Patent Description:
The capability of the eye to focus on objects at different distances may be limited of different reasons. Typically, this capability is reduced as a function of age. Then it may be necessary to use different spectacles having different optical powers, or spectacles with different or variable optical powers like bifocal or progressive spectacles.

Although these solutions are of great benefit, the need for switching between different spectacles or using spectacles with different built-in optical powers are not optimal as compared with the sight of a person with non-degraded focusing capabilities.

<CIT> discloses a tunable lens with two transparent cover members, a piezoelectric actuator system, a rigid frame and a non-fluid body which may be used in spectacles.

<CIT> a liquid filled adjustable spectacles lens with deformable non-round membrane assembly in which the shape of a membrane is controllably adjustable by altering the fluid pressure across the membrane.

<CIT> discloses a mechanically tunable spectacle lens.

In <CIT>, bending piezo-electric elements are arranged in a pattern on the transparent cover which shape the tunable lens body.

<CIT> discloses a tunable lens in which the actuator is applying a force upon the flexible layer for bending the layer.

<CIT> discloses variable power spectacles with two linked adjustment mechanisms.

Accordingly, it is an object to improve spectacles with respect to the above mentioned problems and other limitations of presently available spectacles.

It is an object of the invention to improve spectacles, particularly to provide spectacles which provides different optical powers in a more user-friendly way than traditional spectacles. It is also an object of the invention to further improve the sight of a person with degraded focusing capabilities or which suffers from other sight limitations as compared with presently available spectacles.

In a first aspect of the invention there is provided a spectacle lens which comprises.

Advantageously, the controllable actuators enables control of the optical power of the lenses in a pair of spectacles implying that the optical power of the lenses can be changed without the user needs to gaze through different portions of the lenses to access different optical powers as in traditional multi-focal or progressive lenses.

Advantageously the transparent, deformable, non-fluid body supports the bending of the first or second cover member so that the resulting curvature of the bending approximates a spherical shape. That is, polymers which are used for the non-fluid body creates a non-uniform distribution of the force applied to the cover members when actuators are activated. In comparison, the hydrostatic pressure in liquid is the same everywhere in liquid. A non-uniform force distribution can be advantageous in some situations to create a spherical deformation profile. Further, the non-fluid body is not significantly sensitive to gravity as compared with liquid. Thus, optical errors due to gravity effects is limited due to use of the non-fluid body.

According to the invention, the one or more actuators are arranged to generate the forces or torques on the first or the second cover member along a circumference of the first or the second cover member so as to generate a controllable change of curvature of the first or the second cover member.

The sliding contact arranged to allow displacement of the distal surface or the proximal surface relative to the one or more actuators is according to the invention.

According to an embodiment, the proximal surface and/or the distal surface are inwardly curved when seen from the eye.

According to an embodiment, the one of the first and second transparent cover member on which the one or more actuators act, is bendable by the generated forces or torques of the one or more actuators, and the other of the first and second transparent cover member is shaped to provide a static optical correction.

According to the invention the one of the first and second transparent cover member on which the one or more actuators act, is supported on the distal surface or the proximal surface, respectively, by a sliding contact which allows a displacement of the distal surface or the proximal surface along the surface relative to the actuator.

According to an embodiment, the spectacle lens is arranged so that the non-fluid body is able to expand unconstrained in an annular volume located between the first and second transparent cover members and surrounding the non-fluid body. According to an embodiment, the spectacle lens is arranged so that light from the exterior travelling through the spectacle lens towards an eye is refracted through a sandwich structure consisting of the first and second transparent cover members and the non-fluid body, optionally including optical coatings on the distal surfaces of the first and second transparent cover members. Advantageously, the simple design of the spectacle lens provides a solution few components. According to an embodiment, at least one of the first and second transparent cover members has an initial curved shape so that the spectacle lens has a non-zero optical power when the one or more actuators provide a zero or minimum force on the first or second cover member.

According to an embodiment, at least one of the first and second transparent cover members has a concave or convex shaped portion abutting the non-fluid body.

