By Barry Santini, ABOM
Photographs by NED MATURA; Drivewear Lenses courtesy of Younger Optics. Frame: Persol/Luxottica
Although the Departments of Motor
Vehicles (DMVs) in each of the 50 states
has a different protocol for driver testing,
licensure and re-registration, they all share
one thing in common: a person’s vision
must meet a minimum standard of acuity.
This fact alone should persuade every
vision professional (whether optician,
optometrist, ophthalmologist or support
staff) that emphasizing the importance of
having the sharpest vision possible when
driving is not only good for each client, it’s
also good for society as a whole. Can you
name another activity where less-thanoptimal
vision poses such a potential danger
for both an individual and others
around them? Driving with sub-optimal
acuity can result in reduced depth perception,
low-level contrast discrimination,
accuracy in judging distances and negatively
impact traffic signal recognition. All
of these deficiencies affect a driver’s reaction
time and will therefore significantly
increase chances for an accident. And
while having sharp vision will not guarantee
avoiding an accident, driving without
it will certainly increase your odds.
VISION CONSIDERATIONS
When considering how to optimize a driver’s
vision, we should first evaluate the visual conditions
affecting driving. The most important
factors that influence these visual conditions
are the time of day (daytime, dusk or night
time) and the driver’s field-of-view.
DAYTIME DRIVING
Daytime driving is generally done under
photopic conditions. Photopic conditions
mean your pupils will constrict to 1.5 to
3mm in response to the elevated lumen levels.
However, smaller pupils can effectively
mask focus error because the rays limited by
these diameters tend to produce a sharp
image. As a result, many clients may have
prescriptions that indicate a small correction
is needed, even though the client may not
complain of vision problems when driving.
This is why a proper refraction is generally
performed in a darkened room (where the
pupil can open up to at least 5mm). These
conditions will reveal any lack of optimal
focus. With this in mind, it is obvious that
most motor vehicle acuity tests are not done
in appropriate conditions. The current testing
environment in most DMV offices features
both bright lighting and reduced testing
distances. These two testing parameters
further compromise the reduced acuity
thresholds employed by the DMVs. (It is
also ironic many states have, or are considering
laws that mandate pre-schooler
screening standards—along with subsequent
doctor referral—that utilize acuity
thresholds far more stringent than our
DMVs currently allow.)
Besides the basics of full prescription correction,
daytime drivers must contend with
the direct glare of the sun. When recommending
sunglasses, the proper selection of
tints and densities should be reviewed and
determined with each client. There are various
gender considerations that can influence
the choice of lens color (also know as
“hue”). While we’re familiar with the spectral
differences between the primary sunwear
color families of gray, brown and
green, it is also important to note there are
some differences between male and female
color vision that will influence their preference
of lens hue. In general, most men’s
color vision is red-sensitive and often prefer
a neutral-transmittance lens such as gray. On
the other hand, most women are red-deficient,
and often find a gray tint “flat” or dull,
while a brown-based tint appears to provide
more “natural” vision. These gender guidelines
are by no means universal. Individual
demonstrations are recommended for each
client. In addition, people will often become
accustomed to a particular tint during years
of use (visual habit). Demonstrating all the
primary and secondary sun tints (rose, for
example) is the only way to discover the
optimal choices for your client.
Photochromic lenses are a popular lens
option today. But for almost all types, photochromic
lenses do not work optimally for
driving. The UV rays that change the lens
from light to dark are blocked by a car’s roof
and window glass.
An exception is the new Drivewear lens
from Younger Optics. Developed in conjunction
with Transitions Optical, Drivewear
lenses are polarized photochromic lenses that
are activated by both UV and visible light.
Drivewear lenses can darken in a car, with a
response proportional to the brightness levels
encountered. Along with their photochromic
quality, Drivewear lenses also feature
optimized hue-changing qualities that
further enhance their glare reduction.
Daytime drivers can also encounter the
debilitating glare effects of reflected light.
Whether glare reflections originate off window
glass, the dashboard or the road surface,
polarizing lenses are the ideal solution.
Through selectively blocking of reflections
from horizontal surfaces, polarizing lenses
deliver improved contrast sensitivity, and
thereby, allow drivers to more quickly see a
child, bicycle, pedestrian or car lurking in
the shadows of trees or buildings.
