U.S. patent application number 15/494151 was filed with the patent office on 2018-10-25 for computer implemented method of determining a base curve for a spectacle lens and method of manufacturing a spectacle lens.
The applicant listed for this patent is Carl Zeiss Vision International GmbH. Invention is credited to Ralf-Roland Sauer, Markus Welscher, Helmut Wietschorke, Christoph Winter.
Application Number | 20180307058 15/494151 |
Document ID | / |
Family ID | 62165526 |
Filed Date | 2018-10-25 |
United States Patent
Application |
20180307058 |
Kind Code |
A1 |
Welscher; Markus ; et
al. |
October 25, 2018 |
COMPUTER IMPLEMENTED METHOD OF DETERMINING A BASE CURVE FOR A
SPECTACLE LENS AND METHOD OF MANUFACTURING A SPECTACLE LENS
Abstract
A computer implemented method of determining a base curve value
representing a base curve for a front surface of a spectacle lens
comprises the steps of receiving individual prescription data and
determining the base curve value for the front surface of the
spectacle lens based on the prescription data. The base curve value
is calculated from the received prescription data based on a
functional relationship between one or more values included in the
prescription data and the base curve value.
Inventors: |
Welscher; Markus; (Aalen,
DE) ; Wietschorke; Helmut; (Aalen, DE) ;
Sauer; Ralf-Roland; (Huettlingen, DE) ; Winter;
Christoph; (Huettlingen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carl Zeiss Vision International GmbH |
Aalen |
|
DE |
|
|
Family ID: |
62165526 |
Appl. No.: |
15/494151 |
Filed: |
April 21, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02C 7/027 20130101;
G02C 7/02 20130101; G02C 7/063 20130101; G02C 7/028 20130101; G02C
2202/08 20130101 |
International
Class: |
G02C 7/02 20060101
G02C007/02; G02C 7/06 20060101 G02C007/06 |
Claims
1. A computer implemented method of determining a base curve value
representing a base curve for a front surface of a spectacle lens,
the method comprising the steps of: receiving individual
prescription data; and, determining the base curve value for the
front surface of the spectacle lens from the received individual
prescription data; wherein said determining the base curve value is
done by calculating it from the received individual prescription
data based on a continuous, non-constant functional relationship
between at least one value included in the individual prescription
data and the base curve value, wherein the at least one value
included in the individual prescription data comprises at least one
of: spherical power and object distance, spherical power and
cylindrical power and optionally object distance, spherical power
and cylindrical power and axis and optionally object distance,
spherical power and prismatic power and optionally object distance,
and, spherical power and cylindrical power and prismatic power and
optionally object distance; and, wherein each value included in the
individual prescription data is for at least one of far vision and
near vision.
2. The computer implemented method of claim 1, wherein the values
representing spherical power and representing cylindrical power
which are included in the individual prescription data are divided
into at least two domains of values and the continuous,
non-constant functional relationship between values included in the
individual prescription data and the base curve value depends on
the domain that the value representing spherical power and the
value representing cylindrical power contained in the prescription
data are part of.
3. The computer implemented method of claim 1, wherein said
determining the base curve value is done by calculating it from the
received individual prescription data based on a continuous,
non-constant functional relationship between at least the spherical
power and a preset curvature of the rear surface.
4. The computer implemented method of claim 1, wherein the minimum
curvature of the rear surface is constant for a domain of
prescription data and the base curve results from the dioptric
requests of the individual prescription data and optionally the
data of the as-worn position and optionally the frame data.
5. The computer implemented method of claim 1 further comprising
the steps of: receiving at least one of as-worn position data and
frame data; and, taking into account at least one of the received
as-worn position data and the received frame data when calculating
the base curve value.
6. A method of manufacturing a spectacle lens comprising the steps
of: providing individual prescription data and optionally
individual as-worn position data for the spectacle lens to be
manufactured; determining a base curve value for the front surface
of the spectacle lens element based on the individual prescription
data and optionally based on the individual as-worn position data;
providing a spectacle lens element with a front surface and a rear
surface; and machining the spectacle lens element based on the
individual prescription data and optionally based on the individual
as-worn position data; wherein said determining the base curve
value is done by calculating it from the received individual
prescription data based on a continuous, non-constant functional
relationship between at least one value included in the individual
prescription data and the base curve value, wherein the at least
one value included in the individual prescription data comprises at
least one of spherical power and object distance, spherical power
and cylindrical power and optionally object distance, spherical
power and cylindrical power and axis and optionally object
distance, spherical power and prismatic power and optionally object
distance, and spherical power and cylindrical power and prismatic
power and optionally object distance, wherein each value included
in the individual prescription data is for at least one of far
vision and near vision; and, wherein said providing the spectacle
lens element includes determining the front surface and the rear
surface of the spectacle lens element so as to obtain the spectacle
lens with a base curve with the determined base curve value on the
front surface.
