Frequent Questions about Multifocal Lens
Implants
(24.09.2013)
(http://www.changcataract.com/los-altos/cataract-center/frequent-questions-about-multifocal-lens-implants.htm)
(www.karmayog.org)
By David F. Chang MD
Multifocal lens implants are an expensive but exciting
technology. They are designed to reduce your dependence on eyeglasses as
compared to if you had a standard single focus lens implant. When you are not
wearing glasses, a standard lens implant will provide your eye with optimum focus
set at one particular distance that does not change. You would then wear
glasses in order to change this focus (e.g., moving the focus farther away or
closer up).
How
does the multifocal work?
With bifocal eyeglasses, you look through the top part of
the lens for distance, and through the bottom area of the lens for near. The
multifocal lens implant is entirely different because the specially engineered
optic provides both a distance focus, and a near focus at all times. Your brain
will learn to automatically select the focus that is appropriate for the task
at hand. An analogy might be having background music playing in the room during
a conversation. Your brain might tune out one to listen to the other. There
is a brief learning curve for using this unique optical system. For example,
you will need to learn the optimal distance to hold reading material – the
so-called sweet spot. For this reason many patients report that their ability
to function without glasses continues to improve over time.
Will
this expensive technology eliminate the need for glasses?
Unfortunately, multifocal lens implants usually do not
entirely eliminate eyeglasses. There may always be situations where the print
or the images are simply too small or too far away to see without glasses. The
print quality and the amount of available light will make a difference. In
addition, your retina must be completely healthy to achieve the optimum
results.
Remember that how often an individual requires glasses
varies across a broad range of percentages. At one extreme is always (people
who must wear their glasses constantly = 100%); at the other end of the
continuum is never (some young individuals with perfect vision and a naturally
focusing lens never need glasses = 0%). Most of us are somewhere along this
continuum in between the two extremes. It is impossible to know in advance how
often you will need glasses after your multifocal lens implants. This depends
upon variables such as your retina, any remaining astigmatism, and how visually
demanding your everyday activities are. However, when compared to the standard
single-focus lens implant, the multifocal should put you much closer to the
desirable end of the spectrum discussed above. This is because the multifocal
lens provides you with focus at more than one distance (multifocal means more
than one single focal point).
Multifocal lens implants do offer the convenience of less
dependence on reading glasses compared to standard lens implants. People who
naturally see well in the distance often go without eyeglasses when outdoors or
around the house. However, when they need to see something up close even for
just a moment – they often have to put on reading glasses. Examples of common
momentary near tasks would be a looking at a cell phone, a photo, a menu, a
boarding pass, an envelope address, a handwritten note, or a price tag or
receipt. Having to frequently take their reading glasses on and off is
inconvenient for many people. Because of this, they might wear their reading glasses
around their neck, scatter multiple pairs around the house, or simply wear
bifocals all the time. Although they might still prefer eyeglasses for
prolonged reading, most people with multifocal lens implants can enjoy the
convenience of performing these simple near tasks without putting on reading
glasses.
Will
I see halos?
Depending upon the size of your pupils you may see halos,
which appear as a glow around lights at night. These halos are different from,
and much less problematic than those caused by cataracts. They relate to
viewing distant lights through both the near and far focusing zones of the
lens. They do not obscure the vision, but rather can create a distracting ghost
image. Fortunately, these halos become less noticeable and distracting over
time as the brain learns to selectively ignore them through a process called
neuroadaptation. This is the same process that allows us to ignore background
noise, such as traffic sounds or an air conditioning fan. Another analogy would
be the temporary distraction of wearing earrings, jewelry, or a seatbelt for
the first time. As these sensations become more familiar over time, we become
less aware of them. How quickly this adjustment occurs varies for different
individuals. However, experience has shown that neuroadaptation is a gradual
process and that suppression of the nighttime ghost images continues to improve
throughout the course of the first year.
