WO2007126316A1

WO2007126316A1 - Method and devices for manufacturing an opthalmic lens

Info

Publication number: WO2007126316A1
Application number: PCT/NL2007/050195
Authority: WO
Inventors: Jakob Leonard Broers
Original assignee: Htp Tooling B.V.
Priority date: 2006-05-03
Filing date: 2007-05-03
Publication date: 2007-11-08

Abstract

A method for manufacturing finished progressive ophthalmic lenses by means of injection molding. The method includes providing a mold insert corresponding to the progressive front surface of the lens and providing a mold insert corresponding to the back surface of the lens with the cylinder, aligning the mold inserts so that the optical centers of the mold inserts coincide with the normal to the optical center of either the mold insert, rotating the mold insert about the normal that coincides with both optical centers to obtain the required correlation between the cylinder angle and the direction of the progressive surface.

Description

Method and devices for manufacturing an ophthalmic lens

The present invention relates to ophthalmic lenses, in particular to progressive lenses with a progressive surface and a torical or atorical surface, and to a method of designing such lenses. Further, the invention also relates to a method for manufacturing a progressive lens by injection molding, and relates to mold inserts for use in manufacturing such lenses.

Progressive lenses are presently manufactured by keeping a larger number of semi finished blanks with different geometries in stock, and finishing the blanks individually to meet the prescription, e.g. by polishing.

However, pricing and flexible fast delivery are important competitiveness factors. Keeping a large variety of semi-finished blanks on stock is expensive. The process of finishing semi finished blanks is labor intensive.

Single vision finished ophthalmic lenses are hereto often made in polycarbonate by injection molding. The power of the single vision finished lens is accomplished by the use of two mold inserts, a back insert and a front insert. The difference between the radii of the inserts produces the basic power of the lens. The power of an ophthalmic lens is graded in steps of 0.25 dioptres.

The human eye often needs a cylinder correction. This means that two different powers in perpendicular directions are needed to correct the astigmatism in the eye. The cylinder correction ranges 0 to 180 degrees along the horizontal line of the eye, but for practical reasons the prescriptions are divided in steps of 5 or 10 degrees, which are sufficiently small steps to comply with the standards in ophthalmics. The angle of the cylinder is positioned when the frame curve of the spectacle is cut into the blank (Edging). The ophthalmic world uses the basic (mean) power and the cylinder for the prescription to fit the lens to the eye for correction. The most common 75% of the prescriptions include approximatly 392 variations. In single vision finished ophthalmic lenses made by injection molding the 392 prescriptions are created by for example using 4 front curve inserts and per prescription one of 175 different back curve inserts which cover various base curves and cylinder values. In a progressive lens power increases smoothly from the distance vision area at the top of the lens through an intermediate vision area in the middle, to the near vision area at the bottom of the lens. Typically, the progression is formed in the front surface of the lens, whilst the cylinder is formed in the back surface. Since the front surface is not rotation- symmetric, and since the orientation of the front surface relative to the patients eyes is fixed, it is not possible to position the angle of the cylinder when the frame curve of the spectacle lens is cut into the blank. The added power zone would namely not be at the right location. The progressive lens design is also mirrored for the left and right eye.

This means that there is a much greater variation in lens geometry for a finished progressive added or multifocal lens to cover the range of possible prescriptions. There are 18 (36) different prescriptions for the cylinder angle. Relative to a single focus lens reading powers of 0.5 diopter to 3.5 diopter are added to the basic power of the lens.

In order to cover the most common 175 prescriptions that form about 75% of the total volume of prescribed lenses a huge number of variations in lens geometry need to be produced:

175 prescriptions for power and cylinder 175x13 including added powers for reading 175x13x18 including different cylinder angles. 175x13x18x2 for both left and right lenses. Makes: 81.900 or 40.950 pairs (left and right)

If for every prescription 10 pairs of lenses are kept in stock, the stock will comprise 409.500 pairs. At a cost price of 10 Euro per pair the stock value will be 4.095.000, — Euro. This is not an economically viable type of stock, and therefore semi finished blanks are finished individually. If finished progressive lenses were to be molded on an injection machine, the amount of inserts for creating these prescriptions is 227, not taking into account the different cylinder angles. This number is based on the use of front inserts for 2 base curves with each 13 added powers times 2 for left and right plus 175 different prescriptions for the back inserts. These 227 different mold inserts are required for covering all variations in diopter and progressiveness. If for every one of the 18 (or 36) cylinder angle a different back insert is needed, more than 3000 inserts have to be made to be able to produce 75% of all prescriptions needed. Such a large number of inserts is too costly and unmanageable to be used in a manufacturing process that can compete on the market. Further, this number does not take into account the need for tilting the one lens surface relative to the other in order to achieve the optimum balance between edge thickness reduction and prism. To accommodate this aspect of the lens geometry the amount of required mold inserted would need to be multiplied by another factor, thus making it up to now practically impossible to manufacture progressive finished lenses on an injection molding machine.

It would be desirable to manufacture finished progressive lenses in one step with an injection molding machine.

This object can be achieved with a ophthalmic lens with a front and a back surface, one of which is progressive and the other is torical or atorical, which surfaces having a geometry that matches a given diopter value, a given cylinder value and a given cylinder angle, whereby the optical center of the front surface is aligned with the optical center of the back surface. This new ophthalmic lens and the molds necessary for injection molding this new ophthalmic lens can be designed and manufactured easily as will be apparent from the methods according to the present invention as described below.

The object is also achieved by providing a method for designing an ophthalmic lens with a front and a back surface, one of which is progressive and the other is torical or atorical, the lens requiring a given diopter value, a given cylinder value and a given cylinder angle, the method comprising determining a combination of a progressive front surface geometry and an atoric or toric back surface geometry that matches the given diopter value and given cylinder value, aligning the optical center of the front surface with the optical center of the back surface by shifting the front surface relative to the back surface until the optical axis of the front surface substantially coincides with the optical center of the back surface or until the optical axis of the back surface coincides with the optical center of the front surface.

This method for designing an ophthalmic lens according to the present invention is in fact a method of addapting excisting or new progressive designs for creating an ophthalmic lens with a progressive front surface and a torical or atorical back surface.

By aligning the optical centers of the front and back surfaces of the lens, it becomes possible to rotate the back surface relative to the front surface without introducing errors in the lens geometry. By enabling a rotation between the front and back surface, it becomes possible to design lenses with various cylinder angles without the need for complicated additional measures. The method may also include tilting the back surface and/or the front surface about their/its optical center to optimize the balance between reduction of distance variation between the edges of the front surface and the back surface and wanted or allowed prism effect of a resulting lens. The method may further comprise adjusting the distance between the front surface and the back surface to obtain a given value for the minimum distance between the edges of the front surface and the back surface. Thus, it becomes possible to set the minimum lens thickness at the periphery in advance, and to optimize the lens thickness at the edge and in the center by moving the front surface and the back surface closer to one another until the minimum edge thickness (or center thickness) reaches the predetermined value. Thus, lenses that are overall thinner and optically more attractive can be created.