7. The method of claim 6, wherein said determining the base curve
value is done by using a computer implemented method which
calculates the base curve value from the provided individual
prescription data based on a continuous, non-constant functional
relationship between at least one value included in the individual
prescription data and the base curve value.
8. The method of claim 8, wherein at least one of the front surface
and the rear surface of the lens element is machined such that the
spectacle lens in its as-worn position has a dioptric power
according to the individual prescription data.
9. The method of claim 6, wherein said spectacle lens is a
progressive addition lens.
10. The method of claim 9, wherein a progressive surface of the
progressive addition lens is formed on the front surface of the
spectacle lens element.
11. The method of claim 6, wherein the machining of the front
surface includes forming a free-form surface and in which frame
data are provided and the machining of the spectacle lens element
is also based on the frame data.
12. A computer program comprising: a program code stored on a
non-transitory computer readable medium; said program code being
configured to, when the computer program is loaded or executed in a
computer, receive individual prescription data and determine a base
curve value for a front surface of a spectacle lens from the
received individual prescription data; wherein the determining the
base curve value is done by calculating it from the received
individual prescription data based on a continuous, a non-constant
functional relationship between at least one value included in the
individual prescription data and the base curve value, wherein the
at least one value included in the individual prescription data
comprises at least one of: spherical power and object distance,
spherical power and cylindrical power and optionally object
distance, spherical power and cylindrical power and axis and
optionally object distance, spherical power and prismatic power and
optionally object distance, and, spherical power and cylindrical
power and prismatic power and optionally object distance; and,
wherein each value included in the individual prescription data is
for at least one of far vision and near vision.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a computer implemented
method of determining a base curve value representing a base curve
for a spectacle lens, that is, an ophthalmic lens which is worn in
front of the eyeball without being in contact with it. In addition,
the invention relates to a method of manufacturing a spectacle
lens.
BACKGROUND OF THE INVENTION
[0002] A free-form surface of a spectacle lens is a surface which
may freely be formed during the manufacturing process and which
does not need to show axial symmetry or rotational symmetry. In
particular, a free-form surface may lead to different dioptric
powers (spherical and/or astigmatic) in different sections of the
surface. The use of free-form surfaces allows for improving the
quality of spectacle lenses with regard to imaging quality
experienced by the wearer. For example, by use of a free-form
surface a spectacle lens may be optimized in view of the individual
prescription data as well as the individual as worn-position of the
wearer for whom it is manufactured. The possibility of providing a
free-form surface exists for single-vision lenses as well as for
multifocal or progressive-power lenses where the term
"single-vision lens" refers to a spectacle lens designated to
provide a single dioptric power and the term "progressive-power
lens" refers to a spectacle lens with at least one progressive
surface that provides increasing power as the wearer looks down. A
progressive-power lens includes a near portion and a distance
portion where the terms "near portion" and "distance portion" refer
to that portion of the multifocal or progressive-power lens having
the dioptric power for near vision and that portion of a multifocal
or progressive-power lens having the dioptric power for distance
vision, respectively. The difference between the near power and the
distance power experienced by the wearer is called addition power.
Between the near portion and the distance portion there is an
intermediate corridor in which the power experienced by the wearer
decreases from the dioptric power for near vision to the dioptric
power for distance vision and in which the vision for the wearer is
clear. Free-form surfaces of progressive power lenses include a
larger number of parameters, which may be taken into account in the
calculation of the surface than in the calculation of the free-form
surfaces for single vision lenses, for example, the length of the
intermediate corridor, the position of the intermediate corridor or
the addition power.
