Correcting Vision With Refractive Eye Surgery
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Correcting Vision With Refractive Eye Surgery

Almost half of the population has vision problems, such as difficulty seeing objects close up, far away, or both. Less than a decade ago, 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 2/3 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

The Procedure

  • 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 15 minutes.

It will take a couple of days for the epithelium to regrow over the cornea. For the first 3-5 days, vision may be blurred. Functional vision returns in one to three weeks, and vision stabilizes over the next three to 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 preformed 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 Procedure

  • 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.

You should see some improvement almost immediately after the surgery, with continued improvements over the next couple of weeks. It can take up to three months to achieve the full effect. The related procedure termed “LASEK” is also used by many ophthalmologists and is probably similar in terms of postoperative recovery and outcome.

Radial Keratotomy (RK)

RK is a surgical procedure using a sharp knife, not a laser, to reshape the cornea. It is not performed as often as it once was due to the more reliable laser-surgery methods. It is recommended for people with:

  • Low to moderate myopia

The Procedure

  • The eye is anesthetized before surgery with eye drops.
  • Using a diamond knife, the surgeon makes a series of incisions in the cornea.
  • The incisions radiate out from the cornea, much like the spokes on a wheel. The number of incisions can range anywhere from 4-16.
  • Total procedure time is about 15 minutes.

The incisions flatten the cornea, allowing for a more normal curvature, which can reduce myopia.

Recovery time is usually about a week with vision stabilizing over the next 3-6 weeks.

Astigmatic Keratotomy (AK)

AK is used to treat astigmatism. The procedure is similar to RK, but the arc-shaped incisions are made across the cornea, rather than radially. AK is sometimes performed in conjunction with RK.

Intrastromal Corneal Ring Segments (ICRS) and Other Procedures

ICRS has the advantage of not involving the central part of the cornea, so it has less risk of causing undesirable side effects. This procedure places a plastic ring within the outer part of the cornea, providing a kind of splint that flattens the cornea. It is only useful for mild myopia, so its application is quite limited.

Other procedures that are being used more commonly include clear lens extractions, phakic intraocular lens insertions, and conductive keratoplasty. 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. LASIK and LASEK procedures probably remain the most commonly used treatments.

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, irregular astigmatism (permanent warping of the cornea), and an inability to wear contact lenses
  • Corneal infection—Immediate medical treatment is necessary.
  • 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.
  • A decrease in contrast sensitivity, crispness, or sharpness—Even though you may have 20/20 vision, objects may appear fuzzy or grayish.
  • Problems with night driving that may require glasses

The following side effects are possible, but usually disappear over time. In rare situations, they may be permanent.

  • Discomfort or pain
  • Hazy or blurry vision
  • Scratchiness
  • Dryness
  • Glare
  • Halos or "starbursts" around lights
  • Light sensitivity
  • Small pink or red patches on the white of the eye

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.

RESOURCES:

American Academy of Ophthalmology
http://www.aao.org/

American College of Eye Surgeons
American Board of Eye Surgeons
www.aces-abes.org/

CANADIAN RESOURCES:

Eyesite.ca
http://www.eyesite.ca/

Health Canada
http://www.hc-sc.gc.ca/index_e.html/

References

Duffey RJ, Leaming D. US trends in refractive surgery: 2003 ISRS/AAO survey. J Refract Surg. 2005;21:87-91.

PRK: the original laser eye surgery. All About Vision website. Available at: http://www.allaboutvision.com/visionsurgery/prk.htm. Updated October 2007. Accessed September 4, 2008.



Last reviewed June 2008 by Eric L. Berman, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.


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