Normally, the finished lens has to have a given diameter before it is cut to match the contour of the spectacle frame in which it is to be used. The method may therefore comprise the step of selecting the diameter of the front surface and of the back surface to compensate for reduction in lens diameter caused by the shift of the front surface relative to the back surface. The given diameter for lenses is standardized and 76 mm is a typical value for the diameter of finished lenses. In the prior art methods, the lenses were designed with a front surface and a back surface that have a diameter corresponding to the required diameter of the finished lens. In order to obtain this lens diameter with the surface shift that is applied in the present invention to align the optical centers, an enlarged diameter for the front and back surfaces is used to obtain an overlap diameter, so that the effective lens diameter is at least equal to or exceeds the required diameter of the finished lens.

The method may further comprise the step of rotating the back surface about its optical axis. Thereby, the required cylinder angle can easily be obtained. The front surface may either be progressive or aspherical progressive.

Preferably, the front or back surface is tilted about its optical center, whilst the opposite surface is not tilted about its optical center. The tilt of the front and/or back surface is necessary to be able to optimize the lens so that the optimium balance of prism and edge thickness reduction of the lens is achieved. In conventionally designed progressive lenses, it has always been the relatively complicated progressive front surface that had been decided upon first at the start of the design process, thereby determining one of the base curves and the strength of the progressiveness. Thereafter, all the other adaptations of the lens to fulfill the prescription requirements were carried out by modifications to the back surface, whereas the front surface was not touched upon. Thus, it has always been the back surface that was adapted during finishing on a grinding/polishing machine in order to achive the optimum balance between prism and edge thickness reduction. This practice has created a prejudice in the art that it is the back surface that adapted to optimize the lens. However, the inventors of the present invention arrived at the insight that there would be a great advantage applying tilt to the progressive front surface, because this would lead to a further reduction in the number of mold inserts that are required to cover various prescriptions. This is caused by the fact that the progressive design of the front surface determines the distance between the optical center and the geometrical center of the front surface. This difference in combination with the strength of the base curve determines the tilt angle that is required to optimize the lens for edge thickness and prism. Thus, only one tilt angle is optimal for a specific progressive front surface when the tilt is performed about the optical center of the front surface. In contrast hereto, a large number of different tilt angles need to be combined with various base curves and cylinder values of the back surface when the tilt is performed about the optical center of the back surface. Thus, the insight that it is the front surface that should be tilted about its optical center simplifies the injection molding process and greatly reduces the amount of different mold inserts required to cover a large variety of prescriptions.

The method may also be used to manufacture exchangeable mold inserts with surfaces corresponding to the designed lenses.

The object is also achieved by providing a method for manufacturing a finished progressive ophthalmic lens with a given diopter value, a given cylinder value and a given cylinder angle on an injection molding machine with at least two mold halves, comprising providing a first mold insert with a surface with a contour corresponding to the front surface of the lens to be manufactured, providing a second mold insert with a surface with a contour corresponding to the back surface of the lens to be manufactured, placing the first mold insert in one of the mold halves, placing the second mold insert in the other mold half with the position on the surface of the second mold insert that corresponds to the optical center of the back surface of the lens and the position on the surface of the first mold insert that corresponds to the optical center of the front surface of the lens substantially coinciding with the normal to the optical center of the front surface or with the normal to the optical center of the back surface.

By aligning the mold inserts in the molding machine, it becomes possible to rotate one of the mold inserts relative to the other one about the optical axis of the lens surface that it corresponds to. Thus, it becomes possible to create a lens with a rotational direction specific progressive contour in the front surface and a rotational direction specific cylindrical contour in the back surface with the correct relation between the cylinder angle and the progressive surface in an injection molding machine without the need for an enormous amount of different mold inserts. Since the standardized prescriptions for ophthalmic lenses cover 18 (36° for 5 increments of the cylinder angle) different cylinder angles, the amount of inserts required for being able to cover spectrum of prescribable lenses is reduced by a factor 19. This means that the amount of mold inserts that is required to cover 75% of all prescriptions is reduced from approximately 3200 to 168 (from 6400 to 168 for 5° increments).

Ideally, the prescriptions for the cylinder angle are made by increments of only 5°, in order to match the characteristics of the lens better to be astigmatism over the eye, which is of course only very rarely exactly 10°, 20° or other multiple of 10°. With 5° increments the number of possible cylinder angles rises from 18 to 36, and in this case the reduction in the required amount of mold inserts is a factor 36.

Preferably, the method further comprises rotating one of the mold inserts about an axis that substantially coincides with the normal to the optical center of the lens surface that it corresponds to for obtaining the required cylinder angle for the lens. Thus, all that is needed for obtaining a different cylinder angle is a simple rotation of a mold insert.

The method may further comprise providing a plurality of first mould inserts with various geometries, providing a plurality of second mould inserts with various geometries, and selecting a combination of a first mold insert and a second mold insert that results in the required diopter value, cylinder value and progressiveness. Thus, the various diopter values, cylinder values and progressiveness levels can be easily changed by selecting the appropriate combination of front and back mold insert.

The method may further comprise disposing the progressive surface of the lens on either the front surface or back surface of the lens, and shifting the optical center of the mold insert surface that corresponds to the progressive lens surface to coincide with the geometrical center of the mold insert concerned. By arranging the optical center in the geometrical center of the mold insert it is possible to simply rotate a mold insert with a circular outer contour inside the cylindrical mold half. Progressive lenses are up to now usually made by selecting a front surface as a starting point, where after any variations in the lens prescription are made by changing characteristics of the back surface. Thus, blanks were manufactured with a selected front surface, whereas the back surface was finished in order to meet the prescription, for example by grinding/polishing the required cylinder angle into the back of the lens. The required adaptation of the back surface relative to the front surface has up to now also been done by grinding/polishing the back surface. Therefore, it is a general design practice in this field to first select the front surface, whereafter all modifications to the lens are made in the back surface. This has led to a prejudice in the art that lens finishing is usually done by modifications to the back surface. This means that an enormous amount of different mold inserts for the back surface will be required to manufacture a finished progressive lens on an injection molding machine, since the mold inserts for the back surface will need to cover a variety of cylinder angles and a variety of tilt angles, which are for the back surface independent variables, so that a plurality of mold inserts with various tilt angles will have to be provided for each cylinder angle, i.e. the tilt angle adjustments multiplies the number of different back surface mold inserts by another factor. The resulting vast number of different mold inserts has up to now prevented production of progressive lenses on injection molding machines.

