Free FormPresentation Notes
FreeForm Lens Technology
What does it really mean to your Patients and your Business?
Definition:
Free-form surfacing refers to a process that is capable of producing complex surface shapes, including
aspheric, atoric and even progressive addition surfaces. A typical process begins by generating the lens
surface using a three-axis, computer numerically controlled (or CNC) generator. With three possible axes
of movement, single-point cutting tools can produce virtually any lens surface shape with a high degree of
accuracy and smoothness. The worked lens surface is then polished to a high luster using a flexible
polishing pad that is also dynamically controlled by a computer.
Using free-form surfacing, the laboratory can directly surface a variety of lens designs directly onto a
semi-finished lens blank in addition to the prescription curves. With two surfaces to work with, free-form
progressive lenses represent a combination of factory-molded and free-form-surfaced lens curves that
range in complexity from simple spherical surfaces to progressive surfaces that have been combined with
the prescription curves.
Slide 9
The software can calculate the “perfect” curve(s) and cylinder cross-curve(s) to 1/100th of a diopter
(0.01D), the optimal corridor length based upon the fitting height and frame “B” measurements, and the
near vision inset based upon add power and PD. The free-form machinery
available today can produce those curves.
Slide 14
CNC – Computer Numeric Controlled – processing enables industries to consistently produce parts to accuracies
undreamed of a few years ago.
The same part can be reproduced to the same degree of accuracy any number of times with amazing speed. Prerequisitions:
- Computer properly programmed
- Machine properly set up
Glossary of the Terms you need to Know
LENS PERSONALIZATION
You’ve probably already heard the analogy that lens personalization is like buying clothing: you can buy
S, M, or L, or you can buy a defined size, or you can have the item custom tailored to fit you perfectly.
That’s exactly what lens personalization is—custom tailored to meet the wearer’s exact prescription
requirements, working distance needs, frame measurements, and posture.
HUNDREDTHS
One way of personalizing lenses is to provide them to 0.01D accuracy instead of 0.25D accuracy. Prior to
lens personalization, most lenses were produced in +/-0.25D increments.
OPTIMIZATION
One of the techniques free-form PAL designers use is called optimization. This strategy attempts to
provide lenses that are as sharply corrective as possible. This means that designers will address lens
aberrations in order to provide the wearer with lenses that offer super crisp vision.
ABBERATIONS
SPHERICAL ABERRATION When a wide beam of parallel light rays pass through a lens that has plus
or minus power, the light that passes through the center of the lens will come to a fine focus, however, the
rays of light passing through the lens’ periphery will focus either in front of or behind the ideal focal point.
In vision-correcting lenses, this results in an imperfect correction of vision. Spherical aberration is most
noticeable when the pupil is dilated (for example, during night driving), or after certain refractive surgeries
like LASIK or a corneal graft.
COMA This optical aberration causes a wide beam of off-axis light to focus inaccurately. Coma is usually
demonstrated by using a wide beam of light and passing it through a lens, which results in an inaccurate
focusing of the rays and the image being blurred. Instead of the light rays focusing to a single point, the
image appears to have a “tail” (like a comet, and hence the coma name). Coma is often troublesome to
wearers viewing street lights or other bright light sources at night. In this situation, they see a starburst
pattern around the light, which is the visual effect of the coma aberration.
MARGINAL ASTIGMATISM This aberration is sometimes called oblique or radial astigmatism. It’s a
result of a narrow beam of parallel light rays passing through a lens at an oblique angle. The light then
comes to a focus at two different points on the retina, and the space between those points determines the
amount of astigmatism the person experiences. Marginal astigmatism is considered to be the most
troublesome lens aberration because it creates unwanted cylinder so all manufacturers work to reduce it.
HIGHER ORDER ABERRATIONS Most lenses address lower order aberrations. That’s because they
attempt to correct spherical and cylindrical refractive errors of the eye. Some lens manufacturers have
introduced lenses that attempt to address higher order lens aberrations. These aberrations affect the quality
of clear vision as well as the contrast of what the lens wearer experiences, which can have a significant
effect on the overall visual experience with correcting lenses. Up to 20% of a person’s visual potential can
be reduced due to higher order aberrations.
POSITION-OF-WEAR
One technique that lens manufacturers use to personalize lenses is the use of position-of-wear (POW)
measurements. In addition to the typical patient PDs and fitting heights, ECPs are asked to also supply
vertex distance, pantoscopic tilt, and face-form (wrap) tilt measurements. This is because these
parameters have an effect on the power wearers experience when they wear their lenses.
VERTEX DISTANCE
The position at which a lens is placed in front of the eye has a bearing on the power it will deliver to the
wearer. This optical property is known as “positional effect.” For example, a patient may have been
refracted with the refractor setting 10mm in front of her eyes but when she obtained her eyeglasses, the
lenses sat only 7mm from her eyes. If the patient was refracted with a +10.00D power, the wearer would
experience +9.50D in the lenses delivered to them. That 0.50D apparent loss in effective power is due to a
change in the lens’ position between the refracted position and the delivered position.
