Impression FreeSign® - Innovative Perfection
FREE-FORM TECHNOLOGY
Modern lens design technology is progressively improving each year
and improvements are being made with just about every new design
manufactured. This has led to the free-form optical lens design
technology that can actually optimize, or optically refine, the
progressive lens design for a given prescription by applying
appropriate asphericity at various points across the lens surface.
Practitioners need to submit the prescription, frame with the pupil
centration points, vertex distance and pantoscopic and/or face-form
tilts to the laboratory. With all these parameters considered, the
design process then determines the optimum form of the concave
surface so the resultant lens is custom designed for the individual
fitting of the frame. See Figure 1. Having been recorded, these
parameters are input into the computer and the lenses are then
custom made for the wearer's prescription.
The PAL's are
also designed according to the vertical frame measurements; that
will also determine the length of the corridor. The vertical
direction of gaze from the point where the distance prescription is
measured, which lies between 2 and 4 mm above the distance fitting
cross and the near vision circle, can range between approximately 30
and 500 depending on the vertical measurement of the frame.
Free-form technology compensates for this by applying sufficient
amounts of asphericity at these points in order to neutralize the
aberrations that would normally be produced at such viewing angles.
The computer takes into account the pantoscopic tilt angle
and frame depth and will make the necessary adjustments to the
design of the lens and the necessary compensation for the lens power
so that the tilted lens has the same effect as the untilted one.
What this means is that the prescription ordered will differ
slightly from the one received.
The advantage of
free-form optical optimization design lenses is that the geometrical
inset is no longer dependant on the convex surface geometry when the
inset is fixed by the progressive surface geometry, but can be
calculated individually for the lens prescription. These designs are
individually computed for each lens from the knowledge of the
prescription data and base curve of the lens. Concave atoric
surfaces allow wider corridors and less unwanted peripheral
astigmatism. Atoric concave surfaces combined with low-base
aspherical progressive power surfaces are computer generated to
produce optimal performance in each zone of the lens. If astigmatic
compensations are required, the astigmatic compensations are also
incorporated on the concave surface
The customer needs a broad visual field for the distance and a
"stable" image with a very light distortions, because he uses vision
at the distance during the majority of her occupation. His habitual
equipment is composed of progressive glasses with a length of 18 mm
progression.
Optimum resolution:
The point VL (DF) is positioned underneath the centring
cross (-2 mm). This allows to give a broad field of vision for the
distance. To find a good combination between a broad visual field
from a distance and a length of classical progress, the point VP (DN)
must be located in - 19 mm. The length of progress of the new glass
is therefore 17 mm.
The customer needs a very broad zone of intermediate vision with
little distortions, because he works the majority of the time in
intermediate zone (medium distance). His habitual equipment is
composed of progressive glasses with a length of 18 mm progression,
The customer do not want to read the most of the time.
Optimum resolution:
The point VL (DF) is slightly displaced (3 mm)
above. The point VP (DN) is ideally located in - 19 mm to allow the
"down gaze" to be similar to the previous situation. This design
allows to acquire a broad intermediate visual field, and less
distortions in the intermediate distance. In that case the Length of
progression is therefore 22 mm.
The customer needs a very broad field of vision at near, He must
less look down than with his habitual progressive spectacles,
because he works mostly at near, His habitual equipment is composed
of progressive glasses with a length of 18 mm progression
Optimum resolution:
The point VL {DF) is positioned above the centring
cross {2 mm). The point VP {DN} is ideally located in 15 mm This
glass allows the porter to have a broad visual field at near with a
small
"down gaze", The length of progression is therefore 17 mm.
Impression FreeSign® - Innovative Perfection
There has never been anything like it - the new Impression FreeSign®
progressive lens is matched to your personal vision needs and
simultaneously to your individual parameters for the first time.
The benefits at a glance:
Even the look isn't missed out. Due to the perfect coordination with
your frame, the lenses are optimally thin and aesthetic.