According to an embodiment, the one or more actuators are controllable to generate at least two predetermined optical powers of the spectacle lens.

According to an embodiment, the spectacle lens is optimized to generate minimum optical errors at the at least two predetermined optical powers.

According to an embodiment, the one or more actuators are controlled via a control or power signal, where the control or power signal is determined as a function of measured data.

According to an embodiment, the one or more actuators are controlled via a control signal, where the control signal is determined as a function of an error between a desired optical power of the spectacle lens and measured data relating to the actual optical power.

According to an embodiment, the actuators are linear displacement motors capable of maintaining an achieved curvature of the first or the second transparent cover member in a non-powered state.

According to an embodiment, a minimum diameter of a line extending from one edge to an opposite edge and crossing a center point of the spectacle lens is <NUM>.

According to an embodiment, the sliding contact comprises one or more elastic elements connecting the one or more actuators with the distal surface and/or the proximal surface.

A second aspect of the invention relates to a spectacle comprising.

In general, the various aspects and embodiments of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

<FIG> shows a pair of spectacles <NUM> comprising two spectacle lenses <NUM> mounted in a spectacle frame <NUM>. The pair of spectacles <NUM> further comprises a power and control circuit <NUM>, which may be integrated in the frame <NUM>, for powering and controlling one or more actuators <NUM> arranged to generate forces acting on one or more of the lenses <NUM> in order to generate a controllable change of the optical power of the lenses <NUM>. The power and control circuit <NUM> and the actuators <NUM> are principally illustrated.

<FIG> shows a front view of one of the spectacle lenses <NUM>, and <FIG> shows a side view or cross-sectional view of the lens <NUM>.

The lens comprises a first transparent cover member <NUM>, and a second transparent cover member <NUM>. The first transparent cover member <NUM> is defined as the cover member which is located next to the eye <NUM>, when in use. Accordingly, the second cover member <NUM> is defined as the cover member which is located nearest the surroundings, i.e. the object space, when in use.

The outwardly facing surface of the first transparent cover member <NUM> is defined as a proximal surface <NUM> which faces the eye <NUM> when in use. The outwardly facing surface of the second transparent cover member <NUM> is defined as a distal surface <NUM> which faces the surroundings when in use.

The lens <NUM> comprises a transparent, deformable, non-fluid body <NUM> sandwiched between the first and second transparent cover members <NUM>, <NUM>. The non-fluid body <NUM> abuts the inwardly facing surfaces of the first and second cover members <NUM>, <NUM>.

The one or more actuators <NUM> are arranged to generate forces or torques on the first or the second cover member <NUM>, <NUM> along a circumference <NUM> of the first or the second cover member.

For example, the actuators <NUM> may be linear displacement actuators, such as linear piezoelectric motors, arranged to apply a displacement at several points, here four points are illustrated, along the circumference <NUM>.

The circumference <NUM> may located outside the transparent, deformable, non-fluid body <NUM> so that the non-fluid body <NUM> is surrounded by the circumference as illustrated. However, the circumference <NUM> could also be located within the extension of the non-fluid body <NUM>. The actuators <NUM> could also be located so that they act on the edge <NUM> of the first or second cover member <NUM>, <NUM>.

Thus, the circumference <NUM> is understood as a path which surrounds at least a portion of the non-fluid body, such as a portion which comprises the optical axis <NUM> or a center portion of the non-fluid body.

Other configurations where the actuators act on a frame or mount that transfer the force to the lenses <NUM> are also possible. In this case the force or torque from a single actuator could be distributed to the cover members <NUM>, <NUM>. The frame or mount could covert rotation of a rotational actuator into linear displacement.

The actuators <NUM> are arranged to generate the displacement along the circumference <NUM> in a direction normal or substantially normal to one of the surfaces, e.g. the proximal or distal surface <NUM>, <NUM>. Substantially normal, in this context, may imply deviations relative to the normal by up to e.g. <NUM>-<NUM> degrees. Other configurations where the actuators act on the edge <NUM>, e.g. an actuator comprising a tightening belt which at least partly circumscribes the edge <NUM>, are also possible. Thus, in such other configurations the actuators may be arranged to generate forces acting in the plane of the cover member <NUM>, <NUM>.