DUSK AND NIGHT TIME
The most important difference between
daytime and dusk or night time driving is a
reduction in contrast. Lower lumen levels
result in mesoscopic or scotopic conditions,
and encourage your pupil to dilate between
4mm and 7mm. At these diameters, any
lack of optimal eye focus will no longer be
camouflaged. These are the conditions that
will often be accompanied by some sort of
complaint from your client. If their correction
is not fully up to par, this is the environment
where it will show. Even if their
last refraction concluded with a “no correction
change needed,” drivers often complain
about a lack of visual comfort and
confidence during dusk and night time
conditions. These evening considerations
are really completely different from daytime.
Unfortunately, our current refraction
protocol does not routinely include optimizing
driver vision for dusk and night.
NIGHT MYOPIA—
THE “HIDDEN” NEARSIGHTEDNESS
Although still not yet fully understood,
night myopia significantly influences vision
sharpness and contrast discrimination. Primarily
evolutionary in origin, night myopia
is defined as the eye’s tendency to adopt a
nearsighted focus at larger pupil openings
(6mm to 8mm), and under low levels of
illumination. It is postulated that evolution
played a role in the development of this
trait through natural selection. Amongst
our small, mammalian ancestors, those who
could more quickly recognize a predator at
close range, such as when awoken from
sleep at night, survived to propagate offspring.
This genetic trait was favorably
selected down millions of years of evolution
and contributed to the development of
night myopia.
The underlying optics of night myopia are
an amalgam of various factors, all contributing
to a more near-sighted focus at larger
pupil diameters. For one thing, our dilated
eyes exhibit an effect known as spherical
aberration, wherein the rays at the out edge
of our expanded pupil are focused (prima-rily by the cornea) further in front of the
retina. In addition, there is also the “Purkinje
effect,” wherein the eye’s peak sensitivity
shifts into the shorter wavelength, blue end
of the spectrum at low levels of illumination.
This also makes the eye’s focus more near
sighted. Compounding these two near-sighted
factors is the eye’s tendency to adopt a
focus of approximately three feet when “at
rest,” i.e., either with the eyes closed or with
no distinct object to focus upon (also know
as “empty-field myopia”). These three factors
are generally thought to all contribute to
the phenomenon of night myopia, by reducing
acuity and contrast sensitivity at night.
WHAT WE’VE LEARNED FROM
REFRACTIVE SURGERY
Refractive surgery: Did it spell the end of eyewear
and contact lenses? This was forecasted,
but the current reality is much different.
No doubt, our understanding of vision processing
is much more advanced today, primarily
as a result of the analysis of dissatisfied
refractive surgery clients. Once a term that
generated much concern in the eyewear
industry, refractive surgery (which also
encompasses the more popular “laser surgery”)
has now taken its place as an alternate
refractive-correction choice. Refractive
surgery’s use of abberometry, which produces
a more comprehensive model of the
eye’s focus, has enlightened our understanding
of many of the night-myopia effects
described above. Aberration analysis can
often yield a more accurate and precise
determination of astigmatism and axis than
traditional objective/subjective refraction
techniques. Through a more precise and
complete measurement of the eye’s total
focus, abberometry corroborates that there
are clinically significant focus differences
between smaller and larger pupil openings.
Therefore, there is now a clearly defined
need to test whether different prescriptions
for daytime versus dusk/evening driving are
advisable.
Either the doctor or dispenser (or both)
should discuss and recommend a separate eyewear
prescribed and designed for anyone who
places a premium on vision and night driving
safety. Besides delivering a crisp distance focus,
optimally focused vision delivers superior contrast
discrimination. This is especially important
at dusk and night, where contrast gradients
are notoriously soft. Eyewear for night
driving will employ even the smallest Rx correction.
The lenses may be clear, or if the client
is particularly light sensitive, utilize one of the
new, specialized polarizing hues optimized for
conditions besides bright sunlight. Whether
clear or tinted, premium, hydrophobic antireflection
coatings are mandatory for reduced
ghosting and contrast enhancement.