However, the inventors of the present invention arrived at the insight that it would be a great advantage to apply the required amount of tilt to the front surface when manufacturing a finished lens in an injection molding machine. The required amount of tilt of the normal to the optical center of the front surface is namely defined by a combination of the shift that was made for aligning the optical center of the front surface with the optical center of the back surface with the progressiveness of the front surface of the lens. The inventors realized that the tilt angle is therefore completely defined by the characteristics of the front surface. Thus, only one tilt angle is associated with a specific front surface configuration. Thus, there needs to be only one front insert for each configuration of the front surface with the correct inbuilt tilt angle to achieve an optimized balance between prism and edge thickness reduction when manufacturing progressive lenses on injection molding machine. Thus, when the tilt is realized in the mold inserts for the front surface, i.e. the angle is built into the mold insert by placing the normal to the optical center of the front surface at an angle with the axial axis of the mold insert, the required number of mold inserts necessary to manufacture progressive lenses on an injection molding machine is greatly reduced. The most optimized combination of allowed lens prism and minimized variation in thickness between the edge of the front surface and the edge of the back surface can be realized by constructing the mold insert for the front surface such that the normal to the optical center is in the correct direction. Preferably, the progressive surface of the lens is the front surface and the cylinder is formed in the back surface. The object above is also achieved by providing a set of exchangeable mold inserts for use in an injection molding machine to manufacture progressive ophthalmic lenses, the set comprising a plurality of first mold inserts with a mold surface corresponding to the front surface of a lens to be produced, a plurality of second mold inserts with a mold surface corresponding to the back surface of a lens to be produced, the first and/or second mold inserts being provided with a surface that corresponds to a progressive lens surface in which the geometrical center does not coincide with the optical centre, and wherein the mold surfaces on the first mold inserts and the mold surfaces on the second mold inserts are disposed such that the normal to optical center of the lens surface corresponding to the mold surface of the first mold insert substantially coincides with the optical center of the lens surface corresponding to the mold surface of the second mold insert or are disposed such that the normal to optical center of the lens surface corresponding to the mold surface of the second mold insert substantially coincides with the optical center of the lens surface corresponding to the mold surface of the first mold insert when a pair of a first mold insert and a second mold insert is inserted in the molding machine.

By providing mold inserts that automatically align the optical centers of the lens surfaces that they represent, it becomes possible to manufacture progressive finished lenses on an injection molding machine.

The object above is also achieved by providing a set of exchangeable mold inserts for use in an injection molding machine to manufacture progressive ophthalmic lenses, the set comprising at least one first mold insert with a mold surface corresponding to a progressive front or back surface of a lens to be produced, at least one second mold insert with a mold surface corresponding to the front or back surface opposite to the progressive surface of a lens to be produced, wherein the mold surface of the first mold insert is tilted about the optical center of the lens surface to which the mold surface corresponds, so that the normal to the lens surface to which the mold surface of the first mold insert corresponds is at an angle with the normal to the lens surface to which the mold surface of the second mold insert corresponds in order to optimize the variation in edge thickness in combination with prism effects of the lens to be produced. Preferably, the set of exchangeable mold inserts includes mold inserts that have substantially cylindrical bodies and wherein the normal to the optical center of the lens surface to which the mold surface of the second mold insert corresponds substantially coincides with axial axis of the body of the second mold insert, and the normal to the optical center of the lens surface to which the mold surface of the first mold insert corresponds is not parallel with the axial axis of the body of the first mold insert.

The optical centre of the surface to which the first mold insert corresponds may coincide with the axial axis of the body of the first mold insert. The object above is also achieved by providing a mold insert for use in an injection molding machine to manufacture progressive ophthalmic lenses, the mold insert being provided with a mold surface corresponding to the front surface or to the back surface of the lens to be manufactured, the mold insert being provided with means for selectively presetting the angular position of the mold insert concerned as measured about the optical axis of the lens surface corresponding to the mold surface of the insert relative to the molding machine.

Thus, a progressive lens with a cylinder value and cylinder angle can be flexibly produced an injection molding machine, since it has become easy to quickly set the correct angle between the progressive lens surface and the cylinder carrying surface between individually designed lenses.

Preferably, the means for selectively setting the angular position of the mold insert comprise a mold engaging member that is rotably suspended from the mold insert about an axis that substantially coincides with the optical axis of the lens surface to which the mold surface corresponds. Thus, a simple rotation around the axes of the mold engaging member is enough to change the cylinder angle of the lens to be produced.

The mold insert may further comprise means to controllably cause friction between the mold engaging member and the mold insert to avoid inadverted rotational movement of the mold engaging member relative to the mold insert.

The injection molding machine may be of the type that includes 2,4,8 or any other number of pairs of mold insert and corresponding numbers of mold cavities in the mold.

The object above is also achieved by providing a method for manufacturing ophthalmic lenses on an injection molding machine between a first exchangeable insert with a mold surface with a contour corresponding to the front surface of the lens to be manufactured and a second exchangeable insert with a mold surface with a contour corresponding to the back surface of the lens to be manufactured, comprising providing a plurality of first mold inserts with a variety of different surface contours, providing a plurality of second mold inserts with a variety of different surface contours, preheating a first and/or second mold insert that have surfaces that correspond to a lens to be manufactured during one of the next molding cycles, exchanging the first and/or second mold inserts in the molding machine with preheated first and/or second mold inserts, and molding the individually contoured lens to be manufactured.

By providing preheated lens inserts, it becomes possible to keep short run up time. After a mold insert change the molding run can start almost immediately because the mold inserts do not need to be heated up inside the molding machine.

Preferably, the method comprises providing an auxiliary tool for preheating the mold inserts. By providing an auxiliary tool for preheating the mold inserts, it becomes possible to heat up a mold insert for a next cycle in a relatively short period of time. Preferably, the method comprises providing an auxiliary tool with means for setting the rotational position of a mold insert relative to the mould halves, the rotational position being measured around the optical axis of the lens surface that corresponds to the surface of the mold insert. Thus, the rotational position can be set in advance and this setting process does therefore not delay the injection cycle. Preferably the step of exchanging the first and/or second mold inserts in a molding machine comprises the step of inserting the first or second mold insert into a half of a jacket, comprising: connecting the mold insert to a free end of an extended piston rod of a piston, and retracting the piston rod whereby the mold insert is retracted into a jacket. The procedure for removing a mold insert from the mold is the reverse of the procedure to insert a mold insert into the mold and is caused by the piston to expel the mold insert, preferably by pressure applied via the piston rod. In this way exchanging a mold insert with another one is easily and can be carried out quickly. This is advantageous for the method according to the present invention because in this method it is necessary to exchange the mold inserts often.