The action of the actuators, as described in more detail below, changes the curvature of the first or the second cover member dependent on the force, torque or displacement provided by the actuators. Thus, by controlling the actuators, the bending and thereby the optical power of the lens <NUM> can be controlled.

In order to enable the bending of the first or second membrane <NUM>, <NUM>, the one of the first and second membrane which is not in contact with the actuators <NUM>, may be supported by a portion of the spectacles frame <NUM>, i.e. so that the this first or second membrane is fixed to the frame <NUM>.

The example of <FIG> shows that the second membrane <NUM> is fixed to the frame <NUM>, <NUM> and that the first membrane <NUM> is connected to the one or more actuators <NUM>. In another example, the first membrane <NUM> is fixed to the frame <NUM>, <NUM> and the second membrane <NUM> is connected to the one or more actuators <NUM>.

It is also possible that the actuators are arranged to act on both the first and second membranes <NUM>, <NUM> so that both membranes are forced to bend by the action of the actuators <NUM>, possibly so that actuators on either side are controllable independently, i.e. so that the displacement/force applied on one of the cover members is independent of the displacement/force applied on the other.

An example of such a solution is illustrated in <FIG>, where the actuators are fixed to the frame <NUM>, <NUM> of the spectacles and the cover members <NUM>, <NUM> are fixed to the actuators.

<FIG> illustrates another actuator <NUM> embodied by one or more elements <NUM> arranged along the circumference <NUM>. For example, the actuator <NUM> may be embodied by a ring shaped actuator element <NUM> such as a ring shaped piezo element which is attached to the proximal and/or the distal surfaces <NUM>, <NUM> of the first and/or second cover member <NUM>, <NUM>.

The actuator <NUM> in the form of a ring shaped actuator such as a ring shaped piezoelectric element <NUM>, or a distribution of individual surface mounted elements <NUM>, is arranged centered at the optical axis <NUM> so that interior of the ring element <NUM> or distribution of elements <NUM> along the circumference <NUM> allows transmission of light. By supplying power signal to the elements <NUM>, the elements contracts or expands radially (e.g. in a plane perpendicular to the optical axis <NUM>), essentially rotation symmetric relative to the optical axis <NUM>. The generated contractile or expansive forces T are transferred to the cover members <NUM>, <NUM> and cause bending due to the torques generated by the forces T. The lenses <NUM> in <FIG> may be connected to the frame via the elements <NUM> as in <FIG>, e.g. when both of the cover members comprise elements <NUM>, or via the cover member as in <FIG> when this cover member does not have elements <NUM>.

The components of <FIG> are described in more detail in <FIG>.

The lens <NUM> defines an optical axis <NUM>. The optical axis can be seen as the axis that light propagates along from the object space towards the eye <NUM>, at least for some paraxial light rays. The plane or curved surfaces of the first and second transparent membranes <NUM>, <NUM>, such as the plane or curved proximal/distal surfaces <NUM>, <NUM>, may - on at least one surface point - define a plane or tangent plane which is normal to the optical axis <NUM>, or at least define a plane or tangent plane which makes an acute angle with a plane which is normal to the optical axis <NUM>. Thus, the planes of the first and second transparent membranes <NUM>, <NUM> generally extends along a direction perpendicular to the optical axis <NUM>.

The transparent deformable, non-fluid lens body <NUM> is preferably made from an elastic material. Since the lens body is non-fluid, no fluid-tight enclosure is needed to hold the lens body, and there is no risk of leakage. In a preferred embodiment, the lens body is made from a soft polymer, which may include a number of different materials, such as silicone, polymer gels, a polymer network of cross-linked or partly cross-linked polymers, and a miscible oil or combination of oils. The elastic modulus of the non-fluid lens body may be larger than <NUM> Pa, thereby avoiding deformation due to gravitational forces in normal operation. The refractive index of the non-fluid lens body may be larger than <NUM>. The non-fluid body <NUM> may have a refractive index which is equal, substantially equal or close to the refractive index of the transparent cover members <NUM>, <NUM> in order to reduce reflections at the boundaries of the non-fluid body <NUM>.