FIELD-OF-VIEW
As a driver, not only is it important how sharply you
see, but also how much you can see counts with
equal significance. A critical issue surrounding any
optimized eyewear/sunwear for driving is field-ofview.
Most states’ DMV vision regulations contain
minimum standards for a driver’s angular field of
view (FOV) and will restrict deficient candidates
even when their central acuity is 20/20. In New
York, for example, drivers must possess not less than
140 degrees field-of-view (monocular or binocular).
Although recent fashion trends favor larger eye-sizes,
it was not long ago that 45mm to 49mm eye-sizes
were the popular norm for both eyewear and sunwear.
As our clients have already discovered, smaller
sized sunglasses deliver inadequate sun protection.
But smaller eye-sizes also do not allow a truly safe
field of view for driving. The traditional solution for
sunwear has been to choose larger eye-sizes, say
56mm or greater, with a shape difference of 6mm to
9mm. This results in heavier, thicker and more cumbersome
sunwear, and still doesn’t provide an optimal
solution for non-sun driving eyewear
ENTER “WRAP-AROUND” EYEWEAR
Finding first acceptance in plano sunwear for sports,
we are rapidly entering a paradigm shift in lens-form
dispensing. Wrap-around eyewear significantly
increases the driver’s unobstructed FOV, without a
need for large “B” lens dimensions and without
additional weight and thickness. Wrap-around
designs work for both sunwear and regular eyewear.
Up until recently, examination, lens and frame technology
has been based on flatter-form lens curves.
(This is because lens production techniques were
derived from those first optimized for glass.) Note
how most of the latest technology for our popular
aspheric lenses is designed to make them flatter and
thinner. But these flat lenses are unsuitable for use
with newer frames that feature steeper wrap-angles
(also known as “face-form” angle).
Using frame wrap angles of 10 to 25 degrees, along
with lens base curves of six to eight diopters, it is
finally possible to deliver eyewear that can be truly
described as offering a “panoramic” field-of- view…
literally, akin to having a prescription ground in your
windshield. However, there are new vision considerations
that accompany these curved lenses and this
is where a paradigm shift occurs. With non-traditional
values for vertex distance (nine to 11mm) and
pantoscopic lens tilt, an “Rx compensator” program
must be used to ensure sharp central acuity and
binocular fusion with these wrap angles and curves.
There may also be residual issues with peripheral
sharpness and that’s where a whole new generation
of lenses specifically-designed for wrap-around eyewear
come in. Products such as SOLA/Zeiss Spazio,
Shamir Attitude and KBCo’s Wrap Solutions offer
not only an optimized periphery for wrap eyewear
through the use of aspheric and atoric curves, they
also possess a lens form factor that reduces excessive
thickness and weight (for minus powers).
Vision care professionals should also be aware that
wrap eyewear requires pupillary compensation for
the de-centering effects of lens tilt, depending on
degree of wrap angle. Success in wrap eyewear also
depends on using a starting Rx that is fully corrected
for maximum distance focus. In my practice, I have
found that clients enthusiastically receive vision-optimized,
wrap-around single-vision and progressive
eyewear. Although there is an initial perceptual
adjustment, clients love the improved field-of-view
and comfortable fit of wrap eyewear. Starting with
wrap around sunwear, customers eagerly desire the
same “panoramic” vision for special night-driving
eyewear made in the same wrap around form.
EYEWEAR OPTIMIZED FOR DRIVING—
THE HIDDEN SALES POTENTIAL
As sunwear is often cited as the ideal second pair sale,
the time is ripe for vision professionals to unlock the
hidden sales potential of optimized eyewear for driving.
When your client comes says “I’m uncomfortable
with driving in general, but particularly at dusk
and night,” your response should be “With today’s
vision technology, we have a better understanding of
the unique vision processes that affect your eyes when
driving. We’ll be able to show you how an optimized
pair of driving eyewear can restore your feeling of
confidence and safety, particularly at night.” There
has never been a better time, nor a more receptive
audience, for that “third” pair of eyewear. Make your
clients happy and safe, and unlock the profits hidden
in every sale of optimized eyewear for driving.LT
Barry Santini is a New York State licensed optician
based in Seaford, N.Y.
May 2007
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