To achieve that the new mold insert is placed in the correct position the piston rod is further retracted until a rear surface of the mold insert abuts with a base of the jacket and a pin that protrudes from the rear surface of the mold insert near the periphery thereof engages one of a plurality of holes arranged as a semicircular array in the base of the jacket.

It is noticed that the method of exchanging the mold inserts can not only be used in a method for manufacturing finished progressive lenses, but also in a method for manufacturing any other kind of finished lenses.

The object above is also achieved by providing an auxiliary tool for adjusting the preset angular position of the mold insert according to any of claims 25 to 29 relative to the mold of the molding machine in which said mold insert is to be placed. The tool may comprise means for engaging the connection member of the mold insert and means for indicating the angular position of said connection member relative to the mold insert.

The object above is also achieved by providing an auxiliary tool for preheating mold inserts that are provided with a molding surface that corresponds to the front surface or to the back surface of an ophthalmic lens.

Preferably, the auxiliary tool comprises a housing with one or more cylindrical recesses for receiving said mold inserts therein.

Instead of adjusting the angular position of the mold insert relative to the mold in which said mold insert is to be placed, it is also possible to adjust the angular position of the mold insert relative to the mold when said mold insert is already placed in the mold.

Further objects, features, advantages and properties of the progressive lens, plurality of mold inserts and method of designing an ophthalmic lens according to the invention will become apparent from the detailed description.

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which: Fig. IA is a cross-sectional view through a front surface and a back surface of a lens along the 0-180° meridian, to illustrate a shift between the two surfaces,

Fig. 1 is a cross-sectional view through a front surface and a back surface of a lens along the 0-180° meridian,

Fig. 2 is a cross-sectional view through a front surface and a back surface of Fig. 1 along the 90-270° meridian,

Fig. 3 is a cross-sectional view through a front surface and a back surface of a lens along the 0-180° meridian, after a tilt between the front surface relative to the back surface,

Fig. 4 is a cross-sectional view through a front surface and a back surface of Fig. 3 along the 90-270° meridian,

Fig. 5 is a cross-sectional view through a first mold insert and a second mold insert for producing a lens with surfaces as shown in Fig. 1 to 4 along the 0-180° meridian,

Fig. 6 is a cross-sectional view of the mold inserts shown in Fig. 5 along the 90-270° meridian, Fig. 7 is a cross-sectional view through the mold inserts of Figs. 5 and 6 to illustrate a rotation of the second mold insert relative to the first mold insert,

Figs. 8 and 9 illustrates different cross-sectional views through the mold inserts of Fig. 6 after a rotation of one of the mold inserts, Figs. 10 and 11 illustrates the same cross-sectional views as Figs. 8 and 9 with a different angle of rotation of one of the mold inserts,

Fig. 12 illustrates a lens according to an embodiment of the invention,

Fig. 13 is a cross-sectional view through a mold for use with the present invention, with mold inserts according to the present invention Fig. 14 is a detail of Fig. 13,

Fig. 15 is a further enlarged detail of Fig. 14,

Fig. 16 is a perspective on a mold insert according to the present invention,

Figs. 17 through 19 illustrate the process of inserting a mold insert according to the invention into a mold, Figs. 2OA and 2OB illustrate an auxiliary device according to the invention for adjusting the angular position of mold inserts prior to placing the mold inserts into a mold,

Figs. 21 is a top view on an auxiliary device according to the invention for preheating mold inserts according to the invention, and

Fig. 22 is a side view on the device of Fig. 21.

Figs. IA, and 1 to 4 illustrate a method according to a preferred embodiment of the invention for designing an ophthalmic lens for injection molding a finished progressive lens. The method is directed to use a progressive lens, i.e. a lens with a smooth transition between a far sight portion and near sight portion. Such a lens typically has to have a given diopter, a given progressiveness, a given cylinder value and a given cylinder angle, as for example defined in a prescription issued by a medical doctor or an optician. The method is aimed at making a lens that is to be produced by injecting a polymer mass into a mold on a so-called injection molding machine. Therefore, the method takes into account some of the limitations posed by the manufacturing process. In the exemplary embodiment illustrated in Figs. 1 to 4 the progressiveness of the lens to be manufactured is disposed in the front surface 20 of the lens, whilst the cylinder is disposed in the back surface 23 of the lens. The combined base curve and cylinder strength of the back surface results in a toric or atoric surface. The front surface 20 is preferably aspheric progressive, but could also be progressive whilst the back surface 23 is preferably toric or atoric. One of the main problems associated with this type of lens is the prism effect, called in-out prism for the 0-180° meridian and up- down prism 90-270° meridian. The prism shows itself for instance by large differences in the edge thickness (ET) of the lens at diametrically opposite positions around the periphery of the lens. With the method according to be preferred embodiment the prism effect in combination with edge thickness is optimized.

The exemplary embodiment describes a finished lens with a base power +2, add power +2 (progressiveness), cylinder -2 and cylinder direction angle 0, with a base 6 front curve. The progressiveness of the lens is disposed in the front surface 20 whilst the cylinder value is disposed in the back surface 23 (cylinder plus power result in a torical or atorical back surface).

In a first step the front surface 20 and the back surface 23 are disposed above one another with their optical centers aligned through a shift in the horizontal direction as indicated by the arrow 17 in Fig. IA. This means that the normal 27 to the optical center 26 of the back surface 23 coincides with the optical center 21 of the front surface 20. The progressiveness and asymmetrical near and far vision area location in the front surface 20 causes the optical center 21 of the front surface not to coincide with the geometrical center 22 of the front surface. The optical center of the back surface with the cylinder value typically coincides with its geographical center. The normal 24 to the optical center 21 front surface 20 and the normal 27 to the optical center 26 of the back surface 23 are directed to align with the vertical (vertical as in the drawings, in practice this direction is preferably substantially perpendicular to the rear surfaces of the mold inserts that are used to manufacture the lens).

