Note: Descriptions are shown in the official language in which they were submitted.
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PROCEDURE FOR DESIGNING A PROGRESSIVE OPHTHALMIC LENS AND
CORRESPONDING LENS
DESCRIPTION
Field of the invention
The invention relates to a procedure for designing a progressive ophthalmic
lens,
where the lens comprises a far vision area, a near vision area and a passage
that
extends between both areas, where between the far vision area and the top edge
of
the lens there extends a top area and between the near vision area and the
bottom
edge of the lens there extends a bottom area. The procedure comprises the
following stages:
- taking a user's physiological and prescription data,
- selecting a frame,
- taking the frame data, including the data of the frame perimeter, and
- optionally taking the data of the lens position with respect to the user's
eye, taking
into account the selected frame.
The invention also relates to a finished progressive ophthalmic lens as shown
and
the corresponding bevelled progressive ophthalmic lens.
State of the art
Progressive ophthalmic lenses are known comprising the said far vision, near
vision
and passage areas. The far vision area and the near vision area have different
powers and this causes the lens to contain optical aberrations that are
typically
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distributed in the lateral areas on both sides of the power progression
passage,
which are inevitable and inherent to the fact that various differentiated
optical
powers exist. These optical aberrations, which are not desirable but
inevitable, can,
in a non-limiting way, be field curvature, oblique astigmatism, coma, etc..
Various
techniques exist for reducing and distributing these aberrations along the
surface of
the lens so that they affect the user as little as possible. In addition, it
is possible that
the user requires astigmatism correction. This astigmatic correction can also
be
included in the lens by means of so-called prescription astigmatism. Logically
in the
physical lens prescription astigmatism and said optical aberrations coexist in
an
overlapped state, but during the procedure for designing the lens these
characteristics are treated in a differentiated way.
Thanks to existing optical aberration optimization techniques, preferably
referring to
the distribution of the lens power progression associated aberrations, such as
oblique astigmatism, coma and field curvature among others, greater comfort
has
been achieved for progressive lens users and, consequently, said lenses have
become popular. In this specification and claims, the term "lateral
aberrations" will
apply to all those optical aberrations that are the result of progressive lens
power
progression, including, among others, oblique astigmatism, coma and field
curvature.
It is known to take into account various physiological data, such as the frame
chosen by the user, in the procedure of selecting the most suitable
progressive lens
for the user. For example, in certain cases, data are taken on the positioning
of the
lens with respect to the user's eye, taking into account the selected frame.
Examples of this can be found in documents ES 2.253.391 and WO 2009/133887
Al.
Document EP 1.830.222 Al, EP 1.950.601 Al, JP 2004163787 A, and WO
2009/135058 A2 describe different procedures for manufacturing progressive
lenses
that take into account the frame chosen by the user.
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However there is still the need to devise procedures that improve the
treatment of
optical aberrations present on lenses, and very particularly distributing
power
progression associated lateral aberrations.
In this specification and claims, the terminology of the ISO 13666 standard
has been
used, which establishes the following definitions:
- semifinished lens blank: piece of preshaped material that only has one
finished
optical surface,
- finished lens: lens where the two sides have finished optical surfaces,
this finished
lens can be bevelled (to adjust its perimeter to a particular frame) or not.
In this specification and claims, it is considered that the expression
"finished lens"
always relates to the unbevelled lens. For the bevelled lens the term
"bevelled
finished lens" is specifically used.
Disclosure of the invention
The aim of the invention is to overcome these drawbacks. This purpose is
achieved
by means of a procedure of the type indicated at the beginning, characterized
in that
it comprises a lens optimization stage that comprises the following sub-
stages:
- calculating objective power and prescription astigmatism values for the
far vision
area, the near vision area and the passage, according to the user's
physiological
and prescription details and, optionally, the positioning data,
- generating or selecting a predesigned lens, where the predesigned lens
has
certain lateral aberration values, preferably lens power progression
associated
astigmatism, in the top and bottom areas,
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- defining a useful area, defined according to the perimeter of the frame (and
preferably consisting of the area within the perimeter of the frame), and an
outer
area outside the useful area, and positioning the useful area in the lens
(preferably
taking into account the correct position of the lens with respect to the
user's eye
according to the user's morphology), where the useful area divides the top
area into
a top outer area and a top inner area, and the bottom area into a bottom outer
area
and a bottom inner area,
- redistributing at least one of the lateral aberrations on the lens,
preferably a lens
o power progression associated astigmatism aberration, where during the
redistribution the aberration on the chosen lens is distributed around the
outer area
allowing, at least in one of the top outer and bottom outer areas, values to
be
adopted that are higher than those on the predesigned lens.