[0003] A free-form surface may be located at the front surface or
the rear surface of a spectacle lens. However, it is also possible
that both the front surface and the rear surface are free
form-surfaces. In all three cases there usually exists a set of
base curves represented by a base curve value. The base curve value
is given by the nominal surface power typically of the front
surface. In this context, the surface power is the difference
between the refractive index in front and behind the surface
multiplied by the curvature of the surface. If the curvature of the
surface is not constant, as it is for example the case with a
free-form surface, the curvature by which the difference between
the refractive index in front and behind the surface is to be
multiplied resembles a mean curvature at a reference point of the
surface or an average curvature that is averaged over the whole
surface. Often, the base curves are given for a nominal refractive
index of 1.53, even if the material on which the spectacle lens is
made of has another refractive index. In this case, the base curve
value needs to be transformed for the actual refractive index for
optical calculations. The base curve that is to be used for given
prescription data depends at least on the spherical power and/or
the cylindrical power of the spectacle lens. If applicable, the
base curve to be used may depend on further parameters such as
addition power, length of the intermediate corridor, et cetera.
Typically, there exist so-called base curve charts which associate
a number of base curves values to a number of combinations of
spherical power and cylindrical power.
[0004] In case of a free-form surface on the rear surface of the
spectacle lens the front surface is preferably given by a spherical
surface as defined by the base curve value and the shape of the
free-form surface is configured such that the dioptric power
according to the prescription data is provided when the wearer of
the spectacle lens is looking through the spectacle lens.
[0005] In case of a free-form surface on the front surface of the
spectacle lens the focal power resulting from the prescription data
is preferably realized through a suitable spherical or toric shape
of the rear surface of the spectacle lens.
[0006] A main reason for providing a number of base curves is to
provide a meniscus-like shape of the spectacle lenses, that is,
with a convex front surface and a concave rear surface. The concave
rear surface of the spectacle lens shall have preferably a surface
power between at least zero and at least 10 diopter for the whole
rear surface.
[0007] Usually the number of base curves is limited in order to
minimize the number of molds for forming semi-finished lens blanks
and stocking costs. Therefore, typically the number of base curves
is below 10.
[0008] Therefore, each base curve is typically used for a domain of
values of focal powers, where each domain includes intervals of the
values of the different powers, for example, an interval of
spherical power and an interval of cylindrical power. At the
boarders of the domains the base curve values representing the
bending of the front surface show steps which are typically in the
order of one diopter as referred to the refractive index of 1.53.
However, the steps may as well be larger than one diopter, for
example 1.25 or 1.5 diopter.
[0009] There is a desire, to choose the most suitable base curve
for given prescription data and as-worn data. A method of choosing
a suitable base curve out of a set of base curves is described in
U.S. Pat. No. 8,313,194 B2. In this method, a customized base curve
is selected from the list of base curves wherein the customized
base curve is selected according to a customization criterion.
However, with advancing individualization of spectacle lenses
finding suitable base curves is still an issue.
SUMMARY OF THE INVENTION
[0010] An aspect of the invention refers to a computer implemented
method of determining a base curve value. In the description, the
following terms are used as defined below.
[0011] "Spherical power" is a power of a spectacle lens that brings
a paraxial pencil of parallel light to a single focus, where a
paraxial pencil of parallel light is a pencil of light in which the
distance of the light rays contained in the pencil of light from
the optical axis is small and the angles of the rays of light with
respect to the optical axis can be approximated according to sin
.alpha..apprxeq..alpha..
[0012] "Astigmatic power" of a spectacle lens refers to the ability
of a spectacle lens to bringing a paraxial pencil of parallel light
to two separate line foci mutually at right angles. In this
context, the term "principal meridian" refers to one of two
mutually perpendicular meridians of a cylindrical power lens which
are parallel to the two lines of foci where the term "meridian"
refers to a plane which contains the center of curvature of a
surface and the normal-vector at the center of curvature. Related
to the astigmatic power is the "cylindrical power" which stands for
the difference of powers in the two principal meridians. The
direction of the principal meridian which is chosen as reference
for the cylindrical power is called "cylinder axis".
[0013] "Prismatic power" refers to the value of the prismatic
effect at the configured reference point as defined in DIN EN ISO
13666: 2013-10, section 10. DIN EN ISO 13666: 2013-10 is
incorporated herein by reference.
[0014] The term "focal power" is used as a generic term for the
terms "spherical power" and "astigmatic power" and the term
"dioptric power" is used as a generic term for the terms "focal
power" and "prismatic power".
[0015] The term "prescription data" or "individual prescription
data" is used as generic term for a set of optical characteristics
of the spectacle lens like a value for the spherical power, a value
for cylindrical power, a direction of the cylinder axis, and, if
applicable, a value for the addition power as determined by an
ophthalmologist or an optometrist in order to correct the
individual vision of the wearer. In addition, the prescription may
contain further values like, for example, a value for the prismatic
power.
