Reproduced with permission of Lenses & Technology, Jobson Publishing LLC, copyright 1999.
Creating Patient-Pleasing Eyewear - by Palmer R. Cook, OD
Whether you know it or not, if you start with a lens prescription and a patient, and place an
order for finished eyewear, you are not just an “ophthalmic pharmacist,” you are an eyewear
designer! Successful eyewear designers- you included- strive to convert the ‘scrip the doc has
written into eyewear that meets four important needs for your patients. It allows them to see
well, it makes them look good, it’s comfortable, and the value perceived by the patient is equal
to or greater than the cost of the new eyewear. Fortunately we have lots of great ophthalmic
technology which can yield all of these intended patient pleasing benefits.
There’s More To It Than TechnologyIn designing eyewear you should consider more than just Rx, eyesize, bridge size, pd, and the
many technological options available today. It’s also important to consider Pupil Size, Previous
Eyewear History, and Patient Expectations. These areas are often overlooked, yet they can
yield very helpful information.
+Larger pupil size means a relatively decreased depth of field and possibly less tolerance to
marginal astigmatism and peripheral power gain. Lean toward a smaller eyesize, in trifocals to
deeper intermediate, and, in PAL’s, a harder lens design.
+Knowing the patient’s previous experience with eyewear is often helpful. “Have you ever had a
pair of glasses you couldn’t wear?” can be a wonderfully revealing question. A patient with a
history of not being satisfied with his or her last one, two, or three sets of spectacles is an odds
on favorite for having problems with yet another set. Perhaps medication, a physical problem
such as a fluctuating blood sugar level, or an unequal half pd, has been overlooked. This
important pre-design question can alert you to the presence of an easy-to-miss complicating
factor and help you avoid tons of trouble for everyone.
+Knowing the size, lens material, and other particulars of the previous eyewear will help you
predict what changes will be apparent when the new eyewear is dispensed. Patients generally
don’t appreciate paying for “new and improved” unless the thickness, weight, appearance, or
lens performance is perceptibly different from their previous eyewear.
+Not all eyewear options can be combined with success so look before you leap, and think
before you speak or you may generate patient expectations that cannot be met. A good
example could be the new atoric lenses which decrease peripheral aberrations in both major
meridians. These lenses improve ‘away from center’ vision for patients with astigmatism, but
they are not yet available in every lens material or style. Your patient’s confidence may suffer if
you have to call with a “Well, we just can’t quite have your glasses made the way we had
decided” statement.
+Patients naturally have expectations about the eyewear they have ordered. It is advisable to
demonstrate options such as tints, antireflection treatment, and aspheric curvature at the time of
ordering the new eyewear and again at the dispensing. For example, the patient’s new aspheric
lenses may be a lot flatter, optically speaking, but, especially in a small eyewire, the difference
may not be easily perceived unless the difference is demonstrated with a lens clock at the
dispensing table.
There are no absolute guidelines as to when to use some of the new technology options
except in the more extreme situations. In borderline situations, it is best to have an idea of what
the patient expects, is sensitive to, and can comfortably tolerate. For example, switching to a
high index, low specific gravity material for a mid-range Rx in a small eyewire may not save
enough weight to be significant. On the other hand, if your patient is highly sensitive, with a
pencil thin nose and paper thin skin, even fractions of an ounce in weight reduction can be
important and greatly appreciated.
Never Overlook Key FactorsThere are five key factors which should be considered when deciding which options to include
in a patient’s new eyewear. As an eyewear designer, you need to be sensitive to all of these
factors. If you aren’t, you can bet your patients and their families and friends will be sensitive to
them, especially and unfortunately, after the eyewear has been dispensed. These factors are:
APPEARANCE
In the minds of the public, “strong” lenses mean weak eyes and call attention to a perceived
physical deficiency. For hyperopes “strong” means thick lenses that bulge forward from the
spectacle frame causing the eyes to be magnified and glassy in appearance. For myopes,
“strong” means beady, minified eyes trapped in concentric bulls eye rings of internally reflected
light. These strong minus lenses also have thick edges that occasion sideways glances from
friends, relatives, and casual passersby.
Thickness- Excessive thickness is the primary cause for an undeservedly “strong” appearance.
Five ways of decreasing thickness for both myopes and hyperopes are:
+Achieve “O” decentration (i.e. the frame p.d. equals the patient’s pd). The frame pd is
determined by adding the eyesize to the bridge size. A 48-20 frame fit on a patient with a 68 pd
eliminates the need to add to lens thickness to compensate for decentration.
+Decrease the eyesize. This decreases the edge thickness for myopes and the center
thickness for hyperopes. Caution: If you decrease the eyesize and finish a plus lens from a
large, finished blank, you will end up with excessive edge and center thickness. The solution is
to have your lab surface the lenses so that you have a minimal finished edge thickness.