In this specification and claims, a predesigned lens is to be understood to be
a lens
that is taken as the starting point for the optimization stage according to
the
invention. It is a lens that has been calculated by any method other than that
indicated in this invention, preferably without taking into account the frame
chosen
by the user, and very preferably without taking into account the perimeter of
the
frame. The predesigned lens can have been calculated beforehand, so that the
optician can have a plurality of predesigned lenses from which he can chose
the
most suitable one when performing the optimization according to the invention,
or it
can be a lens that is generated (calculated) when performing the optimizing
according to the invention.
Effectively, usually conventional progressive lenses (and the predesigned
lenses
that are usually used in designing conventional progressive lenses) have been
calculated without taking into account the frame that will be used by the
user.
Consequently, the exact location of the useful area is not known. As a result,
conventional lenses (and conventional predesigned lenses) try to maintain the
top
and bottom areas with lateral aberration values, particularly for progression
associated astigmatism, as low as possible since the whole of that part of
said top
and bottom areas that in the end remains inside the useful area will be an
area used
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frequently by the user, and it is unknown beforehand what size this will be,
and so it
is necessary to extend said areas to the total diameter of the lens in order
to cover
any possible frame shape. Therefore, the existence of lateral aberrations with
noticeable values in these areas would be a source of discomfort for the user
if in
the end they remain within the perimeter of the user's frame. However, in this
invention it is taken into account that, whereas in the top inner and bottom
inner
areas the presence of lateral aberrations is highly inadvisable (and must be
reduced
to a minimum), on the other hand in the top outer and bottom outer areas any
value
of lateral aberrations is possible (and, in fact, any aberration) since in the
end these
areas will be eliminated during the bevelling, and so their optical properties
are
totally irrelevant. On the other hand, when redistributing the lateral
aberrations
(preferably the distribution of progression associated astigmatism) by
allowing the
top outer and bottom outer areas to adopt values higher than those on the
predesigned lens it is possible to achieve that in other parts of the lens,
specifically
within the useful area, the values of the lateral aberrations are reduced
and/or
softened, which improves user comfort.
It is not necessary that the optimization process simultaneously affects both
areas
(the top outer and bottom outer areas), as there may be an optimization that
only
affects one of therm
Generally, the optimization can include treating one of the lateral
aberrations
(preferably the lens power progression associated astigmatism) or more than
one.
Therefore, when referencing the chosen lateral aberration in this
specification and
claims, it must be understood to also include cases where more than one
lateral
aberration has been chosen.
Preferably the chosen lateral aberration is redistributed via a redistribution
process
wherein a non null objective value of the chosen lateral aberration is defined
for at
least one of the top outer and bottom outer areas, with the objective value
preferably
being between 30% and 70% of the maximum value present in the useful area for
said lateral aberration, and very preferably between 40% and 60% of the
maximum
value present in the useful area for said lateral aberration. Effectively, as
already
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mentioned, the usual procedures try to make the lateral aberrations as small
as
possible in the top and bottom areas, and so the objective values are usually
0.
Also, in conventional procedures the top and bottom areas are not divided
according
to the frame (which, when defining the useful area, divides them into top
outer, top
inner, bottom outer and bottom inner), and so there is not a differentiated
treatment
of these sub areas. When a predesigned lens is selected, these 4 areas have
lateral
aberration values that are null or very small. When non null objective values
(or
even clearly high values) are fixed to the outer areas (top outer and/or
bottom outer)
a redistribution of the lateral aberrations is forced around the whole lens,
obtaining a
to reduction and softening of the lateral aberrations in the useful area,
particularly in
the temporal and nasal area.