[0016] The term "as-worn position" refers to a position and
orientation of the spectacle lens relative to the eyes and face
during wear (see DIN ISO 13666:2013-10, sections 9.15) and includes
at least values for the back vertex distance, the face form angle
and the pantoscopic angle. The "face form angle" is the angle
between the plane of the spectacle front and the plane of the right
lens shape, or of the left lens shape, the term "pantoscopic angle"
refers to an angle in the vertical plane between the normal to the
first front surface of the spectacle lens at its boxed center, that
is, at the intersection of the horizontal and vertical center
lines, and the term "back vertex distance" refers to the distance
between the apex of the cornea and the rear surface of the
spectacle lens in a defined viewing direction (see DIN ISO
13666:2013-10, sections 5.27 and 17).
[0017] The term "frame data" includes the geometry of the spectacle
frame and the coordinates of the centration point (see DIN ISO
13666:2013-10, section 17).
[0018] The functional relationship is a real function as it is
defined in mathematics. The functional relationship is preferably a
continuous functional relationship.
[0019] A continuous functional relationship means a real continuous
function as it is defined in mathematics: the function f is
continuous at a point h of its domain D, if for every sequence
(x.sub.n) in D, that tends toward h, the sequence F(x.sub.n) always
converges to f(h), that is, f(x.sub.n)->f(h).
[0020] According to a first aspect of the present invention a
computer implemented method of determining a base curve value
representing a base curve for a front surface of a spectacle lens
is provided. The method includes a step of receiving prescription
data, for example, through manual input by use of a human-machine
interface such as a keyboard, a voice recognition unit, a touch
screen, et cetera, or through an electronic interface. From the
received prescription data the base curve value is calculated for
the individual prescription data based on a continuous,
non-constant functional relationship between at least one value
included in the prescription data on the one side and the base
curve value on the other side.
[0021] In an embodiment of the computer implemented method of
determining a base curve value the prescription data comprises at
least a value for spherical power. Alternatively, the computer
implemented method of determining a base curve value comprises at
least a value for spherical power and a value for cylindrical power
or spherical power and object distance, preferably spherical power
and variable object distance, or spherical power and cylindrical
power and optionally object distance or spherical power and
cylindrical power and axis and optionally object distance or
spherical power and prismatic power and optionally object distance
or spherical power and cylindrical power and prismatic power and
optionally object distance, each value included in the individual
prescription data for far vision and/or near vision.
[0022] In this case calculating the base curve value may include
calculating the base curve value based on a functional relationship
between the value for spherical power contained in the prescription
data on the one side and the base curve value on the other side, or
on a functional relationship between values for spherical power and
cylindrical power contained in the prescription data on the one
side and the base curve value on the other side. In this case
possible values for spherical power and cylindrical power which may
be included in the prescription data may form at least two domains
of values. Then, the functional relationship between values
included in the prescription data and the base curve value may
depend on the domain the values for spherical power and cylindrical
power contained in the individual prescription data are part
of.
[0023] In a further embodiment of the computer implemented method
of determining a base curve value the method may further comprise
receiving as-worn position data and/or frame data and taking into
account the received as-worn position data and/or the received
frame data when calculating the base curve value. Like the
individual prescription data the as-worn position data and/or frame
data may be received from manual input through human machine
interface, from an electronic interface, et cetera.
[0024] According to a second aspect of the present invention this
objective is obtained by a method of manufacturing a spectacle
lens, preferably individually adapted to a wearer, where the method
comprises the steps of: [0025] providing individual prescription
data and optionally individual as-worn position data for the
spectacle lens to be manufactured; [0026] determining a base curve
value for the front surface of the spectacle lens element based on
the individual prescription data and optionally based on the
individual as-worn position data; [0027] providing a spectacle lens
element with a front surface and a rear surface; and [0028]
machining the spectacle lens element based on the individual
prescription data and optionally based on the individual as-worn
position data; wherein [0029] determining the base curve value is
done by calculating it from the received individual prescription
data based on a continuous, non-constant functional relationship
between at least one value included in the individual prescription
data and the base curve value, wherein the at least one value
included in the individual prescription data comprises at least
[0030] spherical power and object distance or [0031] spherical
power and cylindrical power and optionally object distance or
[0032] spherical power and cylindrical power and axis and
optionally object distance or [0033] spherical power and prismatic
power and optionally object distance or [0034] spherical power and
cylindrical power and prismatic power and optionally object
distance, each value included in the individual prescription data
for far vision and/or near vision and [0035] providing the
spectacle lens element includes determining the front surface and
the rear surface of the spectacle lens element so as to obtain the
spectacle lens with a base curve with the determined base curve
value on the front surface.