Even a standard lens implant can produce some halos at
night, but they are more evident with a multifocal lens implant. This is
because the pupil dilates in the dark allowing more light to enter the interior
of the eyeball and to scatter off of the peripheral parts of the lens implant.
Halos are always very noticeable during the first 24 hours after surgery when
your pupil is still dilated. Do not be alarmed by this temporary artificial
situation. The first generation multifocal lens implant that was introduced in
the late 1990s produced very prominent halos that were difficult for many
patients to adapt to. The newest multifocal lenses have been successfully
re-engineered so as to significantly reduce the halo effect compared to the
earlier model.
Can
the multifocal lens be implanted in just one eye?
Yes, this is possible when the other eye already has a
standard implant, or when there is no cataract in the opposite eye. However,
the ability to see both far and near without glasses is better when you have a
multifocal lens in both eyes. With a multifocal lens implant in one eye, the
brain simply integrates all of the vision that you get with both eyes open. For
this reason, you shouldnt constantly compare one eye to the other. Some
individuals may take longer than others to adapt to this situation. With a
multifocal lens in one eye, you should still have more ability to see things
close up, as compared to if you had received a standard single-focus lens
implant.
Can
the multifocal lens be removed if I dont like it?
This is always possible but entails the risks of
additional surgery. However, there may be a rare individual for whom the halos
continue to be unacceptable, and who then elects to have the multifocal
replaced with a standard lens implant. One should not rush into this decision
because the ghost images nearly always improve over time. However, removal of
any lens implant generally becomes more difficult after 4 months.
Does
insurance cover the premium cost to upgrade to a multifocal?
Unfortunately it will not. Health insurance whether a
PPO, HMO, or Medicare – covers a cataract operation with a standard lens
implant when the cataract is bad enough to be considered medically necessary.
The additional fee to upgrade the lens implant to a multifocal is not covered,
because the added convenience of reducing your dependence on eyeglasses is not
considered medically necessary. We ask that you pay this premium
out-of-pocket fee in advance, because we will be ordering the multifocal lens
implant in your specific power for you.
Can
patients without cataracts have multifocal lens implants?
Many people are interested in surgical methods to reduce
their dependence upon eyeglasses and contact lenses. Laser eye surgery, such as
Lasik, is the most common way to correct nearsightedness if one is under the
age of 40. However, for patients over the age of 50, laser surgery by itself is
less advantageous. By this time of life, any method that corrects your distance
vision (including contact lenses, Lasik, or a standard lens implant) will not
work for reading up close without glasses. Another problem with laser eye
surgery, such as Lasik, is that it complicates any lens implant surgery that is
done later on for a cataract. Unfortunately, determination of the correct lens
implant power is very unpredictable in eyes that have had prior Lasik.
The multifocal lens implant is the only technology that
can allow a 50+ year-old eye to have focus both far and near without glasses.
For this reason, people over the age of 50 wearing strong prescription glasses
may elect to have multifocal lens implants in order to see much better without
glasses. However, with no cataract present, health insurance covers none of the
costs. Because the natural lens must still be removed before implanting a
multifocal lens, the procedure is performed in the same way as for cataract
surgery. Thus, patients electing to have lens implant surgery to reduce their
need for glasses will never have to worry about developing cataracts later on
in life.
Who
might need a Lasik enhancement after a multifocal lens implant?
Like contact lenses or eyeglasses, every artificial lens
implant model (both standard and multifocal) is manufactured in more than 60
different powers. As with prescription eyeglasses or contact lenses, it is
important to match the appropriate artificial lens implant power to your eye.
To prescribe the correct spectacle or contact lens power, we utilize trial and
error to preview various lens powers in front of your eye. When you are asked,
which is better, one or two? you are selecting the lens power that you see
best with. However, because the artificial lens implant is inserted inside the
eye, and only after your natural lens (cataract) has been removed, it is
impossible for you to preview or try out different powers before surgery. We
obviously cannot insert more than one lens implants and then let you select
which one gives you the best distance focus. Finally, once it is implanted, we
cannot easily exchange the lens implant the way we could with contact lenses or
eyeglasses.