Advantageously, in the optimization process initial parameters are established
that
comprise objective power values, objective chosen lateral aberration values,
power
and chosen lateral aberration tolerance values and a weight function, where
the
optimization process is carried out using a merit function, where, for the
outer area,
chosen lateral aberration tolerances are established that are greater than the
chosen lateral aberration tolerances envisaged in the useful area.
Effectively,
allowing greater tolerances in the outer area allows the chosen lateral
aberration to
be redistributed along the outer area "freely". Conceptually, the ideal
situation would
be that the tolerances in the outer area were infinite, but to avoid numerical
calculation problems, the infinite value is replaced with a value that is high
enough
to achieve the desired effect.
Preferably weight function values are established for the outer area that are
smaller
than for the useful area, preferably standardised values are established that
are less
than 0.2, very preferably less than 0.1. Effectively, this way the weight
function does
not take into account (or does so only slightly) what occurs in the outer
area. Ideally,
the weight function has a value 0 in the outer area, but again for calculation
purposes, it is preferably that the value is not exactly 0, and so it is
replaced with a
value that is small enough to achieve the desired effect (that what happens in
the
outer area is not important for the merit function). Preferably the weight
function is
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standardised (takes values between 0 and 1), in which case the weight function
values in the outer area are smaller than 0.2, or even smaller than 0.1.
Advantageously, in the optimization process a shifting stage is performed of
at least
one of the nasal and temporal maximums of lens power progression associated
astigmatism, that is present in the predesigned lens, moving it away from the
far
vision and near vision areas and passage. Effectively, both maximums (nasal
and
temporal) are present in conventional progressive ophthalmic lenses. As
already
mentioned above, predesigned lenses are calculated without taking into account
any
frame, and so it frequently occurs that these maximums remain within the
useful
area. This invention proposes moving them away from the far vision and near
vision
areas and passage, in other words, separate them to the right and left,
bringing
them closer to the respective nasal and temporal edges. Preferably these
maximums are shifted by means of localised changes in the spline surfaces that
describe the objective progression astigmatism and which comprise said
maximums. Ideally the maximums are shifted until they reach the edge of the
useful
area. However, again for calculation purposes, it is advantageous that the
maximum
is not exactly on the edge of the useful area (to avoid calculation
singularities), and
instead it is advantageous that the maximum coincides substantially with the
perimeter of the useful area. Substantially means that it is sufficiently
close so that
being any closer does not mean improving the distribution of the progression
associated astigmatism that is noticeable to the user.
It is not essential that both maximums are shifted simultaneously, but rather
that the
procedure can include shifting only one of the maximums.
Alternatively, the perimeter of the useful area (which is the perimeter of the
frame
chosen by the user) can be replaced with nasal and temporal benchmarks of the
useful area perimeter, and at least one of the maximums is shifted until it
coincides
substantially with its respective nasal or temporal benchmark, respectively.
Effectively, using these benchmarks simplifies the calculation and makes it
possible
to obtain satisfactory results.
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Shifting the maximums locally affects the distribution of powers and
progression
derived astigmatisms. Preferably these changes are obliged not to affect the
distributions of power and progression associated astigmatism in the far
vision and
near vision areas and passage.
Preferably an ellipse of vision is defined. The ellipse of vision is the
section of the
useful area that has greater ocular transit and, therefore, it is the section
that is used
most by the user. Logically, it comprises the far and near vision areas and
passage.
Preferably it is centred in the prism control point. Preferably its semi axes
are
calculated from the users gazing angles and vertex distance. Preferably it is
considered that the vertex distance is between 24 and 32 mm (very preferably
between 27 and 29 mm). Preferably it is considered that the vertical gazing
angle is
between 350 and 45 (very preferably between 38 and 42 ), and that the
horizontal
gazing angle is between 25 and 350 (very preferably between 28 and 32 ). A
particularly advantageous solution is obtained when the larger semi axis is 23
mm
(corresponding to a gazing angle of 400 with respect to the centre of the
user's eye
and considering a vertex distance of 28 mm) and the smaller semi axis is 16 mm
(corresponding to a gazing angle of 30 with respect to the centre of the
user's eye
and with the same vertex distance of 28 mm). This ellipse of vision is used to
give
the corresponding area a "favourable treatment", in the sense that worse
optical
characteristics are required of it than of the far and near vision areas and
passage,
but better ones than the rest of the useful area. Preferably this is done by
assigning
higher weight function values to it than to the rest of the useful area.
