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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 of 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 images that are being focused behind the eye are
moved forward to the retina.
The official Food and Drug approved use of PRK is 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).
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:
- A low chance of complications when used for small visual acuity corrections.
- Is a highly accurate procedure for the correction of myopia up to 7 diopters. Approximately 80 percent 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 contact lenses.
What are the disadvantages of PRK?
The disadvantages of PRK include:
- 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.
What is LASIK?
LASIK (an abbreviation for Laser Assisted
In Situ Keratomileusis; 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 before returning the flap to its original position. The flap adheres
without sutures (stitches).
LASIK can be used to correct myopia from 1 to 10
diopters and farsightedness
from 1 to greater than 4 diopters.
What are the advantages of LASIK?
The advantages of LASIK include:
- Faster visual recovery compared with PRK-- typically a few days to a few weeks.
- Less of a chance that topical medications will be needed after surgery.
- Adjustments can 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
- Ability to correct levels of myopia greater than 7 diopters.
What are the disadvantages of LASIK?
The disadvantages of LASIK include:
- Expensive — typically $300 per eye or more compared with other methods.
- Technically more complex. Problems may occur with an irregular cut by
the microkeratome, producing an irregular flap that can permanently effect
vision.
- More likely to cause a loss of best vision that can be seen with or
without glasses at 1 year after surgery.
- Cannot be performed on corneas that are too thin or have epithelial
membrane dystrophy.
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