How The Eye Works
To better understand LASIK and how the microkeratome and excimer
laser can be used to correct
myopia, hyperopia, and astigmatism, a short review of how the eye
works may be helpful.
When light enters the eye, it is bent by a clear, strong tissue
called the cornea. The cornea, in effect,
acts like a lens to focus incoming light onto the retina.
A person's vision is adversely affected when there is a problem with
the refraction of light entering
the eye. Myopia, hyperopia and astigmatism are three common types of
refraction problems.
In myopia or nearsightedness, light entering the eye does not focus
on the retina as it should, but
instead focuses at a point in front of the retina. Myopia is
frequently caused either by an eye that is
too long, or by excessive curvature of the cornea. The result of
myopia is that objects that are far
away appear blurry, although objects that are "near" to the viewer
can be seen in focus.
In astigmatism, the problem is not the length of the eye, but the
fact that the cornea has two
different curvatures and is shaped more like a football or
basketball. This results in distorted vision.
Often, people who have myopia also suffer from astigmatism.
In hyperopia or farsightedness, the image focuses beyond the retina.
Hyperopia or farsightedness is
frequently caused by an eye that iis too short or by excessive
flattening of the cornea. The result of
hyperopia is that objects that are far away and close up appear
blurry- depending on the level of
farsightedness.
The Lasik Procedure:
If you desire to have LASIK performed on one or both of your eyes,
you must thoroughly understand
the following:
During the LASIK procedure, you will be permitted to wear your
regular clothes. A companion should
accompany you to the laser center. You will not be given a general
anesthetic, but may receive an oral medication to help you relax. The other medication that you
will receive before and during the procedure are eye drops. (Anesthetic, antibiotic, steroid and/or non-
steroidal, anti-inflammatory
medications may be used as, as appropriate.) While allergic
reactions to these medications are rare,
please advise your doctor, and your surgeon, of any allergies you may
have. You will be able to ask
questions and talk to your doctor during the procedure.
In the laser room, you will be seated in a patient chair similar to
that in a dentist's office. At this
point, the laser's computer will already have been programmed with
your prescribed correction. The
chair will be adjusted to align your eye with the laser system and
the operating microscope. This
takes about five (5) minutes.
The skin around the eye to be treated will be cleansed with iodine
prep and your other eye will be
loosely tapes closed.
An instrument called an eyelid speculum will be placed between your
upper and lower eyelids to
prevent you from blinking.
Next, your surgeon will place the suction ring on your eye and the
suction will be turned on. It is
necessary to raise the pressure within your eye to approximately 65-
mm HG (mercury) or greater for
the automated corneal shaper to function properly. Once the suction
has been turned on, your
vision will temporarily dim. This is normal, indicating adequate
suction has been achieved, and
should last 1 to 5 minutes or until the suction is turned off.
If for any reason the proper amount of suction cannot be obtained,
your surgery may have to be
rescheduled. Once it has been assured that the adequate amount of
suction has been achieved, the
automated corneal shaper will be placed in the suction ring, passed
across the cornea, and reversed.
The suction will be turned off and the automated corneal shaper
removed from the suction ring. The
chair will be positioned under the excimer laser and the corneal flap
will be folded back to expose
the area of the cornea (stroma) to be treated with the excimer laser.
Next, your surgeon will ask you to stare at a red light overhead.
(Occasionally, the red light may
become difficult to see as the procedure progresses.) Your surgeon
will activate the excimer laser
and begin reshaping your cornea. While the laser is in use, you will
be asked to keep your eye as still
as possible. However, a small amount of eye movement will not affect
the outcome of the procedure.
Total laser time for most patients is about 60 seconds per eye. Your
surgeon will tell you how you
are doing throughout the procedure.
