pain and faster visual recovery. For this reason, it has become the most widely performed of the refractive surgeries. It is recommended for people with:

  • Low, moderate, or high myopia, with or without astigmatism
  • Low to moderate hyperopia, with or without astigmatism

  • The eye is anesthetized before surgery with eye drops.
  • A knife, called a microkeratome, is used to cut a flap in the cornea, leaving a hinge at one end of the knife.
  • The flap is folded back to reveal the stroma, which is the middle section of the cornea.
  • Pulses from a computer-controlled excimer laser vaporize a portion of the stroma, and the flap is replaced without the use of sutures.
  • Total procedure time is about 15 minutes.

Removing the tissue on the inside of the cornea changes its shape, which reduces the refractive error.

It can take up to three to six months to for your vision to stabilize. The related procedure termed “LASEK” is also used by many ophthalmologists and is probably similar in terms of postoperative recovery and outcome.

Alternative Procedures

Other procedures that are being used more commonly include:

  • Wavefront-guided LASIK, which measures subtle abnormalities in the surface of the cornea
  • LASEK, which uses a microsurgical instrument to create a flap of epithelial corneal tissue
  • EpiLasik, which separates a very thin sheet of epithelial tissue from the cornea
  • Conductive keratoplasty, which uses a probe that releases controlled amounts of radio frequency to apply heat to the peripheral portion of the cornea
  • Phakic intraocular lenses, which are designed for people with high degrees of refractive errors who aren't candidates for other refractive procedures
  • Refractive lens exchange, which uses an artificial lens to replace your eye's natural lens in order to improve vision

If you are considering refractive surgery, be sure that your surgeon explains all possibilities to you and gives you a convincing reason why the proposed procedure is best for you.

Making the Decision

As with any medical procedure, there are risks involved with refractive surgery. Some risks and possible complications include:

  • Over- or under-correction—If this happens, it can usually be improved with glasses, contact lenses, and enhancements.
  • Corneal scarring
  • Infection or inflammation
  • Loss of best corrected visual acuity—You would not be able to see as well after surgery, even with glasses or contacts, as you did with glasses or contacts before surgery.
  • Visual abnormalities, such as seeing halos or starbursts around lights at night
  • Dry eye
  • Corneal flap complications

Not all people with refractive errors are good candidates for refractive surgery. Talk with your doctor to determine what line of treatment is right for you.