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LASIK
& PRK
The cornea and lens combine to focus visual images on the
retina, in the back of the eye. When the overall shape of
the eye is incorrect or when the curvature of the cornea
is incorrect, the visual images are not in focus. The cornea
accounts for approximately two-thirds of the focusing power
of the eye. By surgically changing the corneal curvature,
the image can be placed clearly in focus on the retina with
most or all of the blur eliminated.
Laser In Situ Keratomileusis (LASIK) and the
older Photo-Refractive Keratectomy (PRK) are two surgical
techniques which utilize lasers to reshape or change the
curvature of the cornea.
LASIK
LASIK had its origins about thirty years ago and was originally
developed to treat patients who had very poor vision due
to corneal disease. It has now evolved into a successful
technique for correcting refractive errors. The current
procedure, done on an outpatient basis, involves both the
use of conventional and laser surgery to correct nearsightedness,
farsightedness and astigmatism. LASIK can correct a much
higher degree of nearsightedness, with or without astigmatism,
than any other refractive procedure, with excellent results.
Current data indicate that 99.7% of patients maintain best
corrected visual acuity of 20/20 or better.
The LASIK Procedure
In performing LASIK, eye drop anesthetic is used to numb
the eye. The surgeon then uses a special instrument called
a micro-keratome to cut into and behind a layer of the cornea.
A portion of the cornea is lifted back to create a flap
and expose the inner portions of corneal tissue. The eye
is then positioned under the excimer laser, which has been
computer programmed to remove microscopic amounts of the
internal corneal tissue. Removal of the tissue changes the
curvature of the cornea. Infrared tracking technology is
currently being used which allows the computer to adjust
the treatment for any tiny movements of the eye during the
laser treatment. This allows for more safe and accurate
outcomes.
If the patient is nearsighted, tissue closer to the central
part of the cornea is removed to decrease the curvature
and effectively flatten the cornea. If a patient is farsighted,
tissue in the peripheral part of the cornea is removed to
increase the curvature of the cornea. To correct for astigmatism,
selected tissue at certain angles is removed to ensure that
the cornea curves equally in all directions.
After the laser has been used, the flap is returned to its
original position. The corneal tissue has extraordinary
natural bonding qualities that allow effective healing without
the use of stitches.
Since only local anesthetic is used, patients remain awake
during the procedure. The entire procedure takes only a
few minutes. Improved vision is often possible on the day
following the surgery. After surgery, eye drops are prescribed,
and it is be necessary to wear protective eye goggles, like
sport goggles, at night for approximately one week.
Advantages of LASIK:
The advantages of LASIK include a much faster healing time
than other refractive surgical methods, rapid visual recovery,
less risk of scarring, less risk of corneal haze, and less
post-op discomfort. As a flap is created during LASIK surgery,
flap management is an additional consideration.
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Photo-Refractive
Keratectomy (PRK)
Photo-Refractive Keratectomy, or PRK, is another method
of surgically reshaping the cornea using the excimer laser.
The difference between LASIK and PRK is that for PRK, a
corneal flap is not created. That is, the outer layer of
the cornea remains in place and the laser removes tissue
directly from this outer layer. PRK is used for low to moderate
amounts of nearsightedness.
Just as in LASIK, the laser treatment
for PRK requires only a few minutes. But unlike LASIK, the
healing period takes longer, there is greater discomfort,
more medications are used for a longer period of time, and
the time to visual recovery is prolonged. The correction
for nearsightedness, farsightedness, and astigmatism is
the same as in LASIK. The majority of refraction surgeons
prefer to perform LASIK over PRK except in instances of
thinner than normal corneas or when there is a question
relating to optic nerve health.
Intra
Ocular Lenses (IOLs) for Refractive Surgery or Implantable
Contact Lens (ICL)
When the eye is unable to properly focus,
the result is blurry vision. One option to correct for this
is IOLs (Intra Ocular Lenses). IOLs have been used for many
years to replace the natural lens during cataract surgery.