Thus, after the shift the geometrical center 22 of the front surface 20 is no longer aligned with the geometrical center of the back surface 23. The front surface 20 and the back surface 23 have an equal diameter. After the shift to align the optical centers 21,26 the edges of the front surface not exactly disposed above the edges of the back surface (indicated by the dotted section of the front and back surface in Fig. IA), which results in a loss in effective diameter of the lens resulting from this configuration of the front and back lens surface. Therefore, the front surface 20 and the back surface 23 are theoretically extended (to 83 mm in this example), so that the effective diameter of the lens (75 mm in this example) is not reduced, but at least kept equal to the prescribed diameter. The hypothetical extended surface of the front and back lens surface are shown in Fig. IA as dotted lines, but are not shown in the following drawings. The position of the lens surfaces after the shift to align the optical centers 21,26 is shown in Fig. 1 along the 0-180° meridian. The lens diameter, the central thickness, the edge thickness and other dimensions are indicated in the drawings in millimeters. These values apply only to the exemplary lens described here, and will vary for other values of the base curves, the cylinder value, the cylinder angle and progressiveness, and depending on progressive design. The edge thickness is indicated by "ET", while the central thickness of the lens is indicated by "CT".

In the next step the upper surface 20 is tilted about its optical center 21 to align the edge values to reduce the variation in edge thickness along the periphery of the lens surfaces taking into account the allowed and/or wanted in-out and top down prism.

The optimal tilt angle as for example defined in the 0-180° meridian and as defined in the 90-270° meridian can be determined in accordance with the various known methods. A simple method is based on selecting the tilt angle about the optical center in the plane of the 0-180° meridian to a value that minimizes the in-out prism and reduces the edge thickness variation and selecting the tilt angle about the optical center in the plane of the 90-

270° meridian to a value that minimizes the up-down prism and reduces the edge thickness variation. In the present example, the tilt angle in the 0-180° meridian is selected to be 0.5° whilst the tilt angle in the 90-270° meridian is selected to be 1.2°. It is noted that the process of determining the optical tilt angles can be empiric and does not necessarily result in 0 prism or completely constant edge thickness, but results in a optimum of the combination.

The position of the lens surfaces after these steps is illustrated along the 0- 180° meridian in Fig. 3 and along the 90-270° meridian in Fig. 4.

The tilt has reduced in-out prism to 0.25 diopter in the optical center (Fig. 3) and to 1 diopter up-down prism in the optical center (Fig. 4). Thereafter, the upper lens surface 20 and the lower lens surface 23 are brought closer to one another by moving the lens surfaces towards each other in the direction of optical axis 27 (which is the same as the normal to the optical center 26) of the back surface 23. The upper lens surface 20 and a lower lens surface 23 are moved closer to each other until the minimal edge thickness "ET" reaches a predetermined value, for example about 1 mm. The minimal edge thickness is the distance between the edge of the upper surface 20 and the edge of the lower surface 23 at the position around the periphery of the lens where the edges of the front surface 20 and back surface 23 are closest to one another.

The resulting position is shown in Fig. 5 along the 0-180° meridian and in Fig. 6 along the 90-270° meridian. Please note that Figs. 5 and 6 illustrate the front surface 20 by means of a mold insert 30 with a mold surface 40 and illustrate the back surface 23 by means of a mold insert 33 with a mold surface 43. The mold inserts 30,33 have a disk or cylinder shape with at least one of the surfaces that would be flat in a perfect disk or cylinder being a concave or convex molding surface 40,43. The mold halves (Fig. 13) in which the inserts are received are provided with cylindrical cavities in which the mold inserts 30,33 fit snugly.

The hypothetical optical axis of the mold insert 33 coincides with the axial axis of the mold insert (which in turn coincides with the axial axis of the cavity in the mold halves when the mold insert is placed inside the mold halves).

The contour or shape of mold surface 40 corresponds to the contour or shape of the front surface 20, and for practical reasons there will be referred to an optical center and an optical axis of the mold surface 40, although the mold insert is preferably made of metal and is thus not translucent, so that the mold surface does in reality not have an optical axis and optical center. The same applies to mold surface 42.

The tilt angle is built into the upper mold insert 30, i.e. the normal 24 to the optical center of the mold surface 40 is at an angle with the normal 27 to the optical center of mold surface 43. The tilt angle is shown by the angle between the normal 24 and the vertical since the normal to the optical center 27 coincides with the vertical in the drawings. The orientation of the mold surface 40 without applying tilt is indicated by an interrupted line, for visualizing the tilt of the mold surface 40 about its optical center. The required tilt angle is completely defined by the characteristics of the front surface 20, and not dependent on the characteristics of the back surface 23.

Since this tilt angle is permanently build into the mold insert 30, which defines the mold surface 40 for forming the front surface 20 of the lens 10, it is not necessary to keep the stock of mold inserts 30 with various tilt angles but otherwise identical lens geometries. Thereafter, the mold insert 33 with the mold surface 43 corresponding to the back surface 23 is rotated about its optical axis 27 to obtain the correct cylinder angle. This step is illustrated in Fig. 7. The rotation, which is indicated with vector 27' ensures that the direction of the progressiveness in the front surface 20 is at the correct angle with the cylinder in the back surface 23, as for example specified in the prescription. The resulting position of the front surface 20 and the back surface 23 (shown by the mold inserts 30 and 33 and their respective molding surfaces 40 and 42) with a cylinder angle of 45° is illustrated in Fig. 8 for the 0-180° meridian and in Fig. 9 for the 90- 270° meridian. The resulting position of the front surface 20 and the back surface 23 (shown by the mold inserts 30 and 33 and their respective molding surfaces 40 and 43) with a cylinder angle of 90° is illustrated in Fig. 10 for the 0-180° meridian and in Fig. 11 for the 90-270° meridian. Fig. 12 illustrates a lens 10 designed in accordance with the method according to a preferred embodiment of the invention. The lens 10 has as indicated an optical center 21 of the front surface 20, the normal 24 to the optical center 21 and the original geometrical center 22 of the front surface.

The lens 10 shown in Fig. 12 can be made in one step as a finished lens on an injection molding machine when using the appropriate lens inserts 30, 33. The term finished lens is used to indicate a lens that is complete in shape, except for the cutting of the frame curve of the spectacle in the lens. Further, the "finished" lens 10 is typically coated to make it scratch resistant and/or with an anti reflective coating after it has been molded. The coatings can be applied to the lens in the lens manufacturing facility, typically the scratch resistant coating, but usually the anti-reflective coating is done at finishing-lab where the lenses 10 are also cut to match the shape of the spectacle frame.

Figs. 13-15 illustrate a mold 50 comprising an upper mold half 52 and a lower mold half 54 that are capable of moving towards and away from one another to open and close the mold, for example in order to remove a finished lens. The mold 50 is suitable for use in an injection molding machine (not shown) that is as such well known in the art that includes the systems for moving the mold halves and for delivering polymer mass under pressure to the mold.

A cylindrical jacket 56 determines a cylindrical space in which the mold cavity 70 is disposed. The mold insert 33 with the mold surface 43 for forming the back surface 23 of the lens 10 is received in an upper part 57 of the cylindrical jacket 56 (the terms "upper" and "lower" as used here are with reference to the orientation in the drawings - however, the mold could be placed in other orientations relative to the gravity field). The mold insert 30 with the mold surface 40 for forming the front surface 20 of the lens is received in a lower part 58 of the cylindrical jacket 56. The mold insert 30 is releasably secured in the lower jacket part 58 in a fixed rotational relationship to the lower mold half 54.

The upper mold half is movable in the axial direction relative to the lower mold half between an initial waiting position and a final molding position. The axial movement of mold halves is controlled by hydraulic actuators or by electric actuators (not shown) on of the injection molding machine.

For exchanging mold inserts, the mold half 30 can be drawn into and ejected from the lower mold half by a piston 61 that is connected to the mold insert 30 via a piston rod 60. The axial movement of mold insert 33 in and out of the upper mold half is controlled by a pneumatically operated piston 62 that is connected to the mold insert 33 via a piston rod

59.

The rotational relationship between the mold insert 30 and the lower part 58 of the jacket 56 is preliminary determined by a form fit connection between a recess in the free end of the piston rod 61 and a connection member 81 protruding from the rear surface of the mold insert 30. The exact/final rotational position of the mold insert 30 is determined by a pin 87 that protrudes from the rear surface of the mold insert near the periphery thereof. The pin 87 fits in an exactly positioned hole at the base 91 of the lower part of the jacket 58, and ensures that the mold insert 30 will not be displaced relative to the lower part 58 of the jacket 56 during operation of the injection molding machine.

The rotational relationship between the mold insert 33 and the upper part 57 of the jacket 56 is adjustable. A connection member 80 that protrudes from the center rear surface of mold insert 33 is pivotally suspended from the mold insert 33 about the geometrical axis of the mold insert (the geometrical axis coincides with the optical axis of the back lens surface 23 that corresponds to the mold surface 43). The rotational position of the mold insert 33 is preliminary determined by a form fit connection between the connection member 80 and a recess in the free end of the piston rod 59. The rotational relationship between the connection member 80 and the mold insert 33 is easily adjustable when the mold insert 33 is not inserted in the mold since the connection member 80 is rotably suspended from the mold insert 33. However, in order to avoid inadverted changes in the rotational position of the mold insert 33 relative to the connection member 80 when the mold insert is being inserted into the mold, a friction increasing system 85 is applied to the connection member 80. The friction increasing system 85 includes a radial bore that ends on a tangential surface of the connection member 80. A spring loaded ball that is disposed in the bore applies pressure to a tangential surface of the connection member 80 and thereby ensures that the connection member 80 will not inadvertently be rotated.

The exact/final rotational position of the mold insert 33 is determined by a pin 83 that protrudes from the rear surface 37 of the mold insert 33 near the periphery thereof and is received in one of a plurality of holes arranged as a semicircular array 92 (Fig. 17) in the base 93 of the upper part 57 of the jacket 56. The holes in the array 92 are distributed at 5° or 10° intervals depending on the intervals for the cylinder angle used in the prescriptions and the pin/hole connection ensures that the mold insert 33 is not inadvertently rotated relative to the jacket 56 during operation of the molding machine. Figs. 16-19 illustrate the process of inserting a new mold insert 33 into the mold. For practical reasons only the upper part 57 of the jacket 56 is shown.

Fig. 16 shows a perspective view on the rear of a mold insert 33, with the form fit connection member 82 of the rotatable connection member 80 and the rear surface 37 with the pin 83 clearly visible. The first step for inserting the mold insert 33 into the mold is to set the correct angle for the connection member 80, so that the required cylinder angle for the lens 10 will be obtained. This step is preferably performed on an auxiliary tool (the auxiliary tool will be described in greater detail further below with reference to Fig. 20). There is another auxiliary tool that is provided with a heater to preheat the mold insert before it is placed into the mold, so that the molding process is not delayed by heating the mold insert inside the mold (this auxiliary tool will be described in greater detail further below with reference to Figs. 21 and 22).

It is also possible that only the rotational angle of the mold insert is changed between molding runs, i.e. the same mold insert is used in the next molding run but the rotational position is changed to obtain another cylinder angle.

Fig. 17 illustrates the next step of the process of inserting a new mold insert 33 into the upper half 57 of the jacket. In the upper part of Fig. 17 the mold insert 33 has been attached to the free end 69 of the extended piston rod 59. The lower part of Fig. 17 illustrates the position of the piston rod 59 without the mold insert 33 attached thereto. Fig. 18 illustrates how the piston rod is being retracted by applying air pressure to the pneumatic piston 62, whereby the mold insert 33 is retracted into the upper part 57 of the jacket 56. Fig. 19 illustrates a further stage of retraction of the mold insert 33, of which now only the mold surface 43 is visible, into the upper part 57 of the jacket. The mold insert 33 is retracted into the upper part 57 of the jacket 56 until the rear surface 37 of the mold insert 33 abuts with the base 93 and the pin 83 has engaged one of the holes in the array of holes 92.

The procedure for removing a mold insert 30,33 from the mold is the reverse of the procedure to insert a mold insert into the mold and is caused by the piston 61,62 to expel the mold insert 30,33 by pressure applied via the piston rod 59,60. In order to be able to manufacture individually shaped lenses quickly, a plurality of mold inserts 30 and a plurality of mold inserts 33 are at disposal of the operator of the injection molding machine.

According to a preferred embodiment, the plurality of mold inserts 30 include mold inserts with different progressiveness and different base factors, as well as different tilt angles between the rear surface and the mold surface 40. In order to cover the most common 75% of prescriptions 52 different mold inserts 30 and 175 number of different mold inserts 33 need to be at disposal for the manufacturing process. The plurality of different mold inserts 30 include 2 base curves, and 13 number of levels of progressiveness. The plurality of mold inserts 33 include mold inserts with 25 different base curves and 7 different cylinder values. The correct combination of base powers of the mold insert 30 and the mold insert 33 results in the prescribed diopter value of the lens 10. The correct selection for the mold insert 30 is used to obtain the correct value for the progressiveness and automatically results in the correct tilt angle between the rear surface 37 of the exchangeable mold insert 30 and the mold surface 40 of the exchangeable mold insert 30. The correct selection of the mold inserts 33 is used to obtain the correct cylinder value.

Fig. 20A and 20B show a preferred embodiment of an auxiliary tool 94 according to the invention for adjusting the rotational position of the connection member 80 so that when the connection member 80 enters in a form fit connection with the free end of the piston rod 59, the mold insert 33 is substantially aligned correctly with the jacket 56 of the mold.. The tool 94 includes a disk 95 that is provided with a circular rim 96 and a radially extending slot 97. When the connection member 80 is inserted in the slot 97 there is a form fit connection between the connection member 80 and the disk 95. The rim 96 provides an operator with a grip on the disk 95, and assisted by a scale that is printed on the periphery of the disk 95 the operator can turn the disk and therewith the connection member 80 the desired angular position.

Figures 21 and 22 illustrate a preferred embodiment of an auxiliary tool 110 according to the invention for preheating mold inserts 30,33. The auxiliary tool 110 comprises a plate-like body provided with four cylindrical recesses 112, in which mold inserts 30,33 can be received for heating them up before placing them in the mold of a molding machine. It is noted that the auxiliary tool 110 could be provided with fewer or with more than four recesses 112, in accordance with needs. The auxiliary tool 110 includes heating elements 114 that could be either conduits through which hot water or oil is passed or electrically operated heating elements (not shown). The auxiliary tool 110 comprises an upper insulation plate 118 and a bottom insulation plate 116. Two steel plates 120 are sandwiched between the upper insulation plate 118 and the bottom insulation plate 116.

Several auxiliary tools 110 may be provided for one mold 50, so that a plurality of mold inserts 30 or 33 can be preheated in time before they are inserted into the mold 50.

After closing the mold, the injection molding machine injects an amount of a hot polymer mass, such as polycarbonate, into the mold cavity 70 that is defined inside the cylinder formed by the jacket 56 between mold surface 40 and mold surface 43. When the mold cavity 70 has been filled with pressurized polymer mass, the mold 50 is kept in the closed position for a period of time and during this period water cooling of the mold inserts and eventually the jacket is applied until the material in the mold cavity 70 is sufficiently rigid for the now produced lens 10 to be ejected from the mold. Then, the injection molding machine moves the mold halves away from one anther to open the mold, so that the manufactured lens 10 can be removed. When a run of one or more lenses has been manufactured, the mold inserts 30 and 33 are replaced by others in order to start a molding run with a different lens geometry. The appropriate mold insert 30 and mold inserts 33 for the next individually shaped progressive lens 10 to be produced have already been selected from the plurality of mold inserts that are at the disposal of the operator of the injection molding machine. The selected mold inserts 30 and 33 for the next run have already been heated up in the auxiliary device 110 and the angle for the connection member 80 has already been adjusted in the auxiliary device 94 to match the prescribed cylinder angle. The preheated mold insert 30 and the preheated and adjustable mold insert 33 are then inserted into mold 50 as described above and then the mold 50 is ready to produce a next run of an individually shaped progressive lens. The method of addapting individually shaped progressive lens designs and the method of injection molding individually shaped progressive lenses enables progressive lenses to be manufactured for substantially less costs than with conventional manufacturing techniques that are based on producing a great variety of blanks followed by finishing the blanks individually to meet the prescription, e.g. by polishing at a laboratory or at an optician.

The invention has been described with reference to the embodiments above that apply the progressive surface to the front of the lens and the cylindrical surface to the back of the lens. However, the invention could also be used with lenses in which the progressiveness is in the back surface and the cylinder is in the front surface. Further, the front surface could be progressive or aspheric progressive. The back surface can be toric, or aspheric toric (atoric). These various front and back services can be freely used in any combination.

The invention has been described with reference to a lens with specific diopter values, effective diameter and specific values of edge and central thickness. It is, however, understood that the presented values are only exemplary, and that the invention can equally be implemented for lenses with other diopter values, progressiveness levels, cylinder values and diameters.

The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality.

The reference signs used in the claims shall not be construed as limiting the scope.

Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.

Claims

CLAIMS:

1. An ophthalmic lens with a front and a back surface, one of which is progressive and the other is torical or atorical, which surfaces having a geometry that matches a given diopter value, a given cylinder value and a given cylinder angle, whereby the optical center of the front surface is aligned with the optical center of the back surface.

2. A method for designing an ophthalmic lens with a front and a back surface, one of which is progressive and the other is torical or atorical, said lens requiring a given diopter value, a given cylinder value and a given cylinder angle, said method comprising:

- determining a combination of a progressive surface geometry and an atoric or toric surface geometry that matches the given diopter value and given cylinder value,

- aligning the optical center of the front surface with the optical center of the back surface by shifting the front surface relative to the back surface until the optical axis of the front surface substantially coincides with the optical center of the back surface or until the optical axis of the back surface coincides with the optical center of the front surface.

3. A method according to claim 2, further comprising tilting the back surface and/or the front surface about their/its optical center to optimize the balance between reduction of distance variation between the edges of the front surface and the back surface and wanted or allowed prism effect of a resulting lens.

4. A method according to claim 2 or 3, further comprising adjusting the distance between the front surface and the back surface to obtain a given value for the minimum distance between the edges of the front surface and the back surface.

5. A method according to claim 2 or 4, wherein the finished lens has to have a given diameter before it is cut to match the contour of the spectacle frame in which it is to be used, and comprising the step of selecting the diameter of the front surface and of the back surface to compensate for reduction in lens diameter caused by said shift of the front surface relative to the back surface.

6. A method according to any of claims 2 or 5, further comprising rotating the back surface about its optical axis to obtain said given cylinder angle.

7. A method according to any of claims claim 2 to 6, wherein the front surface is either progressive or aspherical progressive.

8. A method according to any of claims 2 to 7, wherein the front or back surface is tilted about its optical center, whilst the opposite surface is not tilted about its optical center.

9. A method according to any of claims 2 to 8, further comprising manufacturing exchangeable mold inserts with surfaces corresponding to the designed lenses.

10. An ophthalmic lens designed with the method according to any of claims 2 to

9.

11. A method for manufacturing a finished progressive ophthalmic lens with a given diopter value, a given cylinder value and a given cylinder angle on an injection molding machine with at least two mold halves, comprising:

- providing a first mold insert with a surface with a contour corresponding to the front surface of the lens to be manufactured,

- providing a second mold insert with a surface with a contour corresponding to the back surface of the lens to be manufactured, - placing said first mold insert in one of the mold halves,

- placing said second mold insert in the other mold half with the position on the surface of the second mold insert that corresponds to the optical center of the back surface of the lens and the position on the surface of the first mold insert that corresponds to the optical center of the front surface of the lens substantially coinciding with the normal to the optical center of the front surface or with the normal to the optical center of the back surface.

12. A method according to claim 11, further comprising rotating one of the mold inserts about an axis that substantially coincides with the normal to the optical center of the lens surface that it corresponds to for obtaining the required cylinder angle for the lens.

13. A method according to claim 10, 11 or 12, further comprising providing a plurality of first mold inserts with various geometries, providing a plurality of second mould inserts with various geometries, and selecting a combination of a first mold insert and a second mold insert that results in the required diopter value, cylinder value and progressiveness.

14. A method according to claim 13, further comprising disposing the progressive surface of the lens on either the front surface or back surface of the lens, and shifting the optical center of the mold insert surface that corresponds to the progressive lens surface to coincide with the geometrical center of the mold insert concerned.

15. A method according to any of claims 10 to 14, further comprising the step of providing first mold inserts with a mold surface corresponding to a progressive front surface of the lens to be produced in which the direction of the normal to the optical center to the front surface relative to the axial axis of the mold insert is adapted in order to optimize the balance between reduction of the variation in edge thickness of the lens to be produced and alowed and /or wanted prism in the lens to be produced.

16. A method according to claim 15, wherein the cylinder is formed in the back surface.

17. A set of exchangeable mold inserts for use in an injection molding machine to manufacture progressive ophthalmic lenses, said set comprising: - a plurality of first mold inserts with a mold surface corresponding to the front surface of a lens to be produced,

- a plurality of second mold inserts with a mold surface corresponding to the back surface of a lens to be produced,

- the first and/or second mold inserts being provided with a surface that corresponds to a progressive lens surface in which the geometrical center does not coincide with the optical centre, and wherein the mold surfaces on the first mold inserts and the mold surfaces on the second mold insert are disposed such that the normal to optical center of the lens surface corresponding to the mold surface of the first mold insert substantially coincides with the optical center of the lens surface corresponding to the mold surface of the second mold insert or are disposed such that the normal to optical center of the lens surface corresponding to the mold surface of the second mold insert substantially coincides with the optical center of the lens surface corresponding to the mold surface of the first mold insert when a pair of a first mold insert and a second mold insert is inserted in the molding machine.

18. A set of exchangeable mold inserts for use in an injection molding machine to manufacture progressive ophthalmic lenses, said set comprising:

- at least one first mold insert with a mold surface corresponding to a progressive front or back surface of a lens to be produced, - at least one second mold insert with a mold surface corresponding to the front or back surface opposite to the progressive surface of a lens to be produced, wherein the mold surface of the first mold insert is tilted about the optical center of the lens surface to which the mold surface corresponds, so that the normal to the lens surface to which the mold surface of the first mold insert corresponds is at an angle with the normal to the lens surface to which the mold surface of the second mold insert corresponds in order to optimize the balance between the reduction of the variation in edge thickness and prism effect of the lens to be produced.

19. A set of exchangeable mold inserts according to claim 18, wherein said mold inserts have substantially cylindrical bodies and wherein the normal to the optical center of the lens surface to which the mold surface of the second mold insert corresponds substantially coincides with axial axis of the body of the second mold insert, and the normal to the optical center of the lens surface to which the mold surface of the first mold insert corresponds is not parallel with the axial axis of the body of the first mold insert.

20. A set of exchangeable mold inserts according to claim 19, wherein the optical centre of the surface to which the first mold insert corresponds coincides with the axial axis of the body of the first mold insert.

21. A mold insert for use in an injection molding machine to manufacture progressive ophthalmic lenses, said mold insert being provided with a mold surface corresponding to the front surface or to the back surface of the lens to be manufactured, said mold insert being provided with means for selectively presetting the angular position of the mold insert concerned as measured about the optical axis of the lens surface corresponding to the mold surface of the insert relative to the molding machine in which said mold insert is to be placed.

22. A mold insert according to claim 21, wherein said means for selectively setting the angular position of the mold insert comprise a connection member that is pivotally suspended from the mold insert about an axis that substantially coincides with the optical axis of the lens surface to which the mold surface corresponds.

23. A mold insert according to claim 22, further comprising means to controllably cause friction between the mold engaging member and the mold insert to avoid inadverted rotational movement of the mold engaging member relative to the mold insert.

24. A mold insert according to claim 22 or 23, wherein said connection member shaped for engaging a piston rod of said molding machine in a form fit connection.

25. A mold insert according to claim 24, wherein said connection member protrudes from a rear surface of said mold insert that is disposed opposite to said molding surface.

26. A method for manufacturing ophthalmic lenses on an injection molding machine between a first exchangeable insert with a mold surface with a contour corresponding to the front surface of the lens to be manufactured and a second exchangeable insert with a mold surface with a contour corresponding to the back surface of the lens to be manufactured, comprising: - providing a plurality of first mold inserts with a variety of different surface contours,

- providing a plurality of second mold inserts with a variety of different surface contours,

- preheating a first and/or second mold insert that have surfaces that correspond to a lens to be manufactured during one of the next mounding cycles,

- exchanging the first and/or second mold inserts in the molding machine with preheated first and/or second mold inserts, and

- molding said individually contoured lens to be manufactured.

27. A method according to claim 26, further comprising providing an auxiliary tool for preheating said mold inserts.

28. A method according to claim 11, 26 or 27, further providing an auxiliary tool for setting the rotational position of a mold insert relative to the mould halves, said rotational position being measured around the optical axis of the lens surface that corresponds to the surface of the mold insert.

29. A method according to claim 11, 26 or 27, further comprising the step of adjusting the angular position of the mold insert relative to the mold when said mold insert is already present in the mold.

30. A method according to claim 26, 27 or 28, in which the step of exchanging the first and/or second mold inserts in a molding machine comprises the step of inserting the first or second mold insert into a half of a jacket, comprising:

- connecting the mold insert to a free end of an extended piston rod of a piston, and - retracting the piston rod whereby the mold insert is retracted into a jacket.

31. A method according to claim 30, in which the step of inserting the first or second mold insert into a half of a jacket further comprises the step of further retracting the piston rod until a rear surface of the mold insert abuts with a base of the jacket and a pin that protrudes from the rear surface of the mold insert near the periphery thereof engages one of a plurality of holes arranged as a semicircular array in the base of the jacket.

32. An auxiliary tool for adjusting the preset angular position of the mold insert according to any of claims 26 to 31 relative to the mold of the molding machine in which said mold insert is to be placed.

33. An auxiliary tool according to claim 32, comprising means for engaging the connection member of the molt insert and means for indicating the angular position of said connection member relative to the molt insert.

34. An auxiliary tool for preheating mold inserts that are provided with a molding surface that corresponds to the front surface or to the back surface of an ophthalmic lens.

35. An auxiliary tool according to claim 34, comprising a housing with one or more cylindrical recesses for receiving said mold inserts therein.