+Use and aspheric design. Flatter peripheral curves tend to reduce edge thickness.
+Increase the index. Higher index lenses have more light bending muscle and therefore don’t
have to be curved as much to achieve the needed prescription. There’s no doubt about it, flatter
curves do mean thinner lenses.
+Use polycarbonate, which permits safe, ultrathin centers. Reducing the center thickness of a
lens from 2.0 to 1.5 millimeters means that every point on the lens, including the edge, will be a
half millimeter thinner – affording both an improvement in appearance and a savings in weight.
Part of the art of achieving a good lens design lies in the way you mix these five ways of
thinning. The patient’s facial characteristics, prescription, and vocation and avocations are the
primary factors which determine which of these factors can be used to good and safe effect.
Facial Inset- High myopes have a facial inset problem that optically indents the portion of their
head that is seen through their glasses. This facial inset problem is a minification issue that will
not change with index changes or asphericity. Using a smaller “A” measurement and a frame
with wider eyewires makes facial inset less noticeable. Savvy dispensers often use frames with
turnback endpieces to allow a smaller eyewire to look wide enough in these situations.
Turnback endpieces extend laterally from the eyewire before turning back toward the ear.
Anti-Reflective Lenses- Patients who wear low power lenses are prone to problems with ghost
images. The lower the power, the worse the problem. Patients under one diopter of power are
the most affected. The single most effective approach for this problem is to use antireflective
lenses, and you should be proactive, specifying the antireflective lenses initially, rather than
waiting for the patient to complain. The most troubled patient with this will be the presbyope
with a low distance Rx having their first experience with spectacles. Watch out!
Antireflection coating should always be considered when using higher index lenses.
Reflections detract from appearance, and reflections may be as much as 30% or more intense
when high index material is used. This is because more light “splashes back” from high index
lenses due to their greater power to slow light compared to a lower index lens. For hard resin,
at index 1.49, the reflectance is about 4%. Polycarbonate, at index 1.58, reflects about 5.15%
of incident light, or about 28% more than hard resin. Using antireflection coating not only
improves lens performance and increases light transmission for the patient, it also improves
appearance by making the light reflected from the lenses less bright!
ABERRATIONS
All ophthalmic lenses perform well when the line of sight passes only through the optical
center, but when the line of sight deviates, passing through the peripheral portion of the lens the
effective power of the lens changes and unwanted astigmatic power changes occur – even in
spherical lenses. These effects and other unwanted optical distortions are called aberrations. If
only we had but one eye, immobile and fixed firmly in the center of our face, and two noses to
support the weight of eyewear! Alas, the basic human design incorporates two eyes that are
constantly roving about. (Just visit your local singles bar on a Friday or Saturday night if you
doubt it.)
Since it is difficult to train patients to use only their neck muscles as they change their
direction of gaze and since the neck muscles are unrelated to convergence or divergence, we
must design lenses that give the best possible performance away from the center – reduced
aberration lenses.
Corrected Curve & Aspheric- Some peripheral aberrations, particularly marginal astigmatism
and curvature of field, are reduced in ophthalmic lenses through “corrected curve” or more
recently developed aspheric designs. Aspheric lenses not only decrease peripheral aberrations,
their flatter curves give a less strong appearance, especially in larger eyesizes. Manufacturers
of high index materials recommend the aspheric lens curvatures that minimize peripheral lens
aberrations. Increasing these curvatures beyond manufacturers’ recommendations for better
lash relief, or decreasing them for a “less bulgy” appearance is not a good idea.
Chromatic Aberration & Abbe- Chromatic aberration, or color dispersion, is the other aberration
over which you have some control. Abbe numbers are used to indicate how much chromatic
aberration is present in the various lens materials. These numbers range from about 32 to 60,
with the higher numbers indicating less chromatic aberration. Patients in the mid-range
prescriptions are probably more sensitive to chromatic aberration than either low or high Rx
patients. Low power lenses just don’t separate the colors far enough for chromatic aberration to
be a problem.
Patients wearing high power lenses tend to stay near their lens centers simply because they
see better if they do. As a result they may be less annoyed by chromatic aberration since it is
always less bothersome when looking through the optical center. Many high Rx patients have
also learned the virtue of tolerance by experience with their high power lenses. This tolerance
helps them ignore increased chromatic aberration, especially if their new eyewear has offsetting
virtues such as lighter weight or increased break resistance.
Prism Prescriptions- Patients with prism prescriptions in all power ranges will be less tolerant of
increased chromatic aberration than patients with non-prism Rx’s in the same power ranges.
