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.

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

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 valueand 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*(fZyl3.00) elseif (fSph+fZyl < 1.50) then fGK = 4.00 elseif ((fSph+fZyl < 4.50)) then fGK = 4.00+(fSph+fZyl1.50)*2.50/3.00 else fGK = 6.50+(fSph+fZyl4.50)*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.