[0036] Individually adapted to a wearer means that the optical
correction of the vision of the wearer is performed by using the
individual prescription data and optionally the data of the as-worn
position.
[0037] According to an aspect of the present invention the
machining of the spectacle lens element includes machining of the
front surface and/or the rear surface of the spectacle lens element
so as to obtain the spectacle lens with a base curve with the
determined base curve value on the front surface.
[0038] According to an embodiment, determining the base curve value
is done by using an inventive computer implemented method of
determining a base curve value.
[0039] In particular, the rear surface of the lens element is
calculated and machined such that the spectacle lens preferably in
its as-worn position has a dioptric power according to the
prescription data.
[0040] The method of manufacturing a spectacle lens individually
adapted to a wearer may, in particular, be applied in manufacturing
spectacle lenses which are progressive addition lenses. In this
case it may be advantageous to form a progressive surface of the
progressive addition lens on the front surface of the spectacle
lens element.
[0041] In an embodiment of the method of manufacturing a spectacle
lens individually adapted to a wearer frame data containing data
about the geometry of the spectacle frame is provided and machining
the spectacle lens element is also based on the frame data.
[0042] According to a third aspect of the present invention, a
computer program is provided with program code for performing the
method steps according to the computer implemented method of
determining a base curve value representing a base curve for a
front surface of a spectacle lens when the computer program is
loaded or executed in a computer.
[0043] The invention provides methods of determining continuous
base curve values as a function of parameters in the prescription
data and to manufacture the respective base curves by machining the
front surface and/or the rear surface of a spectacle lens element
like a spectacle lens blank or a semi-finished spectacle lens
blank. This allows for avoiding steps between the base curve values
related to values contained in the prescription data which differ
only slightly from each other. Using a base curve chart as it is
done in the state of the art may lead to the situation that values,
for example, for spherical power, contained in the prescription
data which differ only slightly from each other lead to different
base curve values which differ by one diopter or more at a
refractive index of 1.53.
[0044] In an embodiment of the invention the minimum curvature of
the rear surface of a spectacle lens element is constant for a
domain of prescription data, for example, a set of combinations of
spherical and cylindrical data, preferably for prescription data
with sphere .gtoreq.0 and the base curve results from the dioptric
requests of the individual prescription data and optionally the
data of the as-worn position and optionally the frame data
resulting in thin, flat and aesthetic spectacle lenses for the
whole domain of individual prescription data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The invention will now be described with reference to the
drawings wherein:
[0046] FIG. 1 shows a flowchart showing how a spectacle lens
individually adapted to a wearer is manufactured;
[0047] FIG. 2 shows a flowchart showing how a base curve for a
spectacle lens is determined;
[0048] FIG. 3 shows a base-curve selection chart according to the
state of the art; and,
[0049] FIG. 4 shows a chart with base curves values calculated
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0050] A detailed description of an embodiment of an inventive
method of manufacturing a spectacle lens individually adapted to a
wearer will be described with reference to the flowchart shown in
FIG. 1.
[0051] In the method, individual prescription data of the wearer as
well as individual as-worn position data of the wearer are provided
in steps M1 and M1'. In addition, frame data are also provided in
step M1''. In the present embodiment, the prescription data
contains values of spherical power and cylindrical power together
with an indication of the direction of the cylinder axis, where the
values of spherical power and cylindrical power may also include
zero so that the spectacle lens resulting from an inventive method
may have a spherical power of 0 diopter or an cylindrical power of
0 diopter. However, in the general case the prescription data
contains a non-zero value for spherical power and a non-zero value
for cylindrical power. In addition to the values for spherical
power and cylindrical power the prescription data may contain
additional values, i.a. a value for representing addition power
and/or a value representing prismatic power. The as-worn position
data contains in the present embodiment a value for the back vertex
distance, a value for the pantoscopic angle and a value for the
face form angle and the frame data contains data relating to the
geometry of the spectacle frame.