The transparent cover members <NUM>, <NUM> may be made from a large number of different materials, such as acrylics, polyolefins, polyesters, silicones, polyurethanes, glass and others. At least the one of the first and second cover members <NUM>, <NUM> which is arranged to be deformed by the actuators, has a stiffness and thickness suitable to enable bending by actuation of the actuators <NUM>. In general, the material of the first and/or the second cover member <NUM>, <NUM> may be formed in a material having a Young's modulus in the range between <NUM> MPa and <NUM> GPa to provide the necessary stiffness. For example, Young's modulus for borosilicate glass is <NUM> GPa, and <NUM> GPa for fused silica glass.

The bending of the first and/or second cover members <NUM>, <NUM> is at least partly due to radially varying reaction forces from the non-fluid lens body <NUM> which affects the Sag of the cover members <NUM>, <NUM> and thus the optical power instead of just vertically compressing the lens body with no change in Sag. A full explanation of the effect of the lens body <NUM> on the curvature of the cover members is described in <CIT>. The material of the non-fluid lens body <NUM> is substantially incompressible. This incompressibility is at least partly responsible for the capability of bending the first and/or second cover members <NUM>, <NUM> in a shape which provides the effect of an optical lens.

Like traditional spectacle lenses, the lens <NUM> may comprise coatings such as antireflection coatings applied on the proximal surface <NUM> and/or the distal surface <NUM>.

The transparent cover members <NUM>, <NUM> are generally slab-shaped and may have curved or plane surfaces or a combination thereof. The slab-shaped cover members comprises first and second surfaces, e.g. the distal surface <NUM> and the inner surface <NUM>, and an edge, where the curvature extends along at least one direction on at least one of the surfaces. Thus, the transparent cover members <NUM>, <NUM> may be curved along only one direction or along two directions. Alternatively, one or both of the first and second surfaces may be plane. For example, one or both of the cover members <NUM>, <NUM> may constitute a plano-convex or plano-concave lens.

The thickness of the cover member which is arranged to be bend by the actuators may be in the range from <NUM> to <NUM> or up to <NUM> although other thicknesses are also possible.

The spectacle lenses <NUM> may have a minimum diameter defined by a line extending from one edge to an opposite edge and crossing a center point of the spectacle lens of <NUM>. the minimum diameter of the lenses <NUM> are generally larger than <NUM>. Typical diameters of lenses <NUM> are in the range from <NUM> to <NUM>.

<FIG> illustrates the principle of controlling the curvature of one of the first or the second cover members <NUM>, <NUM>. In <FIG>, the first cover member <NUM> has a curved surface implying that the lens can generate a non-zero optical power.

The deformations and expansions shown in <FIG> are largely exaggerated. Furthermore, the first cover member <NUM> is illustrated with an outwardly curved bending (see from the eye side), whereas an inwardly curved shape would be more typical. However, both outwardly and inwardly curved bending shaped are feasible for different sight corrections.

The curvature of the first cover member <NUM> in <FIG> may be due to the forces provided by the actuators <NUM>. Alternatively, the curvature of the first cover member <NUM>, may be a pre-shaped curvature. Thus, the first cover member <NUM> may have an initial curvature, i.e. a curvature present in the absence of actuator forces, implying that the spectacle lens <NUM> has a non-zero optical power when the one or more actuators provides a zero or minimum force on the first cover member <NUM>, or the second cover member <NUM>, e.g. in a non-powered state of the actuators.

<FIG> shows a further bending of the first cover member <NUM> due to a displacement, e.g. in direction of the optical axis, of the actuators <NUM>. The further bending changes the optical power of the lens <NUM>.

