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PRK (photorefractive keratectomy), a refractive
eye surgery, is similar to LASIK in that both procedures employ
a computer-controlled excimer laser to reshape the cornea
(the front surface of the eye), in order to change its ability
to focus light on the retina of the affected eye.
PRK is characterized by a lengthier healing
process and more discomfort than LASIK. However, PRK requires
less instrumentation and avoids the creation of the flap and
its attendant risks.
Do
you Qualify for PRK?
PRK is not for everyone. There are
a few medical conditions that some people have that make them
poor candidates for this procedure. These conditions are rare
and can be detected during your pre-procedure examination
with what is called a Corneal Map. If a condition exists,
it is not wise to proceed and you will be told.
Additionally, a condition brought
on by the aging process, called presbyopia, cannot be treated.
Presbyopia is the loss of flexibility of your eye lens. This
causes many people to need reading glasses as they get older.
However, most people can have PRK. After (these conditions)
have been ruled out, there are few impediments to a successful
procedure.
PRK is approved in the United States for
the treatment of -1.00 to -7.00 diopters of myopia. With refinements
in software and improvements in ablation profiles, this may
increase to up to -10.00 diopters. However, the more tissue
removed, the more vigorous the healing response. Therefore,
it is more likely that there will be regression of effect
and haze and/or scarring.
If any of the following conditions apply
to you, then you are NOT a good candidate for PRK:
- Pregnancy.
- Unstable refractive error (your vision
has been changing over the past 12 months).
- Collagen/Vascular disease.
- Active ocular disease.
- Under 20 years of age.
- Pacemaker users.
Before
Your Surgery
There are some pre-operative procedures
that must be completed beforehand. If you are over 40, it
is important that you understand that PRK cannot correct the
need to wear glasses for reading (presbyopia).
The tests that must be completed before
your PRK procedure are:
- Eye History
& Examination to determine refractive error,
absence of eye disease and your expectations of the procedure.
- Corneal
Topography - The computerized videokeratography system
(EYESYS) projects a 16-ring (8 light and 8 dark rings) onto
the surface of the cornea. A CCD camera in the housing of
the corneascope captures the image of the projected rings.
A total of 5,760 points at 1 degree intervals of the cornea
are measured. A number of sophisticated computer programs
interpret the data and create a series of color graphic
displays. If needed, a hard copy can be obtained from a
color printer, Polaroid camera, or a 35mm slide. (a topographical
map of your eyeballs)
- Pachymetry
- A test performed to measure the corneal thickness
- Axial
length measurements
During
The Procedure
To make you comfortable
and the procedure pain-free, anesthetic drops will be placed
in the eye you are having treated. These are repeated a few
times over the period of one half hour to make sure your eye
is immobile. A speculum is gently placed on your eye to ensure
that your eye stays open while the surgeon performs the procedure.
There is no discomfort, since the drops placed in your eye
prior to the procedure will affect your eye until well after
the procedure is completed.
The technology varies from clinic to clinic.
Depending on the equipment, the surgeon will then place a
suction ring on your eye that will hold it steady for the
entire procedure. If the first technique is not used, other
methods of keeping your eye still will be employed (none of
them are painful) and you will be asked to stare straight
up at a light in the laser machine.
Some machines actually track and follow
the pupil. Rather than making cuts in the cornea, the PRK
procedure uses an excimer laser to shape an area 5 to 9 millimeters
in diameter on the surface of the eye. This process removes
only 5-10% of the thickness of the cornea for mild to moderate
myopia and up to 30% for extreme myopia - about the thickness
of 1 to 3 human hairs. The major advantage of this procedure
is that the integrity and the strength of the corneal dome
is retained.
PRK
vs. LASIK: Comparisons
| |
PRK |
LASIK |
| range
of correction |
low to moderate |
low to severe |
| wound
depth |
superficial |
20% deep |
| intraoperative
pain |
none |
none |
| post-op
medications |
3 months, possibly more |
1-2 weeks |
| functional
vision recovery |
3 to 5 days |
24 hours |
| visual
results fully recognized |
3 weeks to several months |
1 to 4 weeks |
| return
to work |
3 to 5 days |
1 day |
| risk
of complications |
low (more surgeon dependent) |
low (less surgeon dependent) |
| risk
of scarring in central cornea |
1-2 % |
< 1% |
After
Surgery
Some patients see a dramatic
improvement in their vision the first day. For others, vision
may be blurry and fluctuate for several weeks to several months.
Most patients return to normal activities in 1-3 days. Regular
follow-up visits are essential to monitor your progress and
ensure that you achieve the best results.
A series of follow-up examinations will
be scheduled to monitor your progress for up to a year. Normally
you will be seen a few days after correction, then for a series
of follow-up visits over the next twelve months.
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