[0052] In a next step M2 a base curve value representing a base
curve for the spectacle lens to be manufactured is determined. The
base curve value is a measure for the nominal surface power to be
given to the front surface of the spectacle lens. According to the
embodiment, the base curve value--and thus the base curve, is
determined based on the combination of values given in the
prescription data and, if applicable, in the as-worn position data
and/or in the frame data. How the base curve value is determined
will be described later with respect to the flowchart of FIG. 2.
The nominal surface power of the front surface does not need to be
the exact final surface power of the front surface if the free-form
surface is formed on the front surface.
[0053] Next, in step M3 the shapes of the front and rear surfaces
of the spectacle lens are determined. In the present embodiment, a
free-form surface is to be formed on the front surface. In this
case, a suitable spherical or toric rear surface is determined such
that the free-form surface on the front surface has an average
curvature, that is, a curvature averaged over the whole surface, or
a mean curvature at a reference point of the front surface, which
leads to a surface power that approximately matches the base curve
value. Determining the spherical or toric rear surface typically is
done iteratively by means of ray tracing. In the ray tracing
process, a starting geometry of the spectacle lens is given. The
starting geometry may include as front surface a known free-form
front surface or a spherical front surface, which has the required
base curve value, and as rear surface a given spherical or toric
surface. Then, the spherical or toric rear surface is varied until
the calculated power of the spectacle lens coincides with the
required power for correcting the ametropia of the wearer,
preferably with the spectacle lens being in the as-worn
position.
[0054] With the so determined spherical or toric rear surface the
free-form surface is optimized using ray-tracing. During this
optimization, the average curvature or mean curvature,
respectively, does not change significantly anymore, so that the
front surface keeps the required base curve value.
[0055] Next, in step M4 a lens element is provided which has a
front surface and a rear surface. The lens element may be a
spectacle lens blank or a semi-finished spectacle lens blank. In a
semi-finished spectacle lens blank the front surface usually has
one of a number of surface powers which may be chosen such that the
surface power of the front surface corresponds to the determined
base curve value as closely as possible. However, it is not
mandatory to provide a semi-finished spectacle lens blank with a
surface power of its front surface which corresponds to the base
curve value. In particular, instead of a semi-finished spectacle
lens blank a spectacle lens blank with flat front and rear
surfaces, that is, a cylindrical spectacle lens blank, may be used
as well. The only restriction is, that the spectacle lens blank
needs to be thick enough to allow manufacturing the spectacle lens
with the determined base curve.
[0056] Once the base curve value is determined, the shapes of the
front and rear surfaces of the spectacle lens are determined and
the spectacle lens element is provided, the spectacle lens element
is machined in step M5 based on the prescription data and the
as-worn position data so as to form a front surface and a rear
surface having the determined shapes, such that a spectacle lens is
formed that is individually adapted to the wearer. Machining the
spectacle lens element includes for example machining the front
surface so as to form the base curve represented by the determined
base curve value on the front surface. In case the spectacle lens
to be manufactured is a single vision lens or a progressive power
lens with the free-form surface formed on the rear surface the rear
surface will be machined according to the prescription data so as
to form a rear surface which together with the front surface allows
the spectacle lens to fulfill the individual optical needs given in
the prescription data.
[0057] If, on the other hand, the spectacle lens is a progressive
addition lens with the free-form surface formed on the front
surface the front surface is machined according to numerical data
describing the free-form surface. This numerical data is based on
the individualized power to be achieved and optionally on the
as-worn position. It is also possible to form in addition to the
free-form surface on the front surface a further free-form surface
on the rear surface. Then both free-form surfaces together provide
for the addition power of the progressive addition lens.
[0058] The machining performed in step M4 may include milling and
polishing the front surface and/or the rear surface under computer
numeric control for producing the free-form surface and fine
turning on which follows a polishing step. After the lens has been
machined one or more coatings may be applied on one or more of the
spectacle lens surfaces.
[0059] FIG. 2 shows the method of determining a base curve value
for the spectacle lens. In the present embodiment, the method is
implemented on a computer and comprises the step of receiving
prescription data (step D1) through a computer interface. In
addition, an optional step of receiving as-worn position data (step
D1') through the computer interface and/or an optional step of
receiving frame data (step D1'') with data relating to the geometry
of the spectacle frame through the computer interface may be
present.