Due to the further bending of the first cover member <NUM> the volume between the first and second membranes <NUM>, <NUM> reduces implying that the incompressible non-fluid body <NUM> expands radially away from the optical axis as illustrated in <FIG> where the boundary of the non-fluid body <NUM> has expanded from the boundary indicated with dotted lines to the boundary <NUM> indicated with solid lines.

The non-fluid body <NUM> must be able to expand unconstrained, substantially unconstrained or at least with a low resistance, in order not to create deviations of the bending shape from a desired bending shape. Such deviations could result in optical errors such as wavefront aberrations. Accordingly, the spectacle lens <NUM> may comprise an annular volume <NUM> located between the first and second transparent cover members <NUM>, <NUM> and surrounding the non-fluid body wherein the non-fluid body <NUM> is able to expand unconstrained. The annular volume <NUM> may be an air-filled volume which may be in direct connection with the surroundings so that air is able to flow freely or substantially freely between the annular volume <NUM> and the surroundings.

<FIG> indicates a point A on the first cover member <NUM>. <FIG> shows that the point A has moved to the right relative to the left-side actuator <NUM> due to the increased bending of the first cover member <NUM>. Accordingly, as the bending of the first or second cover member <NUM>, <NUM> changes, positions A on the proximal surface <NUM> or the distal surface <NUM> translates radially relative to the optical axis <NUM>, e.g. in a direction <NUM> perpendicular to the optical axis <NUM> for the illustrated cross-sectional view.

To avoid stresses in the first or second cover member, the spectacle lens <NUM> comprises a sliding contact <NUM> as principally illustrated in <FIG>. The one of the first and second transparent cover member which is arranged to be bend by the one or more actuators, is supported or mechanically engaged on the distal surface/proximal surface <NUM>,<NUM> by the actuator <NUM> or the part of the actuator <NUM> which engages the cover member via the sliding contact <NUM>.

The sliding contact <NUM> may be embodied by a low friction contact between the actuator <NUM> and the distal surface/proximal surface <NUM>,<NUM>. The low friction contract may be realized by pairs of low friction materials, i.e. the material of the contacting part of the actuator <NUM> should provide low friction or sufficiently low friction relative to the transparent material of the cover member <NUM>, <NUM>. Examples comprise polyethylene and other plastic materials.

The sliding contact <NUM> ensures that a given point on the proximal/distal surface <NUM>,<NUM> can be displaced along that surface relative to the contact part of the actuator <NUM>.

The sliding contact <NUM> is configured to enable displacement of the distal surface <NUM> or the proximal surface <NUM> along the surface relative to the part of the actuator <NUM> which engages said surface. Furthermore, the sliding contact should provide a rigid, i.e. stiff, connection in a direction normal to the surface at the supported location or in a direction of the displacement of the actuator <NUM> so that actuator displacements are directly transferred to the cover member <NUM>, <NUM>.

<FIG> shows another configuration of the sliding contact <NUM>, wherein the sliding contact <NUM> is embodied by an elastic element <NUM> arranged between the actuator <NUM> and the distal surface/proximal surface <NUM>,<NUM> and connecting the actuator <NUM> with the distal surface/proximal surface <NUM>,<NUM>.

The elastic element <NUM> is arranged to deform elastically in response to a relative displacement between the actuator <NUM> and the distal surface/proximal surface <NUM>, <NUM>, such as in response to a radial displacement there between, e.g. a radial translation in the direction <NUM> perpendicular to the optical axis <NUM>.

The stationary xyz coordinate system is defined relative to an initial location of the elastic element <NUM>, e.g. when the elastic element <NUM> is in a non-deformed state. In this example, the z axis is parallel with the optical axis <NUM>.

In the illustration to the left, the first transparent cover member <NUM> (could also have been the second transparent cover member <NUM>) has an initial curvature, which may be due to a pre-shaped curvature or due to an initial displacement. A contact point <NUM> on the first transparent cover member <NUM>, at the interface between the elastic element <NUM> and the first transparent cover member <NUM> has xz coordinates x0,z0.

