What is photorefractive keratectomy (PRK)?
PRK is a technique used to correct two types of vision-focusing problems:
- Nearsightedness — An excimer laser gently and precisely resculpts the
anterior (front) surface of the cornea. The technique can be used to flatten
the corneal surface or to correct nearsightedness (myopia), a condition in
which the cornea acts as too strong a lens relative to the length of the eye
and focuses images in front of the retina. Flattening the corneal surface
moves the focal point back to the retina.
- Farsightedness — The laser is used to steepen the cornea and strengthen
its lens power so that images that are being focused behind the eye are
moved forward to the retina.
The Food and Drug Administration originally approved use of PRK
for the treatment of myopia from 1 to 7 diopters (a diopter is a unit of
measurement that refers to the lens' ability to focus). Some lasers are now
approved up to 12 diopters of myopia. PRK has also been used for astigmatism
associated with nearsightedness or farsightedness that can be corrected using
the laser or by astigmatic keratotomy.
What are the advantages of PRK?
The advantages of PRK include the following:
- It has a low chance of complications when used for small visual acuity
- It is a highly accurate procedure for the correction of myopia up to 7
diopters. Approximately 80 percent of patients are 20/20 without glasses or
contact lenses at one year; 95 percent to 98 percent are 20/40 or better
without glasses or contacts (the vision required to drive without glasses or
- It is a better procedure than LASIK for some patients who have: too low
a corneal thickness for the level of correction; corneal topography that
puts the patient at higher risk for LASIK-induced complications; epithelial
basement membrane dystrophy of the cornea; or other preoperative issues
discovered during screening for surgery.
What are the disadvantages of PRK?
The disadvantages of PRK include the following:
- Mild discomfort may be present for 1 to 3 days following the PRK
procedure (typically minor irritation and watering).
- Somewhat longer time is needed to best uncorrected vision compared with
radial keratotomy or LASIK procedures.
What is LASEK?
LASEK (an abbreviation for Laser-Assisted Subepithelial Keratectomy) is a
modification of PRK. It uses 20 percent ethanol to loosen the skin layer of the
eye, which is then peeled back to perform the laser treatment. The skin layer is
then placed back over the cornea to accelerate healing and minimize the
discomfort of PRK. Some surgeons do not feel that LASEK offers an advantage over PRK.
What is LASIK?
LASIK is an abbreviation for Laser-Assisted In Situ Keratomileusis; it is also
nontechnically referred to as "Flap 'n Zap.". An instrument called a
microkeratome or the femtosecond laser produces a thin flap on the surface of
the cornea that remains attached to the surface by a hinge. The flap is folded
back and the excimer laser correction is applied beneath the flap; the flap is
then returned to its original position. The flap adheres without sutures (stitches).
LASIK can be used to correct myopia from 0.5 to greater than 10
diopters and farsightedness from 0.5 to greater than 4 diopters.
What are the advantages of LASIK?
The advantages of LASIK include the following:
- There is faster visual recovery compared with PRK-- typically a few days
to a few weeks.
- Adjustments can often be made by lifting the flap for up to 1 to 2 years
following the initial procedure. The flap is lifted and additional laser is
applied beneath the original flap prior to repositioning the flap.
- The procedure has the ability to correct levels of myopia greater than 7
diopters, with more stability of the correction long-term.
What are the disadvantages of LASIK?
The disadvantages of LASIK include the following:
- It is expensive — typically $300 per eye or more compared with other methods.
- It is technically more complex. Problems may occur with an irregular cut
by the microkeratome, producing an irregular flap that can permanently
- It is more likely to cause a loss of best vision that can be seen with
or without glasses at 1 year after surgery.
- It cannot be performed on corneas that are too thin or that have
epithelial basement membrane dystrophy.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 11/24/2009...#4651