IOLs for refractive surgery differ significantly from other
refractive methods in that they do not involve changing
the shape and/or structure of the cornea (the clear outer
layer of the eye). IOLs replace the natural lens (phakic
lens) of the eye and can correct for significant refractive
errors, which can greatly enhance vision.
Phakic IOLs are ideally suited for individuals who are poor
candidates for other refractive options, such as LASIK.
This includes those with high refractive errors, including
myopia greater than -10 diopters and hyperopia greater than
+4 diopters. In addition, phakic IOLs are also an excellent
choice for those with keratoconus, those who have thin corneas,
or for those who are no longer able to tolerate contact
lenses or eyeglasses.
The IOL Procedure
Inserting a phakic IOL is a nearly identical process to
the lens implantation portion of a cataract procedure. Before
surgery, an extensive set of eye tests are taken to determine
the proper power of the lens to be inserted. The actual
procedure is then performed through a small incision in
the cornea. In some cases, tiny foldable IOLs can be inserted
through a smaller incision (1/8 of an inch wide). Once inside
the eye, these lenses unfold into a full-sized IOL. The
advantage of the small incision approach is improved safety
and faster recovery of vision after surgery.
The Intra Ocular Lens is implanted between
the iris and the front surface of the human lens. IOLs are
made of the same plastic as certain types of contact lenses.
The procedure is typically performed with a general or topical
anesthetic.
Health Issues Associated with Phakic IOLs
As with any surgery, complications are rare but do exist.
The main drawback to IOLs is that, unlike other refractive
surgery options, the incision and procedure is performed
inside the eye (as opposed to on the surface). The nature
of this surgery carries heightened risks for internal eye
infection or damage. A consultation with your Ophthalmologist
or surgeon can address potential health complications.
Because the 'IOLs for refractive surgery'
procedure is a reversible process, it offers an advantage
over some other procedures. If the results are less than
optimal, the patient can choose to have the IOLs surgically
removed. IOLs typically last forever. Unlike other refractive
surgery options, IOLs do not weaken the strength or integrity
of the eye.
Intacs
Nearsightedness is an extremely
common condition in which the curvature of an individual's
cornea is too steep to properly focus light onto the retina.
Intacs (Intrastromal Corneal Ring Segments) are a safe,
easy, non-laser alternative for correcting mild nearsightedness.
Intacs are extremely thin, crescent-shaped plastic polymers
that, when implanted in the eye, restore the cornea to its
ideal curvature, resulting in clear, focused vision.
An initial consultation
with a refractive surgeon can determine whether or not a
patient is a good candidate. Intacs are ideally suited for
individuals with nearsightedness of -1.00 to -3.00 diopters
and no more than 1.00 diopter of astigmatism. (A diopter
is a measure of the power of eyeglasses or contact lenses).
Patients also need to have stable vision and generally healthy
eyes to qualify for Intacs.
Prior to the insertion of Intacs, a small
opening is made at the very edge of the cornea. Two crescent-shaped
pockets or tunnels are made on the periphery of the cornea,
outside the central optic zone (the area where the main
ocular functions occur). These pockets are created between
the layers of the cornea (known as the stroma), and the
Intacs are fitted inside. The thickness of the Intacs depends
on the amount of flattening needed -- the thicker the Intac,
the more flattening occurs. Once the Intacs have been fitted
inside the eyes, the small opening is closed up.
Intacs essentially reshape the cornea, allowing it to maintain
its proper curvature. Anesthetic eye drops numb the eye
to make the short procedure virtually pain-free. The procedure
lasts 15 to 30 minutes and is performed on an outpatient
basis.
Following surgery, many patients return home and rest for
the remainder of the day. Improved vision typically begins
to occur within the first 24 hours. Intacs are designed
to remain in the eye permanently, although they can be surgically
removed if the need arises. They are about as easy to detect
as a pair of contact lenses.
Orthokeratology
It is estimated that roughly 30% of the U.S.
population suffers from nearsightedness, or difficulty seeing
at a distance. Orthokeratology (also referred to as Ortho-K
or OK) is an older, essentially outdated method of temporarily
reshaping the cornea with a rigid contact lens. It is rarely
used today.
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