In the illustration to the right, the actuator <NUM> has been controlled to move or extend its piston or other displacement element by a distance ΔL1 along the z axis. The displacement generates a bending or additional bending of the first transparent cover member <NUM> so that the contact point <NUM> moves from x0,z0 to x1,z1 due a radial displacement of the contact point <NUM> towards the optical axis and due to a displacement along the z axis.

Due to the bending of the first transparent member <NUM>, the surface at the interface between the elastic element <NUM> and the first transparent cover member <NUM> is rotated about the y axis, i.e. in general around an axis which is tangent to the path <NUM> encircling the optical axis <NUM>.

As illustrated, the elastic element <NUM> is configured to deform elastically in the radial direction, here shown along the x-axis, in response to the relative radial displacement between the first transparent cover member <NUM> member and the actuator <NUM>.

Furthermore, the elastic element <NUM> is configured to deform elastically in response to the torque Ty acting around the y-axis, or the tangent axis. The torque Ty is generated due to the bending of the first transparent cover member <NUM> which includes a rotation around the y-axis, or in general due to the relative displacement between the first transparent cover member and the actuator displacement element.

Preferably, the elastic element <NUM> has a low stiffness in response to deformations in the radial direction and in response to rotations such as rotations about the tangent axis being tangent to the path <NUM>, the y axis in this view. A low stiffness is preferred in order to allow the first transparent cover member <NUM> to bend without being exposed to surface stresses which could affect the curvature of the first transparent cover member <NUM> inappropriately, so that the modified curvature leads to increased wave front errors or other bending deviations. The undesired stresses would be due to e.g. forces and torques from the elastic element <NUM> acting in the radial direction and around the tangent axis.

On the other hand, it is preferred that the elastic element has a high stiffness in the direction of displacement of the actuator <NUM>, i.e. along the z-axis or along the optical axis <NUM>, in order to transfer the actuator displacement to the cover member <NUM>, <NUM>.

The elastic element <NUM> can be defined as a structure which has a first portion <NUM> (e.g. the surface of the elastic element contacting the cover member <NUM>, <NUM>) fixed to the first or second transparent cover member <NUM>, <NUM> and a second portion <NUM> (e.g. the surface contacting the actuator <NUM>) fixed to the actuator <NUM> or displacement element thereof. The first and second portions <NUM>, <NUM> are connected elastically so that they are able to displace elastically relative to each other, e.g. in the radial direction to towards the optical axis <NUM>. The elastic element <NUM> may be monolithically manufactured from an elastic material such as silicon, polymer, metal, plastic and other materials. In an example, the elastic element <NUM> is formed from an adhesive applied to connect the actuator <NUM> with the transparent cover member.

Accordingly, the elastic element <NUM> which embodies the sliding contact <NUM> enables displacement of the first or second transparent cover member <NUM>, <NUM>, such as the contact point <NUM>, relative to the part of the actuator <NUM> which engages the cover member, in response to the bending of the cover member.

According to another example, the elastic element <NUM> is configured as a spring element arranged between the actuator <NUM> and the distal surface/proximal surface <NUM>,<NUM>. For example, the spring element may be configured as a flexure element having relative low stiffness in the radial direction, a relative low rotational stiffness about the tangent axis, but a relative high stiffness along the optical axis.

<FIG> principally illustrates the elastic element <NUM> comprising a spring element <NUM>. The illustration to the left illustrates the elastic element <NUM>, or a part of the elastic element, comprising the spring element <NUM>, in a state where the actuator <NUM> does not generate a force, i.e. F=<NUM>. Thus, the first transparent cover member <NUM> is in a state where its curvature is not changed by the actuators.

In the illustration to the right, the actuator displacement element has been activated to cause a z-axis displacement of ΔL1. The z-axis displacement generates a non-zero equilibrium force F1 (i.e. in the stationary bending state of the cover member) in the z-direction due to the reaction forces caused at least in part by the bending of the first transparent cover member <NUM>. The z-axis displacement generated by the actuator <NUM> causes the first transparent cover member <NUM> to bend as exaggeratedly shown. The bending causes, besides the ΔL1 z-axis displacement, a radial displacement of the first portion <NUM> (here a displacement to the right) along the x-axis and a rotation of the first portion <NUM> about the y-axis.