Lower their Abbe with caution. Patients with low refractive corrections who require prism
prescriptions, usually pediatric patients, will have more problems with reflections and “ghost
images.” They should have antireflective lenses.
It is important not to decenter aspheric lenses to achieve a prismatic correction. Patients who
require both a prismatic correction and an aspheric design must have ground in rather than
decentered prism. Decentering an aspheric lens to achieve a prism effect will cause a
prescription power error for the patient.
ADAPTION
The human body is marvelously adaptable. Witness the lips stretched with metal plates,
necks elongated with brass rings, and other body parts permanently and successfully deformed
in other cultures, and the spinal misalignments of women in our own culture who regularly wear
high heels. Since I have no experience adapting to high heels, much less lip plates and neck
stretching rings, I can’t make a first hand comparison, but it is almost axiomatic that ophthalmic
lenses of the correct power and of any reasonable design will be adapted to within 7 to 10 days
of constant wear. Unfortunately, it is a rare dispenser who cannot tell at least a few grim and
painful tales of “adaptation” problems.
The root cause of many of these horror stories lies in the patient’s fear that one, the problem
will persist, and two, there is no ultimate benefit associated with adapting to the new lens design
or material. True adaptation problems related to using new ophthalmic technology of index are
generally only mild to moderate. If a high index material or an aspheric is used for better
comfrot and appearance, patients should be motivated, without unduly suggesting problems, to
wait out any initial optical adaptation period.
WEIGHT
Weight is a function of the volume of space that a lens occupies and the specific gravity of the
material of which it is made. A strong lens can be made significantly lighter by using a material
with more light bending muscle, even if that material has a higher specific gravity, provided that
the lens volume is sufficiently decreased.
The kicker in this is: What is “significantly lighter?” How much more light bending muscle is
enough? AND, what does “sufficiently decreased volume” mean? From a practical standpoint
the lens designer must artfully mix the ingredients of light bending muscle, eyesize and bridge
size, cost, and patient tolerance considerations to achieve an acceptable weight factor.
Use the rule of 8’s & 2’s (below) to get an idea of how much weight will change with eyesize
changes. In the days of large eyesizes, a drop of 16% or 20% in lens weight was more likely to
be significant than the same percentage drop in today’s smaller eyesizes, so advice should be
tempered in this area.
COST/VALUE
Patients must perceive a value that is equal to or greater than the cost or they will experience
that disturbing phenomenon – buyer’s remorse. They must accurately perceive high value at
the time they order their eyewear, and that perception must persist as they receive and wear
their new eyewear.
When patients are asked to pay more for options and improvements they, rightfully, expect to
receive a perceptible benefit that justifies the cost. On the other hand, not using an option when
it is needed can also result in perceived value and buyer’s remorse problems. The trick is
knowing when to use those options.
Consider All Your Options- Using a higher index alone, without trying for “no decentration,”
reduced eyesize, and other design options may not get a “Wow!” reaction from the patient, and
can lead to buyer’s remorse problems- even though the higher index helps. The rule is:
Consider all available options. Patients invariably compare the new eyewear to the old. If they
are paying a premium for special options they will always have the expectation of receiving a
significant and perceptible benefit. Select carefully from all your lens design options to exceed
your patient’s expectations and achieve a patient-acceptable balance between benefits and
cost.
Dr. Cook is director of the Practice Support Division of Diversified Ophthalmics, Inc. in
Cincinnati, Ohio. He has served as a clinical instructor at both Ohio State University and
University of Houston College of Optometry, and has lectured extensively in the areas of
mechanical and ophthalmic optics.
The RULE of 8’s & 2’s:
1.) When you increase the size of the eyewire by one step (i.e. 2mm) the weight of the lens will
increase by about 8% if the lens is plano.
2.) If the lens has optical power (either plus or minus) you will have another 2% increase in
weight for every diopter when you increase the eyesize one step.
For example, a patient with a –8.00 Rx who jumps from a 50 to a 52 eyesize will have an
increase of about 24% in weight. There is an 8% increase (think of every lens as having a plano
carrier that increases 8% when the eyesize goes up 2mm) plus another 2% per diopter (2% x 8
= 16%). Adding the carrier’s 8% to the power’s 16% gives a 24% total increase in lens weight.
The Rule of 8’s and 2’s is an approximation that works for all lens materials as long as you
compare apples to apples. In other words a –8.00 that increases by 2mm in diameter will be
about 24% heavier whether it is made of crown, hard resin, or even high index. The Rule of 8’s
and 2’s doesn’t work in comparing lenses fabricated from different materials, but using it helps
educate patients to the need for a different material.
Reproduced with permission of Lenses & Technology, Jobson Publishing LLC, copyright 1999.