LENS TILT
When patients are refracted using a conventional phoropter, the instrument is usually placed at roughly a
90° angle in front of their eyes, however that is seldom the POW for the final spectacle product. This
means that most refractionists do not attempt to refract with lenses in a tilted position just as the patient
will wear them. The theoretically correct amount of lens tilt for a patient is 8° and most lens wearers have
their frames positioned at about 8° to 15° of pantoscopic tilt.
FACE-FORM
Sometimes referred to as “wrap,” face-form tilt is another form of lens tilt that occurs when a frame is
curved or “wrapped” around the face’s contour. Wrap sunwear is a good example of this. Sports
performance sunwear is usually highly wrapped to provide eye protection and aggressive good looks but
it also induces unwanted cylinder in the 90th meridian if not compensated.
EYE AND HEAD MOVERS
Is the patient sitting before you an eye mover or a head mover? The answer has a bearing on how the
patient will use their lenses. For example, a head mover will look more along the vertical midline portions
of the lens for most visual tasks because he will turn his head to view objects, reducing the amount of eye
turning. An eye mover will do the opposite: she’ll turn her head a little to view a peripheral object and
turn her eyes a good deal. This means she’ll use the peripheral portions of the lens more.
EYE DOMINANCY
Along with other initiatives to improve the resulting image, one manufacturer has included eye
dominance in the mix of personalized measurements. This is to ensure that both eyes are working as a
single visual system which allows for synchronization of the retinal image, and improved spatial
perception. The design works around the principle that the dominant eye reaches the object first when the
wearer changes their direction of gaze. That also requires that the practitioner use the lens company’s
proprietary measurement system.
MEASUREMENTS
As the design of spectacle lenses has become more sophisticated, the need for accurate measurements has
increased. Unfortunately, the technology for taking lens measurements has remained fairly constant for a
good number of years and the tools used for taking lens fitting measurements still include a PD ruler,
marking pen, and a corneal reflex pupilometer.
In the last few years, instrument manufacturers have begun producing electronic platforms that take
electronic measurements. Since these instruments use electronic imaging and computerized measuring
techniques, they provide highly accurate measurements…as long as the patient is properly positioned and
aligned in the unit.
These instruments, which you might call computerized eyewear selection, measurement, and information
systems (CESMIS), provide highly accurate measurements, usually at the push of a button. To take lensfitting measurements, the selected frame is pre-adjusted, and the patient is positioned and aligned in front
of the instrument. At this point, the optician presses a button and digital images are taken, which the
instrument uses to provide a variety of eyewear and lens fitting measurements. These include:
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Monocular PDs for both distance and near (calculated at actual working distance)
Lens vertex distances
Monocular segment heights
Pantoscopic/retroscopic tilt
Frame wrap (face-form tilt)
Some lens companies will not accept orders for their premium products without POW information, and
sometimes only POW information from their proprietary CESMIS.
Most of these devices also provide accurate frame measurements including the A, B, DBL, and ED.
Another nice feature is that most units allow patients to align to the instrument using their natural body
posture so if a patient has a natural head or chin tilt, it will be considered in the measurements. The
measuring process is fast and accurate and most patients find it interesting, impressive, and engaging.
For the office that does not want to dedicate the space for a stand-alone CESMIS, the answer might be
very simple: There are “apps” available that allow these measurements to be taken with a cell phone,
tablet, or digital camera. The most common ones use Apple’s iPad format. These devices are fast,
convenient, and they don’t take up much space.
Standard Distance Lens
Digital Freeform Distance Lens
Offer clear vision centrally and have distortions and Offer a larger area of clear, natural and distortionimperfections that impact vision to the side
free vision.
Slide 24
leaning forward with reading glasses
tilting head up with bifocals
What you might tell your Patient
natural posture with Freeform
computer lenses
Think about the first time you saw high-definition television. Remember how it made your old analog TV
picture seem drab and blurry? High-definition made colors brighter, shapes sharper, and brought
everything keenly into focus. Now imagine having the same experience with your glasses. Sure, you can
probably see fine with the ones you have, just like watching analog TV was fine when that was all you
had.
But what if you could upgrade to high-definition for your eyes?
Free-form Technology
There’s a new technology that could change the way you see—forever.
It’s called “free-form,” a revolutionary digital manufacturing process that uses computer-aided design and
surfacing to create high-level, customized eyeglass lenses with your unique prescription.
Think of it as a tailor for your eyes. Just like you can take an off-the-rack pair of pants and have it
customized to fit your specific measurements, you can now have lenses made customized for your
specific prescription and frames.
Benefits of Customized Free-form Lenses
Many leaders in the vision industry expect free-form technology to be the next revolution in vision
correction.
In addition to the improved visual clarity that customized free-form lenses provide, you will enjoy:
Exceptional night/low light vision:
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Free-form lenses can reduce glare and halo effects caused by light sources at night, such as car
headlights
Exceptional contrast perception:
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Free-form lenses can sharpen vision
Exceptional color vision:
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Free-form lenses can maximize the optics built into your lenses, providing brighter and more
intense colors
While everyone can benefit to a certain extent from customized lenses, people with complex prescriptions
and progressive wearers will notice the greatest visual improvements.