There is a new movement in the eye care profession today:
the knowledgeable (or “I think I am knowledgeable”)
patient.
They come into optical dispensaries with printouts
from websites, photographs and articles. The internet has
made tremendous amounts of information easily accessible to
the general public, but it is not always interpreted
accurately. Many patients now research the products they are
interested in by utilizing professional sites, social
networking sites and chat rooms to ask their friends, family
and co-workers about current products and services.
Informed consumers then come to the eye care
professional, who must be prepared to answer their questions
in an easy to understand, knowledgeable manner. It may also
be necessary to dispel any misinformation that the patient
may have. The following are some common questions that the
patient may have after their internet browsing.
What are the differences in the lens materials?
In the past, there was only one option in spectacle lens
materials: glass. Today, there is a whole new world of
possibilities available.
Plastic
Also called CR-39, plastic lenses are the basic lens
material used today. It has a high clarity level and works
well for lower prescription powers. It does not have an
inherent scratch resistance or ultraviolet protection, so
these coatings need to be added to the lens to make them
work well for the patient. It is heavier and less impact
resistant than some lenses, so it is not the first lens of
choice for higher prescriptions, children’s or sports
glasses, or drill mount frame styles.
Polycarbonate
Polycarbonate is the extremely safe, highest impact
resistant lens material available and has UV protection
built into the material itself. It is ideal for eyewear that
must have safety requirements such as safety glasses, sport
glasses and children’s glasses. It is thinner (center
thickness can go as low as 1.0mm due to its strength) than
glass and plastic materials and also lighter in weight.
An extremely soft material, it is hard coated by the
manufacturer to provide excellent scratch resistance. It is
not the best material for drill mounted frames, however. Due
to the softness of the material, the screws or posts in the
drill mount designs eventually wear the drill holes down,
causing the frame to loosen at the lens attachments. It also
has a low Abbe value. However, if the lens is fit properly
for most patients it is not a concern.
Trivex
The newest impact lens material to enter the market is
Trivex. Developed for the military in 2001 by PPG, Trivex is
the only lens material other than polycarbonate to pass the
High Velocity Impact Test, the FDA Impact Resistance Test at
1 mm center thickness and meet ANSI Z87.1 standards. Also
like polycarbonate, it is inherently ultraviolet protective.
It is here that the similarity to polycarbonate ends. This
material is thicker than polycarbonate, but it is slightly
lighter in weight than polycarbonate. It is also has a
higher Abbe value than polycarbonate so it has less
dispersion. One of Trivex most important attributes however,
is its tensile strength. Because of its high resistance to
cracking from drilling and stress, it is ideal for drill
mounting when you cannot use polycarbonate.
Hi-index
Hi-index is the high demand material in the optical
field. In order to truly understand the benefits of the
material, it is important to define index. In simple terms,
index is a measurement of how much light is slowed down by
the lens material. The higher the number, the more the light
is slowed down and therefore bent by the lens. What this
means to the eye care professional is, the higher the index,
the less material that is needed to bend the light to fill
the doctor’s prescription. For example, a -7.00D lens
ground on a 1.70 index material will be approximately 50
percent thinner than a -7.00D lens ground on a 1.50 index
material if all parameters are equal. When discussing
lenses, hi-index lenses are those with an index of 1.58 or
higher. However, remember that polycarbonate can have a
thinner center thickness which leads directly to thinner
edge thickness. A high index lens is not necessarily the
thinnest lens when all matters are considered.
What is an aspheric lens?
Many think an aspheric lens is a type of lens material.
Actually it is a lens design. A spherical lens has one large
curve on the front of the lens and then one or two curves
ground onto the back surface of the lens. Aspheric lenses on
the other hand, have multiple curves on the front surface of
the lens. These front curves are designed to have a gradual
power change from the center of the lens to the periphery.
The benefits of this lens type are that it gives a wider
field of view when one looks off to the side of the lens and
the lens is flatter. The result is a lens that fits closer
to the eye, is flatter and thinner, fits better in most
frames and reduces the magnification and minification of the
eye as well as the image formed on the retina.
What is AR coating and why do I need it?
AR, or anti-reflective coating, is a multilayer coating
that is applied to the surface of a lens to help ease eye
fatigue and eliminate most reflections. Now, the old AR
coatings used to scratch easily or get smudged or dirty
frequently. This is not the case with the newer, premium
coatings. These newer coats have an anti-static coating
which repels dust from the lens surface, as well as an
anti-smudge coating that causes fingerprints and water to
virtually disappear from the surface. It is beneficial to
anyone who wants the clearest vision possible, but
situations in which AR is especially beneficial are driving,
working, and times when minimizing the appearance of the
lens is especially important.
Improved Night Driving
-
AR improves the flow of light through a lens, thereby
increasing visual acuity. How this especially helps with
night driving is through the:
-
Elimination of ghost images
-
Reduction of the “rearview mirror effect”. This
occurs when the light from behind the driver reflects off
the patients lens back into the eye of the driver
-
Improved reaction time of the eye when adjusting back
to normal after glare from an oncoming vehicle
-
Improved peripheral vision
Enhanced Contrast
When light doesn’t enter the lens and through the eye
clearly, the quality of the image that reaches the eye is
not as sharp as one would like. The lack of contrast causes
blurring, double vision and eye fatigue. Because of this, AR
coating is especially important when one is:
-
Wearing advanced technology lenses such as hi-index or
aspheric lens designs
-
Working under artificial lighting
-
Driving for long periods of time
-
Working with computers
Cosmetic
Lenses have a windowpane reflective effect when not
coated with AR. Although it does not disturb the vision of
the wearer, it does cause others to not be able to see the
wearer’s eyes. This can be a hindrance to individuals who
work in sales, present themselves to the public, or are in
an occupation in which they have to do a lot of public
speaking. It can also be a problem for those who just want
to look their best. AR coating helps with all these issues.
Are prescription sunglasses really worth it?
There are two main options when it comes to sunglasses.
There are tinted lenses and polarized lenses. Tints,
although an effective option in sports eyewear, are not as
efficient as polarized lenses. Tinting only makes the lens
darker, thereby blocking the amount of usable light entering
the eye while allowing glare to pass through. Polarization
on the other hand, acts as a filter. Polarization is a film
that is applied in the lens and acts like a Venetian blind,
blocking reflected horizontal light that causes harmful
glare. Polarized lenses:
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Enhance contrast
-
Eliminate dangerous glare
-
Reduce eyestrain
-
Increase depth perception, particularly around water
-
Enhance visual clarity
-
Reduce visual fatigue especially when driving
By wearing a properly fit pair of prescription
sunglasses, incidences of sporting accidents and car wrecks
can be reduced greatly.
Aren’t all progressives the same?
There are over 200 different progressives on the market
and that can create some confusion for both the patient and
the ECP. One way to help is to create a Good, Better, Best
chart for the patients so that an informed decision can be
made. Best should be presented first with the patient’s
lifestyle, prescription, frame style and material needs
taken into account.
Conclusion
Dealing with an informed patient can be challenging as
well as rewarding. It is the eye care professional’s
opportunity to expand his or her knowledge as well as help
patients find the best fit for their needs. The educated ECP
is the most important resource any patient can have no
matter how much time they spend on the internet.