The invention also relates to a finished progressive ophthalmic lens, where
the lens
comprises a far vision area, a near vision area and a passage that extends
between
the far vision area and the near vision area, where between the far vision
area at the
top edge of the lens there extends a top area and between the near vision area
and
the bottom edge of the lens there extends a bottom area, characterized in that
it
comprises a useful area, defined according to the perimeter of a certain
preselected
frame, and preferably consisting of the area comprised within the perimeter of
the
frame, and an outer area outside the useful area, where the useful area
divides the
top area into a top outer area and a top inner area and the bottom area into a
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bottom outer area and a bottom inner area, where in at least one of the top
outer
and bottom outer areas there is a lens power progression associated
astigmatism
greater than 0.25 Dp.
Preferably the top inner and bottom inner areas have a lens power progression
associated astigmatism less than 0.12, preferably less than 0.06.
Brief description of the drawings
Other advantages and characteristics of the invention will be appreciated from
the
following description, wherein, in a non-limiting manner, preferable
embodiments of
the invention are described, with reference to the accompanying drawings,
wherein:
Figs. la and 1 b, diagrams of progressive ophthalmic lenses with the various
areas
identified in this specification and claims.
Fig. 2, a diagram of a progressive ophthalmic lens with the perimeter of the
frame
and the ellipse of vision.
Figs. 3a, 3b y 3c, diagrammatic views of some distribution maps of progression
associated astigmatism, such as examples of lateral aberrations, showing the
movement of the progression associated astigmatism according to the procedure
of
the invention.
Figs. 4a and 4b, distribution maps of the weight functions according to the
invention.
Figs. 5a and 5b, the distribution map of the progression associated
astigmatism of a
progressive ophthalmic lens before and after applying the optimizing procedure
according to the invention.
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Detailed description of some embodiments
In this specification and claims various parts of a finished progressive
ophthalmic
lens have been mentioned. Figs. la and lb diagrammatically show each one of
Fig. 2 shows another example of ophthalmic lens with useful area 13 defined by
the
frame, in which the ellipse of vision 33 has been included. Generally the
shape of
useful area 13 coincides with the surface defined by perimeter 11 of the
frame, but it
20 does not have to be that way. Useful area 13 can have other geometries
which,
although they are defined by perimeter 11 of the frame, do not coincide
exactly . So,
for example, it is possible to define useful area 13 as that defined by the
rectangle
formed by top 25, bottom 27, nasal 29 and temporal 31 benchmarks. Or it is
possible to define the useful area as some other simple geometric shape that
that will remain outside the frame (in other words, outer area 15) once the
lens has
been bevelled. This way lenses with less lateral aberrations (and, in
particular, with
less progression associated astigmatism) can be obtained, because they are
made
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more comfortable for users regardless of the type of progressive design
chosen,
which will not vary in the areas that are important for vision (far vision
area 1, near
vision area 3 and passage 5). The examples in Figs. 3a, 3b, 3c, 5a and 5b show
cases where the chosen lateral aberration is progression associated
astigmatism.
However, the results and conclusions can be generalised to any other lateral
aberration. Fig. 3a shows the progression associated astigmatism of a standard
design. Perimeter 11 of the frame chosen by the user, represented
diagrammatically
by a rectangle, has been marked on the finished lens. It can be seen that
there are
large areas with zero astigmatism or nearly zero, which in the end will be
eliminated
during the bevelling operation. Given that when designing the progressive lens
the
frame finally chosen by the user is not known and given that the areas above
far
vision area 1 and under near vision area 3 can be very important optically
(since, if
they remain within perimeter 11 of the frame they will be areas used
frequently by
the user), conventional progressive lens design techniques tend to keep top
area 7
and bottom area 9 with the least astigmatism possible and, generally, with the
smallest aberrations possible. However, in reality, an important part of these
top 7
and bottom 9 areas will be eliminated during the bevelling, in particular top
outer 19
and bottom outer 23 areas. Consequently, conventional progressive lens design
techniques are conditioned by trying to optimise the optical properties of
areas that
will be eliminated subsequently. The procedure of this invention provides an
improvement by distinguishing between useful area 13 and outer area 15. This
way,
in this example, during the procedure according to the invention progression
associated astigmatisms are redistributed as shown in Figure 3b. In other
words, top
outer area 19 and bottom outer area 23 are "invaded" with astigmatism which
leads
to a reduction in the maximum astigmatism values presents in useful area 13.