[0060] Next, in step D21 the program evaluates the values contained
in the prescription data to see whether these values belong to one
of a number of domains the values in the prescription data may be
in. In the present embodiment, the base curve value is determined
based on the values of spherical power and cylindrical power given
in the prescription data. The spherical power may assume values
between -8 diopter and +7 diopter and the cylindrical power may
assume values between 0 and +4 diopter. A first domain of values of
the prescription data contains, in the present embodiment, all
combinations of values for spherical power and cylindrical power in
which the spherical power is below -7 diopter. If it is determined
in step D21 that the value for spherical power given in the
prescription data is below -7 the method proceeds to step D31 in
which a functional relationship between the spherical power on the
one side and the base curve value on the other side is applied to
determine the base curve value from the value of the spherical
power. The functional relationship used in step D31 is valid for
all values of the prescription data which are in the first
domain.
[0061] If, on the other hand, it is determined in step D21 that the
value for the spherical power is not below -7 the method proceeds
to step D22 in which it is determined whether the combination of
the value for spherical power and the value for cylindrical power
given in the prescription data is in the second domain. The second
domain contains all combinations of values for spherical power and
cylindrical power in which the value for spherical power is between
-7 and -4.75. In case of Yes, the method proceeds to step D32 in
which a second functional relationship is applied which relates the
value of the spherical power to the base curve value. In case the
spherical power is not in the interval between -7 diopter and -4.75
diopter the method proceeds to a further step in which it is
determined whether the values given in the prescription data lie in
a third domain. This proceeds until all n domains have been checked
and the values given in the prescription data have been associated
to one of the domains. In other words, the method determines to
which domain the values the combination of spherical power and
cylindrical power given in the prescription data belongs and
applies the corresponding functional relationships between the
value spherical power and the base curve value or between the
spherical power and the cylindrical power and the base curve value.
At the end, the determined base curve value is output in step
D4.
[0062] An example for a program code by which the domain the
combination of spherical power and cylindrical power given in the
prescription data belongs to and the base curve value can be
determined based on the values of spherical power and cylindrical
power given in the prescription data is, for example
TABLE-US-00001 if (fSph < -7.00) then fGK =
1.00+(8.00+fSph)*0.40/1.00 elseif (fSph < -4.75) then fGK =
1.40+(7.00+fSph)*0.90/2.25 elseif (fSph < -3.00) then fGK =
2.30+(4.75+fSph)*0.90/1.75 elseif ((fSph < -1.50).and.(fSph+fZyl
< 1.50)) then fGK = 3.20+(3.00+fSph)*0.80/1.50 if (fSph+fZyl
> 1.00) fGK = fGK+.30*(fZyl-3.00) elseif (fSph+fZyl < 1.50)
then fGK = 4.00 elseif ((fSph+fZyl < 4.50)) then fGK =
4.00+(fSph+fZyl-1.50)*2.50/3.00 else fGK =
6.50+(fSph+fZyl-4.50)*1.00/2.50 endif
where fGK stands for the base curve value in diopter, fSph stands
for the value of the spherical power in diopter of the prescription
data and fZyl stands for the cylindrical power in diopter of the
prescription data.
[0063] FIG. 3 shows a base curve chart according to the state of
the art showing base curve values for combinations of spherical
power and cylindrical power with the spherical power being in the
range of -8 to +7 diopter and the cylindrical power being in the
range of 0 to 4 diopter. FIG. 4 shows for the same combinations of
values for spherical power and cylindrical power the base curve
values determined by use of the above program code. The base curve
values provided in FIGS. 3 and 4 are based on the organic material
with a refractive index of 1.50, for example, poly(allyl diglycol
carbonate) also known as CR39.
[0064] As can be seen from FIG. 3, in the state of the art base
curve chart there are steps between neighboring values of spherical
power and/or cylindrical power which are one diopter or more at a
refractive index of 1.53. For example, in the base curve chart
shown in FIG. 3 the base curve value for a spherical power of 1.25
diopter and a cylindrical power of 0.50 diopter would be 5.25
diopter whereas the base curve value for a spherical power of 1.00
diopter and a cylindrical power of 0.50 diopter would be 4.00
diopter. This means a step of 1.25 diopter is present between the
spherical power of 1.00 diopter and 1.25 diopter. If, for example,
the left and right lenses of a spectacle have spherical powers of
1.00 diopter and 1.25 diopter, respectively, and both have a
cylindrical power of 0.50 diopter the base curve chart of the state
of the art would lead to a situation where the left spectacle lens
would have a base curve value of 4.00 diopter and the right
spectacle lens would have a base curve value of 5.25 diopter. In
other words, the left and right spectacle lenses would look rather
different although the difference in spherical power is rather
small. In the chart showing the base curve values as calculated by
the above program code the differences in the base curve values of
neighboring values of spherical power and/or neighboring values of
cylindrical power are always small. For example, for the
prescription data with a value of 1.25 diopter for the spherical
power and a value of 0.5 diopter for the cylindrical power, a
method according to the invention provides a base curve value of
4.21 diopter, and for a value of 1.00 diopter for the spherical
power and a value of 0.50 diopter for the cylindrical power the
inventive method provides a base curve value of 4.00 diopter (see
FIG. 4). Hence the difference is only 0.21 diopter as compared to
1.25 diopter in the state of the art base curve chart. Such a small
difference is barely visible in the finished spectacle lenses.
