Anti-reflective (AR) coating is commonly
seen on an eye care professional’s glasses, but not seen
as often on the lenses of their patients. According to the
Vision Council, only 28.5% of eyewear dispensed in the
United States in 2009 had AR coating on the lenses. This is
far behind the foreign market rate of 50 to 99% penetration.
Why is this? Common reasons may be the ECP is wary of the
new coatings due to past failure rates of AR coatings, an
incomplete understanding of the way AR works and the
benefits it provides, or they are unsure how to present the
product to the patient in an effective manner.
What is Anti-reflective Coating?
Anti-reflective (AR) coating is a series
of layers that is applied to the back and front surface of a
lens, or just the back if the lens is polarized, to help
reduce the amount of reflections on the lens surface and to
increase the amount of light passing through the lens.
Consisting of metal oxides, each layer is a thin film that
is designed to block a specific wavelength of light. The
more layers of film applied on the lens, the more
wavelengths that are blocked. AR works by the destructive
interference principle. The principle causes the light that
reflects from the inner and outer surfaces of each film
layer to become opposite of each other and thereby cancel
out.
How Does AR Coating Work?
AR coatings work by utilizing the light
phenomenon of wave interference. Wave interference occurs
when two light waves meet while traveling along the same
medium. There are two types of interference: constructive
interference and destructive interference.
Constructive interference occurs at the
location where the two light waves have a displacement in
the same direction. The two waves are either peaking or
falling at the same place causing the wave pulse to be
greater than each wave pulse on its own. The result is
greater reflection on the lens medium.
Destructive interference is the opposite.
It occurs when the two waves of light displace in opposite
directions. By achieving complete amplitude while at
opposites, the two light pulses completely destroy each
other.
Coatings of Today
Gone are the days of single layer AR
coatings that craze, scratch or smudge easily. Today’s
premium AR coatings have extra hard coatings that increase
its scratch resistance, as well as oleophobic, hydrophobic
and antistatic layers that help repel oil, water, and dust.
Not only do these layers decrease the amount of smears,
debris and dirt that stick to the lens, but they also make
the lenses easier to clean and thereby reduce surface
scratches from excessive cleaning.
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Oleophobic layers are especially
important with the multilayer coatings because the more
effective the coating, the more likely it is to show
smudges.
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Hydrophobic layers are thin layers of
silicone that are placed on top of the AR. It provides a
smooth surface that decreases the wetting angle of the lens.
The result is that liquids form small beads and can be
easily removed from the lens.
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When oleophobic and hydrophobic layers
are used together, they create a seal that acts as a
secondary scratch coat.
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Anti-static or Electro Magnetic
Interference (EMI) layers are placed on the lens to prevent
static build up. By reducing static on the lens, airborne
particles are a lot less likely to be attracted to the lens
and adhere to it.
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Premium AR coatings are actually
bonded to the lens surface, becoming one with the lens. This
decreases the likelihood of crazing that was a problem with
earlier generations of AR coatings.
Reaping the Benefits
Now, how does all this scientific data
actually help the patient? Well, AR allows 6.5% more light
to enter the eye for a standard CR-39 lens. For lenses with
a higher index of refraction, the AR would increase the
amount of light entering the eye by an even larger margin.
The result is clearer, sharper vision and reduced eyestrain,
which would benefit everyone, however in some situations,
the benefits are more noticeable.
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Occupational - Florescent lighting,
computers, cash registers and such, all cause an increase of
reflections in the workplace. This increase in reflections
causes eyestrain, headaches, fatigue and a decrease in work
productivity.
-
Night driving- External reflections
are a major problem when it comes to driving safely at
night. The reflections from oncoming headlights,
streetlamps, and the road can cause distractions and
discomfort to the driver. Internal reflections can cause
ghost images and result in a decrease in reaction time.
Peripheral vision is also increased with the utilization of
AR coatings.
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Sunwear- The annoying image of your
own eye reflected onto the back of the lens, as well as
distracting mirror effect of a dark lens on the back
surface, is eliminated by a back surface AR coat. Be sure
not to place AR on the front surface of a polarized lens
because it affects the polarization process and can reduce
the darkness of the polarized lens by as much as 8%. This
may not be desirable to some.
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Cosmetic- Shakespeare once said, “The
eyes are the window to the soul.” If reflections are
inhibiting eye contact and eye visibility, much can be lost.
AR coating enhances not only the appearance of the patient
but can increase the effectiveness of communication by
enabling better eye contact.
Recommending AR to the Patient
Although some surveys show that 60% of
patients would purchase AR coated lenses, only about 25% of
them do. It is up to the ECP to bridge this gap. The easiest
way to prove the benefit of AR coating is to demonstrate it.
With this in mind, everyone in the dispensary should be
wearing the product. It is hard to tell a patient that the
product will benefit them if the ECP doesn’t believe in
the product enough to wear it themselves.
Also, seeing is believing when it comes
to a product, so be sure that there are multiple types of AR
displays available in the practice. These displays should
show a specific benefit of the product. Very effective types
of displays include:
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The doughnut. The doughnut is a plano
lens with AR coating applied just to the center. When placed
against a dark background, it is very easy to see the
difference in the amount of light reflected between the
coated and uncoated portions.
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Glasses with a coated lens and a non
coated lens. This display is very effective for the fashion
conscious consumer because it really highlights the cosmetic
benefits to the patient, so be sure to place it in a stylish
frame. With this display, the patient can see how the
coating will actually look when being worn.
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An oleophobic/hydrophobic lens and a
permanent marker. Patients are familiar with permanent
markers so they are impressed when the ink of the marker
beads up on the coating and is easily wiped off without
leaving a mark.
A word of caution, although everyone can
benefit from AR coated lenses, AR coating does not work well
under certain environmental conditions. If a patient works
in an extremely dusty environment, it would probably benefit
them to buy a second pair of occupational glasses without AR
coating applied to the lenses. Also, be sure to explain
proper care and cleaning, as detailed by the manufacturer,
to the patient so that he or she can get the longest
possible life out of the lenses.
AR coatings are the icing on the cake
when it comes to lenses. They enable the wearer to see
things clearer, reduce eyestrain, increase productivity as
well as participate in activities more safely. With all
these benefits, it is important to recommend AR to every
patient. By believing in the product and showing the
benefit, the ECP can provide the best to the patient.
