Our eyes are like our
fingerprints or snowflakes. Each one is different. Even our right
and left eyes are not exactly the same. Because of this, how light
enters our eye is also very specific and individualized. With this
knowledge, it’s only logical that eyeglass lenses follow a more
personalized path.
Wavefront technology starts
with the abberometer. This is an instrument that precisely records
the imperfections of the eye. An eye care professional will shine a
low intensity laser into a patient’s eye, instructing them to
focus on the light. As the light is reflected off the retina,
through the lens and through the cornea, it will be distorted by the
imperfections of the eye’s visual system. The abberometer has a
host of various lenses that the light will pass through. This will
be recorded as spots by a special camera. The amount that the spots
deviate from their original location determines how much and where
the visual issues are. The result is a map of sorts that aids a
surgeon, or a lens designer, to know what changes to make to create
optimum vision.
Wavefront is superior to a
conventional refraction in that it addresses higher order focusing
issues beyond hyperopia, myopia and astigmatism. In laser surgery,
this technology guides the laser to remove the exact amount of
corneal tissue needed to produce superior vision. How does this
apply to eye glass lenses?
Izon by Ophthonix is one of
the newer truly custom lenses. Using a proprietary aberrometer to
take an ‘iprint’ of the eye, the lenses are created using
wavefront technology. The mapping allows the amount of power ground
in the lens to be digitally ground into the back side of the lens.
The peripheral edges of the lens are crafted to provide superior
vision in all areas.
There is more to this than
abberometers and wavefront mapping. To create these new generation
lenses, there is required software for lens design, machine control
and lab integration. Also, specific tools for lens fabrication are
to be considered. To make a true custom lens, a myriad of cutting
combinations must be available. Digital surfacing also creates
versatility by allowing front and back surfacing as well as a
combination of the two.
Some lenses that have been
labeled as custom or freeform lenses don’t truly fit that
definition. Is the lens directly digitally surfaced, or rather a
digitally surfaced mold?
True free form optics or
customized lenses are made from a digitally made mold, using a
program that simulates the patterns of human vision and incorporates
that information into the design. This design is digitally cut into
the mold, bypassing the more conventional ceramic model and glass
mold.
A personalized free form lens
begins with a lens with a spherical base curve on the front.
Grinding on the back side of the lens, or other fabrication methods
such as splitting the add power between the front and back, produces
better optics and wider fields of vision, a benefit to all
progressive lens wearers.
Another type of high
definition lens is one that does not use such individualized mapping
for each lens. Instead it considers factors such as the patient’s
prescription, frame selection, lens material index of refraction,
center thickness, distance from the eye to the back vertex of the
lens, distance from the eye to the object, pupil distance, and
pantoscopic tilt, among others. These factors are matched with
selected base curves and grinding methods to produce a lens that
results in a pronounced increase in visual clarity.
Examples of these lenses are
the Varilux® Ellipse® 360°, Varilux® Physio® 360° by Essilor,
the Creation® and Autograph® by Shamir, the Kodak Unique® by
Signet Armorlite, GT2 by Zeiss , SolaONE HD, Sola Compact Ultra HD,
and the Seiko Succeed, among others.
“High Definition” brings
to mind computer and television screens with extremely vivid and
sharp images. How does this transfer to eye glass lenses?
Both wavefront mapping and
digital casting methods create a host of new generation PALs. The
ability to additionally personalize the lens creates more clarity,
vividness, and depth than more conventional lenses.
When educating patients
on
their lens options, it is important to mention the newest
advancements in lens technology. Explain how these lenses will
provide crisper vision with vivid colors and added contrast.
Patients do not need to worry about settling for an aesthetically
inferior lens to get superior vision. High Definition lenses are
available in a host of lens materials such as CR-39 (standard
plastic), various high index plastics, Trivex, and polycarbonate.
Options such as Transitions®, polished edges, and anti-reflective
coating help to create an optimum visual experience for the patient.
When matched with an
anti-reflective coating, these lenses can provide optimal vision in
many environments and conditions.
Although all eyeglass wearers
appreciate being able to see finer detail and a fuller spectrum of
color, patients with vision loss due to an illness such as macular
degeneration will notice the superior vision. The lenses will be
beneficial for many patients both alone and in concert with low
vision aides.
Many of the terms used to
describe these new progressives can be very confusing, and may not
be the best description. As technology in the optical industry
advances, there will be more buzz words added to the mix. The goal
should be to educate yourself about the individual lenses and what
would be the best for the patient.