Given
that in the end only useful area 13 will remain, the overall result is a
bevelled lens
with smaller astigmatic aberrations caused by progression. This is shown in
Figure
3c.
The methodology used is as follows:
- First of all, based on the physiological data of the user and the frame
chosen by
the user, a set of distances and values are determined which preferably now
include
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the correct positioning of the lens with respect to the eye taking into
account the
morphology of the user and the frame.
- Then the top 25, bottom 27, nasal 29 and temporal 31 benchmarks of useful
area
13 are determined, together with the now conventional data, such as for
example
the positions of near vision 3 and far vision 1 areas, and passage 5. Also the
value
and position of ellipse of vision 33 are determined, centred in the prism
control point
35.
- Objective power and prescription astigmatism values are determined for far
vision
area 1, near vision area 3 and passage 5 according to the previous data.
- A predesigned lens is generated or selected that is a good starting point
for the
optimization process.
- With all the above information the initial values are determined for the
optimization
process. In particular, progression associated astigmatism and objective power
values are determined as well as progression associated astigmatism and
objective
power tolerance values. Preferably the permitted progression associated
astigmatism (as objective value) in top outer 19 and bottom outer 23 areas is
between 40 % and 60 % of the maximum progression associated astigmatism
present in useful area 13. As for the progression associated astigmatism
tolerances,
preferably a tolerance of between 80 % and 120 % above the maximum permitted
tolerance in useful area 13 is admissible. In addition, the areas that have 0
dioptres
(Dp) as the objective value of progression associated astigmatism are
preferably
assigned a tolerance of 0.06 Dp. Also the weight function is determined,
preferably
taking into account ellipse of vision 33. Preferably the shifting stage of the
nasal and
temporal maximums of progression associated astigmatism is performed. This is
done preferably by introducing changes in the control points of the spline
surfaces
that define the surrounds of the maximums, so that localised changes are
generated
that shift these maximums, but which do not affect the optical properties of
the lens
in its central sections, particularly in near vision 3 and far vision 1 areas
and
passage 5.
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- Then the progression associated astigmatism is redistributed, as mentioned
above.
Once the surface to be machined has been determined by means of the optimizing
process, said surface is machined (usually it is the concave surface of the
lens) to
thus obtain the finished progressive ophthalmic lens. Finally the lens can be
bevelled to thus obtain the end product suitable for being mounted in the
frame.
Fig. 4a shows a distribution map of weights according to the invention.
According to
a preferred solution of the invention, the weight function has been
standardised, so
that its values range from 0 to 1. It is possible to approximately recognise
the
various areas of the lens, such as the far vision 3 and near vision 1 areas,
and
passage 5, perimeter 11 of the frame and ellipse of vision 33. In this
particular
example, the part of outer area 15 that remains within ellipse of vision 33
has a
greater weight than the other parts of outer area 15. Although, as already
mentioned, this part of ellipse of vision 33 will be eliminated in the end,
nevertheless, by giving it a greater weight than the rest of outer area 15, it
is
possible in certain cases to obtain better results in useful area 13 (and/or
greater
processing speed). Also it is observed that the intersection of useful area 13
with
ellipse of vision 33 has a greater weight than the other parts of useful area
13.
Finally it can be observed how near vision 3 and far vision 1 areas and
passage 5
are assigned the greater weight. In Fig. 4b another weights distribution map
can be
observed in which perimeter 11 defines the area of the lens on its own with a
weight
less than 0.2.
Figs. 5a and 5b show a comparative example between a distribution map of
astigmatisms in a conventional lens, over which perimeter 11 of the frame
chosen
by the user (Fig. 5a) has been superimposed and a distribution map of
astigmatisms
in a lens according to the invention (Fig. 5b). In this particular case during
the
optimization, the astigmatism has only been redistributed around bottom outer
area
23. Comparing both maps it can be observed that useful area 13 designed
according to the invention has smaller progression associated astigmatism
values
and a softer distribution of said values.