Hence, the invention allows for producing more aesthetic
spectacles.
[0065] In general, aesthetic reasons lead to the desire to have the
base curve for higher positive spherical powers as flat as
possible. With the inventive method flatter base curves can be
achieved. For example, assume a spherical power of 4.00 diopter
with a cylindrical power of 0.75 diopter. According to the state of
the art base curve chart shown in FIG. 3 this would lead to a base
curve of 8.00 diopter. According to an inventive method a base
curve of 6.60 would be sufficient. Furthermore, sometimes spectacle
glasses with a desired base curve are ordered. If, for example a
spectacle lens is ordered with a spherical power of 3.25 diopter
and a cylindrical power of 0 diopter with a desired base curve of
5.5 diopter the state of the art base curve chart of FIG. 3 would
lead to a base curve of 6.5 diopter since the base curve of 5.25
diopter would already be to flat for producing the spectacle lens.
With the inventive method, a base curve of 5.46 diopter would be
provided which matches the desired base curve very closely.
[0066] With the inventive method a base curve chart with not
normalized values (for example not normalized to a step size of
0.25 diopter) may also be generated.
[0067] In the chart of FIG. 4 the spherical power and the
cylindrical power are given in steps of 0.25 diopter for comparing
it with the base curve chart of FIG. 3. However, the values of
spherical power and/or cylindrical power may be given in a
continuous fashion or in much smaller steps than shown in the chart
of FIG. 4. Of course determining the base curve value may also be
done in the same way for values of spherical power and/or
cylindrical power that are given in steps that are smaller than
0.25 diopter, for example for values that are given in steps of
0.01 diopter, or even less.
[0068] Furthermore, the method offers the possibility to adapt the
base curve on the front surface in an optimal fashion to the
prescription data, the as-worn position and the data of the
spectacle frame. In particular, orders for positive spherical power
and positive cylindrical power often contain very flat base curves
for aesthetic reasons. The requirements of the bending of the rear
surface (for example given through a minimum value) may include the
absolute surface power of the rear surface over the whole surface
or almost the whole rear surface or a minimum value for the average
curvature of the rear surface, that leads to a minimum bending,
that is, a minimum base curve value of the front surface. Starting
from the requirements of the bending of the rear surface can be
determined such that the finished spectacle lens realizes the
desired spherical and cylindrical power, the required bending of
the rear surface and optionally the as-worn position. In this
context the data of the spectacle frame influences a glass
thickness of the spectacle lenses and thereby also the curvature
required for the front surface and the rear surface. Hence, the
invention allows for taking the frame data into account. The base
curves values can then not be represented by a chart as shown in
FIG. 4 because the base curve values also depend on the individual
as-worn position and the data of the spectacle frame. However, in
any case a suitable base curve can be calculated through a
functional relationship taking into account not only spherical
power and/or cylindrical power but also values of the as-worn
position and of the frame data. In the end the wearer receives an
aesthetically optimized spectacle glass which only leads to a small
magnification or small diminution of the visual perception of the
eyes behind the spectacle lens.
[0069] The present invention has been described by use of specific
embodiments of the invention for illustrative reasons only. A
person skilled in the art is aware of possible deviations from the
embodiments. For example, although eight functional relationships
are used in the program code shown with respect to the present
embodiment a larger or smaller number of functional relationships
could be used where the larger or smaller number of functional
relationships comes along with a larger or smaller number of
domains for the values given in the prescription data. Moreover,
FIGS. 1 and 2 show the prescription data, the as-worn position data
and the frame data to be provided/received simultaneously. However,
it would also be possible to provide/receive these data serially in
any possible order.
[0070] It is understood that the foregoing description is that of
the preferred embodiments of the invention and that various changes
and modifications may be made thereto without departing from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *