TECHNICAL FIELD

The present disclosure relates to a finished uncut spectacle lens, to a semi-finished lens blank used for manufacturing a spectacle lens and to a method of manufacturing a spectacle lens. In particular, the disclosure relates to a spectacle lens having improved design for manufacturing without affecting the optical properties for the wearer, as well as to a semi-finished lens blank used for manufacturing such a spectacle lens as well as to the manufacturing of such a spectacle lens. Specifically the disclosure facilitates making spectacle lenses as thin as possible in the section that is glazed to the frame, while enabling the spectacle lens outside of the frame to be made thicker and to a uniform diameter for the benefit of the manufacturing steps prior to glazing, without increasing the complexity of the lens back surface.

BACKGROUND

These days, the manufacturing of a surfaced spectacle lens is largely automated. The manufacturing starts with calculating the individualized lens based on prescription data received from an eye care professional. The calculated data is then made available to the machines used in the manufacturing process. Based on the data calculated from the prescription, a semi-finished lens blank is selected from which the spectacle lens will be manufactured. These semi-finished lens blanks are sometimes called “pucks” because of their shape. They typically have a front surface already in the correct spherical form, usually needing only the back side to be cut and polished to produce a back surface reflecting the individual prescription for the wearer. After selecting the semi-finished lens blank, its front surface is attached to a standardized block by which it can be held while the back surface is cut and polished to a shape calculated from the data contained in the prescription. After the cutting and polishing processes, the lens back surface combined with the front surface provides a lens having the optical correction specified in the prescription when mounted in the frame.

During the machining step the diameter of the semi-finished lens blank is normally reduced to a value smaller than the original semi-finished lens blank, but larger than the dimensions of the frame to which it is to be fitted. This process is commonly termed cribbing. The spectacle lens which has its final shape for front and back surface but is cribbed to a size larger than the frame is commonly referred to as a finished uncut spectacle lens. The reduced diameter of the finished uncut spectacle lens may be circular or elliptical, or may be complex in shape. Spherical prescriptions in the plus range typically have a physical form being thicker in their geometric center and thinner at the edge; these prescriptions are more likely to benefit from a complex cribbing shape to remove any thin edges of the finished uncut spectacle lenses when they occur around the perimeter, while still keeping the cribbing shape larger than the frame area. These thin edges are otherwise liable to break in the machining process, or cause cuts for instance during manual handling, or to the soft polishing pads.

Optional steps like tinting may be applied to the finished uncut spectacle lens, and it may be coated for instance to make its surfaces scratch resistant and durable. Further treatments, such as for example anti-reflective, anti-fog, and easy-clean coatings, may also be applied.

The glazing process comprises a careful diameter reduction of the finished uncut spectacle lens, usually to micrometer precision, to adapt it to the frame. At this time the edge may be specially shaped, for instance having a bevel applied, to enable it to key into the frame for a secure fit.

It is beneficial to have the cribbed shape of the finished uncut spectacle lens larger than the frame shape until the final glazing step so that any coating defects around the edge such as coating clip marks, resin roll backs, etc., are removed by the edging process for glazing the spectacle lens to the frame. Further, it would be advantageous for the cribbed diameter to be circular, and also to be the same for all spectacle lenses, for various manufacturing steps such as enabling a single size of the supportive blocking mount, to simplify the polishing method, and to facilitate robotic handling of the finished uncut spectacle lenses during which the finished uncut spectacle lenses are held by their cribbed edge. If a single circular diameter was chosen, it would need to be large enough to encompass the largest frame size for spectacle lenses being ordered. Also the cribbed edge would need to have a minimum thickness to provide physical stability during these steps, avoiding edge chips and preventing cuts due to sharp edges during manual handling and cuts to polishing pads.

Unfortunately, having a large circular cribbed shape is problematic for the production of spectacle lenses having positive spherical prescriptions. These spectacle lenses typically have a convex front surface and a concave back surface where the curvature of the back surface is flatter than the curvature of the front surface. As a consequence of this physical form, the thickness at the geometric center of the spectacle lens is limited by the edge thickness of the spectacle lens; if a fixed target edge thickness is maintained, then the center thickness of the spectacle lens will increase with increased spectacle lens diameter. For example, two finished uncut spectacle lenses made with the same 8D front curvature, the same refractive index of 1.5 and the same +5D sphere prescription and 1 mm edge thickness would have different thickness in the geometrical center if one of it had a cribbed diameter of 50 mm while the other one had a cribbed diameter of 70 mm. The 50 mm diameter finished uncut spectacle lens would have a thickness in the geometrical center of 4.2 mm compared to 7.5 mm for the 70 mm diameter finished uncut spectacle lens. After glazing to the frame, the spectacle lens that had been originally cribbed to the larger diameter would be thicker and heavier, and would be least preferred by the wearer.

To enable spectacle lenses to be made as thin as possible, the diameter of the finished uncut spectacle lenses is normally kept as small as possible while still enabling a limited extent of surface extending beyond the contour of the frame to which the spectacle lens shall be glazed. As an alternative, the back surface of the semi-finished lens blank may be machined such that the back surface of the finished uncut spectacle lens is made deliberately steeper in the peripheral zone to thicken the finished uncut spectacle lens outside of the frame shape. The use of this style of lenticular back surface can enable a suitable cribbed edge thickness with a large circular crib shape without significant increase to the thickness of the spectacle lens region that is glazed to the frame. This method has been described in US 2012/0013846 A1 and WO/2019/106399. A drawback of this way of increasing the edge thickness of the finished uncut spectacle lens is the much increased complexity of the back surface shape which requires a slower cutting process in order to maintain the surface design integrity, and which is also difficult to uniformly polish.

SUMMARY

It is an first of the present disclosure to provide a method of manufacture that allows for producing a finished uncut spectacle lens without slowing down the machining step for machining the back surface of the spectacle lens. It is a further objective of the present disclosure to provide a finished uncut spectacle lens with a sufficient diameter of the cribbed edge which can be manufactured without slowing down the machining step for machining the back surface of the semi-finished lens blank used in the manufacturing process considerably and, in many cases, with the same simple uniformity of back surface design as the smaller finished uncut spectacle lens. It is another objective of the present disclosure to provide a semi-finished lens blank that allows for producing a finished uncut spectacle lens without slowing down the machining step for machining the back surface of the spectacle lens and it is a fourth objective. Further, it is an additional objective of the present disclosure to enable a much reduced requirement for the back surface lenticular modification in the case that it should still be required for the particular spectacle lens prescription, frame size, lens material, crib diameter, and edge thickness.

The first objective and the additional objective are achieved by a method of manufacture a finished uncut spectacle lens, wherein the semi-finished lens blank has a peripheral lentic zone in which the curvature of the curved front surface deviates from the convex curvature of the optical bowl. The second objective and the additional objective are achieved by a finished uncut spectacle lens having a concavely curved back surface which includes a concave effective curvature which provides, together with the convex curvature of the optical bowl, a prescribed optical correction. The third objective and the additional objective are achieved by a semi-finished lens blank, wherein the radius of curvature of the front surface in the peripheral lentic zone is an infinite radius.

According to a first aspect, the disclosure provides a method of manufacturing a finished uncut spectacle lens that includes:

obtaining prescription data representing a prescribed optical correction for a wearer of the finished uncut spectacle lens to be manufactured;

providing a semi-finished lens blank with a curved front surface including an optical bowl with a convex curvature; and

machining the semi-finished lens blank to create the finished uncut spectacle lens based on the prescription data.

In the disclosed method, a semi-finished lens blank is used that has a peripheral zone in which the curvature of the curved front surface deviates from the convex curvature of the optical bowl, in other words, the disclosed method uses an inventive semi-finished lens blank. A deviation of the curvature of the curved front surface from the convex curvature of the optical bowl means that the curvature in the peripheral zone is described by different parameter values than the convex curvature of the optical bowl. For example, the convex curvature of the optical bowl may be described by a certain value of a radius of curvature or by certain values of two radii of curvature if the optical bowl has a toric curvature where the value of a radius of curvature or the values of radii of curvature of the front surface in the peripheral zone differs/differ from the respective value/values of the curvature/curvatures of the optical bowl.

The use of an inventive semi-finished lens blank in the disclosed method allows a sufficient edge thickness of the finished uncut spectacle lens which facilitates manufacturing of the spectacle lens, as has already been described with respect to the inventive finished uncut spectacle lens and with respect to the inventive semi-finished lens blank. For further details it is referred to the corresponding explanations made with respect to the inventive spectacle lens and with respect to the inventive semi-finished lens blank.

In the disclosed method, the step of providing a semi-finished lens blank typically includes a step of selecting a semi-finished lens blank in which the convex curvature of the optical bowl already matches the curvature of the front surface of the spectacle lens to be manufactured, i.e., selecting an semi-finished lens blank having a convex curvature of the optical bowl that is suitable for the spectacle lens prescription, and the machining of the semi-finished lens blank is done solely by machining its back surface. Additionally or alternatively, the step of providing the semi-finished lens blank may include a step of selecting a semi-finished lens blank the optical bowl of which has dimensions large enough to cover the whole frame contour of a frame according to obtained frame data. To this end, the frame data may be included in the prescription data. Typically, a semi-finished lens blank is selected, the optical bowl of which has dimensions such that the diameter of the optical bowl is just larger than the frame contour.

Alternatively, the step of providing a semi-finished lens blank may include a step of obtaining frame data and a step of surfacing the optical bowl of an existing standard semi-finished lens blank, i.e., a semi-finished lens blank with a standard convex curvature and a standard diameter of the optical bowl, based on the prescription data and the frame data to form a customized convex curvature and customized dimensions of the optical bowl. Such surfacing can be done using standard digital surfacing processes applied to the front surface of the semi-finished lens blank. This would enable a bespoke choice of optical bowl dimensions for the particular prescription and frame data, with the aim to match the optical bowl size more closely to the frame dimensions of the individual spectacle lens request, enabling the finished spectacle lens center thickness to be minimized for the desired diameter of the finished uncut spectacle lens and the cribbed edge thickness.

The disclosed method may include a step of obtaining frame data and a step of calculating a surface representation of the back surface to be achieved by the machining step, wherein in the calculation of the surface representation accounts for the dimensions of the optical bowl and the frame data such that the center of the surface representation is offset from the center of the finished uncut spectacle lens. The machining of the back surface of the semi-finished lens blank is done such as to achieve the back surface according to the calculated surface representation. When calculating the surface representation of the back surface to be machined, the center would be positioned relative to the geometric center of the finished uncut spectacle lens such that the frame contour of the glazed spectacle lens is positioned centrally within the optical bowl diameter with sufficient clearance so that the glazed spectacle lens includes only the optical bowl on its front surface and none of the peripheral lentic zone.

The calculation would ensure a minimum thickness within the perimeter of the frame contour, in order to satisfy impact strength requirements of the spectacle lens. Additionally, it would ensure a minimum thickness over the body of the finished uncut spectacle lens, which depending on the spectacle lens material might for instance be a minimum of 0.3 mm. Typically, this minimum thickness might occur at the position of the optical bowl diameter. The calculation would also ensure a minimum cribbed edge thickness which might be the same or greater than the criteria for minimum thickness in the body of the finished uncut spectacle lens.

The machining process steps would include selecting an appropriate diameter of blocking medium for mounting the semi-finished lens blank on a machining block and providing both the surface shape and height of the back surface to achieve a finished uncut spectacle lens having the desired optical power and thickness at the geometric center. The machining height calculations are made more complex by the unique front surface shape of the inventive semi-finished lens blank depending upon the diameter at which the front surface is supported by the blocking medium, the position of the front surface of the blocked lens might depend only on the sag of the optical bowl, or also include the sag of the peripheral lentic zone.

The calculation of the representation of the back surface could also include determining a lenticular back surface in the peripheral lentic zone to be used in conjunction with the inventive semi-finished lens blank if required to better minimize the center thickness of the finished uncut spectacle lens while maintaining the desired crib diameter and minimum thickness requirements at the position of the cribbed edge and the diameter of the optical bowl, in the manner previously described in WO/2019/106399. To this end, the method includes a step obtaining frame data and a step of calculating a modified back surface to be formed by the machining step, wherein a lenticular back surface is calculated based on the dimensions of the optical bowl, the frame data, the prescription data, and minimum lens thickness requirements. As previously noted, this lenticular back surface could be made simpler as compared to the related art where the minimum cribbed edge thickness must be achieved solely by a deviation of the curvature of the back surface in the peripheral lentic zone, without any thickness contribution from the front surface in a peripheral lentic zone.

According to a second aspect, the disclosure provides a finished uncut spectacle lens that comprises a curved front surface including an optical bowl with a convex curvature. Typically, the lateral dimensions of the optical bowl are large enough to fully receive a frame contour of a frame to which the spectacle lens is to be glazed. In addition, the finished uncut spectacle lens comprises a peripheral lentic zone surrounding the optical bowl. In the inventive finished uncut spectacle lens the curvature of the curved front surface in the peripheral lentic zone deviates from the convex curvature of the optical bowl. A deviation of the curvature of the curved front surface from the convex curvature of the optical bowl means that the curvature in the peripheral lentic zone is described by different parameter values than the convex curvature of the optical bowl. For example, the convex curvature of the optical bowl may be described by a certain value of a radius of curvature or by certain values of two radii of curvature (in case of a toric front surface) where the value of a radius of curvature or the values of radii of curvature of the front surface in the peripheral lentic zone differs/differ from the respective value/values of the radius/radii of curvature/curvatures of the optical bowl. In common ophthalmic nomenclature the peripheral lentic zone would be termed a front surface lentic.

With the inventive finished uncut spectacle lens, a large uniform circular crib shape can be enabled that is usable for all spectacle lens prescriptions—or at least for a large number of spectacle lens prescriptions. In addition, the inventive finished uncut spectacle lens ensures that the edge thickness at the cribbed edge does not fall under a minimum edge thickness for all spectacle lens prescriptions, or at least for a large number of spectacle lens prescriptions, without needing to thicken the geometric center of the finished uncut spectacle lens, even for spectacle lenses having a positive spherical prescription. The uniformity of crib diameter and ensuring not to fall below a minimum edge thickness for all spectacle lens prescriptions facilitates processing and handling of the finished uncut spectacle lens, in particular robotic handling. In addition, the shape of the back surface of the finished uncut spectacle lens does in most cases not need to be altered in order to increase its edge thickness, meaning the back surface is simplified for the machining and polishing processes. For instance, in the case of a prescription requiring a spherical or toroidal back surface, the finished uncut spectacle lens could be polished using even a conventional hard-lap method.

To satisfy impact strength requirements the finished uncut spectacle lens should have sufficient thickness over the contour of the frame. Additionally, in order for the finished uncut spectacle lens to be physically robust in the manufacturing process, including both robotic and manual handling, it requires a minimum thickness over the full diameter of the finished uncut spectacle lens. Due to the front surface geometry, and depending on the back surface shape and any prism of the spectacle lens, the minimum lens thickness of the inventive finished uncut spectacle lens will likely be positioned at the intersection of the optical bowl and the peripheral lentic zone. Depending on the lens material, a typical minimum thickness over the body of the finished uncut spectacle lens may, for example, be 0.3 mm. The minimum cribbed edge thickness may be specified separately, and for instance may be the same criteria as the minimum thickness in the body of the finished uncut spectacle lens, or a larger minimum, for instance 0.5 mm.

Typically, the convex curvature of the optical bowl is steeper than the curvature of the front surface in the peripheral lentic zone. In other words, the typically spherical convex curvature of the optical bowl has a first radius of curvature, and the curvature of the front surface in the peripheral lentic zone has a second radius of curvature. The second radius of curvature is larger than the first radius of curvature. This makes the convex curvature of the optical bowl steeper than the curvature of the front surface in the peripheral lentic zone, which increases the distance between the front surface of the finished uncut spectacle lens and the back surface of the finished uncut spectacle lens at its cribbed edge, thus increasing the thickness of the finished uncut spectacle lens at its cribbed edge. In case the convex curvature of the optical bowl is toric, the convex curvature would have a first radius of curvature in a first meridian and a second radius of curvature in a second meridian. Then, the curvature of the front surface in the peripheral lentic zone would have radii of curvature in these meridians which are larger than the respective radii of curvature of the optical bowl.

The inventive finished uncut spectacle lens has a curved back surface that includes a concave effective curvature which provides, together with the convex curvature of the optical bowl, a prescribed optical correction. The radius of curvature of the effective curvature is smaller than the radius of curvature of the front surface in the peripheral lentic zone. In particular, the radius of curvature of the front surface in the peripheral lentic zone may be an infinite radius or flat, which means that the curvature of the back surface is always steeper than the curvature of the front surface in the peripheral lentic zone.

In some cases, it might be advantageous that the curvature of the back surface also deviates in the peripheral lentic zone from that needed for the optical prescription, in order to further thicken the edges of the finished uncut spectacle lens outside of the frame contour. By this measure, the thickness of the finished uncut spectacle lens in its geometrical center can be further reduced. However, it should be noted that such a deviation of the curvature of the back surface in the peripheral lentic zone could be made simpler as compared to the related art where the increased edge thickness must be achieved solely by a deviation of the curvature of the back surface in the peripheral zone, without any thickness contribution from the front surface shape of a peripheral lentic zone.

In the inventive finished uncut spectacle lens, the optical bowl with the convex curvature and/or the effective curvature of the back surface may extend over an area of the finished uncut spectacle lens that is large enough to cover a frame contour of a frame to which the spectacle lens shall be glazed; while it could in principle be smaller, it is desirable to avoid optical aberrations in the peripheral view of the wearer as well as in view of the aesthetic perception of the glazed spectacle lenses.

The present disclosure is particularly useful for spectacle lenses with a positive spherical power which typically have a back surface that is flatter than the front surface. Although spectacle lenses with positive spherical power having a convex front surface as well as a convex back surface are possible, such spectacle lenses are not common due to aesthetic reasons. However, also in such cases the present disclosure can be used.

According to a third aspect of the present disclosure, a semi-finished lens blank for use in manufacturing a spectacle lens is provided. The semi-finished lens blank has a curved front surface including an optical bowl with a convex curvature and a peripheral lentic zone surrounding the optical bowl. The curvature of the curved front surface in the peripheral lentic zone deviates from the convex curvature of the optical bowl.

The inventive semi-finished lens blank, the front surface of which typically already corresponds to the front surface of the spectacle lens to be manufactured, can be used in manufacturing the inventive finished uncut spectacle lens, delivering all of the advantages that have been described. Thus, when a finished uncut spectacle lens is made from the inventive semi-finished lens blank to a particular thickness at geometric center, the front surface at the outer diameter which includes the peripheral lentic zone is positioned further from the back surface than in the case of a finished uncut spectacle lens made with a uniformly spherical front surface; accordingly the finished uncut spectacle lens will have a larger edge thickness when using the inventive semi-finished lens blank compared to a related art spherical semi-finished lens blank. In case of spectacle lenses with a prescription including a positive spherical power, the physical form of the spectacle lens is such that the center thickness of the spectacle lens is limited by the edge thickness; the use of the inventive semi-finished lens blank enables a smaller center thickness at a given finished uncut spectacle lens diameter, compared to a related art semi-finished lens blank.

The front surface of the inventive semi-finished lens blank could be made by a casting process in mass-manufacturing, in which case the front surface would be created by the front mold used to cast the blank. In the same way that semi-finished lens blanks are made in a range of base curves, a series of inventive semi-finished lens blanks could be produced having a range of optical bowl curvatures to accommodate different prescriptions of the finished spectacle lens. Additionally, these inventive semi-finished lens blanks could be made with a range of curvatures in the peripheral lentic zone. Further, they could be made with a range of optical bowl sizes, to accommodate different frame sizes.

Alternatively, the inventive semi-finished blanks could be made using digital surfacing and polishing processes applied to the convex surface of a related art semi-finished lens blank. This approach would enable a bespoke choice of optical bowl curvature, peripheral lentic zone curvature and optical bowl diameter, optimized to the prescription and frame of the spectacle lens request. Since the peripheral lentic zone of the inventive finished uncut spectacle lens would not appear within the glazed spectacle lens, it would not need to be manufactured to the same standard as the optical bowl for surface power or cosmetic quality, needing only to deliver the correct physical form to modify the front surface sag and deliver the expected edge thickness increase in the finished uncut spectacle lens.

Typically, the convex curvature of the optical bowl is steeper than the curvature of the front surface in the peripheral lentic zone. In other words, the typically spherical convex curvature of the optical bowl has a first radius of curvature, and the curvature of the front surface in the peripheral lentic zone has a second radius of curvature. The second radius of curvature is larger than the first radius of curvature. This makes the convex curvature of the optical bowl steeper than the curvature of the front surface in the peripheral lentic zone, which increases the distance between the front surface of the finished uncut spectacle lens and the back surface of the finished uncut spectacle lens at its cribbed edge, thus increasing the thickness of the finished uncut spectacle lens at its cribbed edge. In case the convex curvature of the optical bowl is toric, the convex curvature would have a first radius of curvature in a first meridian and a second radius of curvature in a second meridian. Then, the curvature of the front surface in the peripheral lentic zone would have radii of curvature in these meridians which are larger than the respective radii of curvature of the optical bowl. As already mentioned with respect to the inventive finished uncut spectacle lens this helps to prevent the front surface from eventually intersecting the back surface.

In order to allow to manufacture finished uncut spectacle lenses in which the optical bowl with the convex curvature extends over an area of the spectacle lens that is large enough to cover a frame contour of a frame to which the finished uncut spectacle lens shall be glazed, the semi-finished lens blank includes an optical bowl with a convex curvature which extends over an area of the semi-finished lens blank that is large enough to cover the frame contour of the respective frame.

In the inventive semi-finished lens blank, the radius curvature of the front surface in the peripheral lentic zone may be an infinite radius. This is advantageous for the same reasons that have already been described with respect to the inventive spectacle lens. It is therefore referred to the explanations made with respect to the inventive spectacle lens.

In addition, the disclosure provides a method of manufacturing a finished uncut spectacle lens. The method includes:

obtaining prescription data representing a prescribed optical correction for a wearer of the finished uncut spectacle lens to be manufactured;

providing a semi-finished lens blank with a curved front surface including an optical bowl with a convex curvature; and

machining the semi-finished lens blank to create the finished uncut spectacle lens based on the prescription data.