Fortunately, the appropriate power of the lens implant
can be estimated using mathematical formulas that utilize preoperative
measurements of your eyes dimensions. Although the measurements are very
accurate, there are individual variables that prevent this process from being
100% perfect. One variable is the final precise position where the implant will
end up inside your eye. Astigmatism is a naturally occurring imperfection in
the optical shape of your cornea. Astigmatism is therefore not corrected by the
lens implant placed inside the eye and is another variable that may reduce your
ability to see without glasses. The entire process is accurate enough so that
most patients will see quite well without glasses in the distance (assuming that
was the target). However, it wont be perfect and you might choose to wear
glasses with a mild prescription for those times when a sharper distance focus
is required.
For a multifocal lens implant to work well, it is very
important for the selected lens power to match your individual eye. Despite
flawless surgery, some patients with multifocal lens implants are still not
able to see as well without glasses as they would like. If this is due to the
lens power being off, what can be done? One option is to wear glasses or
contact lenses. A theoretical solution might be to exchange the multifocal lens
implant for another with a different power. However, because of the risks
involved with removing a lens implant, it is usually safer to enhance or fine-tune
any residual prescription with an external Lasik procedure on the cornea
instead. Lasik can also correct any remaining astigmatism coming from your
cornea.
Every type of eye procedure intending to reduce a
persons need for eyeglasses may need to be enhanced with additional surgery.
For example, nearsighted people choosing to have laser eye surgery (e.g. Lasik)
may need a second treatment if the first one does not fully correct their
prescription. This unpredictability is understandable because we are not
machining plastic or metal, but are working instead with human tissue.
Likewise, it is possible that either the standard or
multifocal lens implant that has been selected may not adequately correct your
distance prescription. Depending upon how far off we are, laser enhancement can
be a good option. The odds that this would need to be done with a multifocal
lens are usually less than 10%. The chances are greater in patients with high
astigmatism or requiring very strong prescription glasses to begin with. The
need will also depend upon how much better one wants to see without glasses.
Because I specialize in lens implant and cataract surgery only, I would
collaborate with a local Lasik specialist, called a refractive surgeon, if this
need arose. However, because there would be an additional cost and procedure
involved, you should know about this possibility in advance before making your
decision to have a multifocal lens implant.
What
do you recommend I do?
Like cosmetic surgery, taking extra steps to reduce
spectacle dependence is a discretionary and personal decision. Because this
does not involve health advice or medical needs, the ultimate decision is
yours. Start by evaluating how strong your desire is to see as much as possible
without glasses. Every individual will value such convenience quite
differently. My role, as your ophthalmologist, is to explain your options to
you. To implant these special lenses, eye surgeons must be trained and
certified by the manufacturers. I have extensive experience with all types of
multifocal lens implants, and frequently lecture or write articles on this
subject. Many lens manufacturers have asked me to consult or to assist in
training other eye surgeons. Fortunately, your options are not limited by any lack
of experience on my part.
Summary
If you are a patient with cataracts, you are considering
surgery because your cataracts prevent you from seeing well with your
corrective eyeglasses. After cataract surgery you should be able to see well
for both far and near distances with your new eyeglasses (assuming no other eye
health problems). The decision about which type of artificial lens implant to
have will only affect your ability to see without eyeglasses following cataract
surgery. With both standard and multifocal lens implants, most people will see
reasonably well in the distance without any eyeglasses. However, multifocal
lens implants will provide the added convenience of being able to read many
things without glasses.
No current technology can eliminate glasses, and how well
you will perform with multifocal lens implants can vary because of individual
factors. Nevertheless, they are an excellent option for patients who already
need cataract surgery who want to decrease their reliance upon glasses. While
multifocal implants carry no guarantees, they should greatly improve the odds
that you will be able to read and see better overall without glasses.