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Surgery for Presbyopia:
Even if you undergo LASIK or
PRK as a young person and
achieve perfect vision, you
still will develop a
condition called presbyopia
typically beginning between
the ages of 40 and 50.
Presbyopia is the inability
of the eye to focus at all
distances, usually noticed
when fine print starts to
blur.
Some eye doctors disagree
about what causes
presbyopia. Most believe
stiffening of the eye's lens
contributes to the
condition. Other theories
suggest that presbyopia
could also be related to
continued growth of the lens
or atrophy of the muscles
controlling the lens.
In the past, the usual
remedy was to wear reading
glasses or special
multifocal lenses (bifocal
or progressive) for
presbyopia. But in modern
times, surgical remedies for
presbyopia also are
available for qualified
candidates.
One of the first effective
surgical options for
presbyopia correction
involved producing what is
known as "monovision" during
LASIK. But other surgical
procedures such as
conductive keratoplasty or
CK (see below) also have
been approved by the FDA,
which gives eye surgeons
additional options for
correcting this common
vision problem.
Several other experimental
devices and procedures also
are under investigation, but
not yet FDA-approved. Here
is a rundown.
Monovision and LASIK
One way eyecare
professionals deal with
presbyopia is by producing
monovision. Normally, both
your eyes work together
equally when you look at an
object, to produce what's
called binocular vision.
However, you probably have a
dominant eye that your brain
tends to favor for
"sighting" (most
right-handed people are
right-eye dominant, for
example). Contact lens
fitters often take advantage
of this "one-eye dominance"
to produce monovision (think
of it as the opposite of
binocular vision) with the
contacts: they fit one eye
for distance vision
(typically the dominant eye)
and one for near vision.
Therefore, in monovision,
one eye does more work
(sighting) than the other.
If one of your eyes is set
for distance vision and the
other is set for near
vision, the distance eye
will do most of the work
when looking at objects in
the distance, and the near
vision eye will do most of
the work when looking at
objects close by.
Some LASIK surgeons will
produce monovision in their
presbyopic patients by
purposely leaving the
non-dominant eye slightly
nearsighted so that these
patients can see up close
without glasses (out of one
eye). Many are wary of the
technique because not
everyone can become
accustomed to the absence of
binocular vision. It's
better to try monovision
with contact lenses or trial
lenses in the doctor's
office first to be sure you
can adapt.
Monovision LASIK initially
was used off label, meaning
that it had not received
official FDA approval as an
approach to correcting
presbyopia. But in July
2007, the FDA announced
approval of the Advanced
Medical Optics (AMO) and
Visx CustomVue excimer laser
for performing the
monovision procedure.
Monovision and Conductive
Keratoplasty (CK)
Conductive keratoplasty uses
low-level, controlled
radio-frequency energy to
shrink collagen found in the
periphery of the cornea.
This steepens the central
cornea, in effect
lengthening a too-short
eyeball.
CK was FDA-approved in 2002
for the temporary reduction
of farsightedness, then
received approval in April
2004 for the temporary
improvement of near vision
in people with presbyopia.
This is another monovision
technique: CK is used to
help one eye see better up
close, while the other eye
is not touched. (If you are
already nearsighted, that
eye would wear a contact
lens to see at distance.)
Again, it's a good idea to
try monovision with contact
lenses or a trial lens in
the doctor's office before
going ahead with CK, to make
sure you'll adapt to it.
After the three-minute
procedure you'll likely
notice improvement, but it
can take a few weeks before
you reach the final level of
vision correction.
One attractive feature of CK
is that it is minimally
invasive. Some people
experience tearing,
foreign-body sensation,
and/or vision fluctuation,
but this is normally
temporary.
Laser Thermal Keratoplasty
(LTK)
In laser thermal
keratoplasty, mild laser
heat is used in a
three-second procedure to
shrink collagen in the
periphery of the cornea to
steepen the eye's surface
for correction of near
vision in farsightedness or
presbyopia. Results are
similar to those of CK (see
above).
Surgical Reversal of
Presbyopia (SRP)
with Scleral Expansion Bands
(SEBs)
Here, the surgeon inserts
four plastic segments made
out of polymethyl
methacrylate (PMMA) just
below the surface of the
sclera, which increases the
distance between the muscles
that focus the lens and the
lens itself. Researchers
think the extra distance
augments the tension of the
muscle, thus allowing it to
do a better job of focusing
the lens.
Results from early phase
clinical trials involved
five patients, all of whom
were able to read newspaper
print after scleral
expansion bands were
inserted. Modifications have
been made to the earlier
implants, and clinical
trials as of 2006 were
continuing. Overall, some
eyes that have received the
implants show improvement,
and some do not.
Presbyopia Research: Do
Tiny Bubbles Represent a
Cure?
No vision correction surgery
to-date has completely been
able to address these
focusing problems caused
when the eye's natural lens
grows rigid with aging.
But researchers at the
University of Michigan in
Ann Arbor reported in May
2006 that they have
developed a novel new
approach to correcting
presbyopia, which involves
using tiny bubbles to
precisely guide laser beams
as they restore flexibility
and focusing ability to the
eye's lens.
These tiny gas bubbles,
known as microscale bubbles,
first are created in the
area of the eye's natural
lens with laser pulses. Then
high frequency sound waves
(ultrasound) are used to
push the bubbles against
fibers making up the natural
lens. Ultrasound helps track
the movement and location of
these bubbles to guide laser
beams for precise placement
of energy designed to loosen
fibers and restore
pliability to the lens. The
technique has been perfected
in pigs' eyes.
"Part of the sound is
reflected, and from the
characteristic of the
reflection, you know where
the bubble is," said Matthew
O'Donnell, professor and
chair of the University of
Michigan Department of
Biomedical Research. "It
uses exactly the same
technology as ultrasound
imaging."
The team that created the
technology has been in
contact with several
companies interested in
commercial development,
O'Donnell said.
Artificial Lenses
(Refractive Lens Exchange or
RLE)
One currently available
option for presbyopia
correction involves removing
the eye's natural lens and
inserting an artificial one
in a procedure identical to
cataract surgery. While this
surgical procedure is not
FDA-approved specifically
for presbyopia correction,
it may be available off
label for qualified
candidates. The surgical
procedure, known as
refractive lens exchange
(RLE) or clear lens
extraction, is becoming more
popular because of the
recent availability of three
FDA-approved multifocal or
accommodative artificial
lenses capable of correcting
presbyopia.
Multifocal LASIK (Presby
LASIK)
Different zones in a
multifocal artificial lens
correct vision at near,
intermediate, and far
ranges. In an
investigational procedure
known as multifocal or
presby LASIK, zones are
established in a similar way
on the eye's clear front
surface (cornea) to correct
presbyopia. Multifocal
LASIK, also called presby
LASIK, is an investigational
procedure, which is not
FDA-approved. U.S. clinical
trials investigating the
effectiveness and safety of
the procedure currently are
being conducted.
Corneal Inlays
Currently in FDA clinical
trials, the ACI 7000
(AcuFocus and Bausch & Lomb)
is a corneal inlay inserted
just below your eye's
surface to provide vision
correction. This device
corrects presbyopia by using
principles similar to the
aperture or opening through
which light enters a camera
- the smaller the aperture,
the greater the range of
what you see in focus.
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