It is understood that the sliding element contact <NUM> may comprise both a spring element <NUM> and an elastic material, such as an elastic adhesive arranged between the first and/or second portion <NUM>, <NUM> and the surface of the first or second transparent cover member <NUM>, <NUM>.

Thus, in general, the examples of the sliding element contact <NUM> embodied by an elastic element <NUM> and/or by a low friction contact provides the same sliding response to the actuator <NUM> generated displacement, namely radial displacement of a contact point <NUM>, A (<FIG>, <FIG>, respectively) and a rotation to support the bending of the first or second cover member <NUM>,<NUM> and transfer of the actuator displacement to the first or second cover member.

In a possible configuration of the first or second cover member <NUM>, <NUM>, the first or second cover member comprises a stiffener element such as stiffener ring (not shown). The stiffener element may be annularly shaped so that it follows the circumference <NUM> and may e.g. by glued onto the distal/proximal surface <NUM>,<NUM> of the cover member <NUM>, <NUM>. The stiffener element of may be made of a metal or other stiff material. In this configuration, the contact portion of the actuator <NUM>, i.e. the portion arranged to make contact with the cover member <NUM>, <NUM>, will contact the stiffener ring, e.g. via the sliding contact <NUM>. Clearly, the radial extension of the stiffener element should be large enough to accommodate radial translations of the surface of the cover member <NUM>,<NUM> due to bending.

<FIG> shows an example where both the proximal surface <NUM> of the first transparent cover member <NUM> and the distal surface <NUM> of the second transparent cover member <NUM> are inwardly curved (bulges inward or is concave) when seen from the eye. The inwardly curved shape may be preferred for optometrical reasons or to provide an attractive design of the spectacles. It is also possible that only one of the proximal surface <NUM> of the first transparent cover member <NUM> and the distal surface <NUM> of the second transparent cover member <NUM> are concavely shaped when seen from the eye <NUM>. The inwardly curved shape of the one of the cover members <NUM>,<NUM> which is arranged to be bend by the actuators <NUM> may be due to a pre-shaping of the cover member. Accordingly, the curvature of inwardly curved shape may be altered by the actuators <NUM> to provide variable optical power.

<FIG> also shows that the curvatures of the proximal surface <NUM> and the inner surface <NUM> of the first cover member <NUM> are different and similarly that the distal surface <NUM> and the inner surface <NUM> of the second cover member <NUM> are different. The different curvatures of a given cover member <NUM>, <NUM> provides an optical power or optical correction as used in traditional spectacle lenses. It is also possible that only one of the first and second cover members has different curvatures of its surfaces. For example, the one of the first and second transparent cover members <NUM>, <NUM> which is not arranged to be bend by the actuators may be shaped to provide a static optical correction. The static optical correction may include correction of myopia, hyperopia, astigmatism and others.

<FIG> shows an example where the one of the first and second transparent cover members <NUM>, <NUM> which is not arranged to be bend by the actuators has a convex portion <NUM>, e.g. centered at the optical axis, which forms part of the inner surface <NUM>. The convex portion abuts the non-fluid body <NUM>.

In general, anyone or both of the of the first and second transparent cover members <NUM>, <NUM> may be configured with concave or a convex shaped portion <NUM> forming part of the inner surface <NUM> and abutting the non-fluid body <NUM>. For example, the concavely shaped portion <NUM> provides a dome shaped feature which advantageously provides mechanical support to the opposite cover member and therefore assists in controlling the bending. The shape of the dome can be designed in such a way that it acts at least partly as a die for the shape of the opposite member cover member. Further, the dome or convex shaped protrusion may enable larger deformation of opposite cover member.

<FIG> principally illustrates a relationship, expressed by the curve <NUM>, between a control or power signal <NUM> applied to the actuators <NUM> and the resulting optical power <NUM>. The curve <NUM> shows that the optical power may be changed continuously from a minimum value to a maximum value. The lenses <NUM> may be configured to provide a change of up to <NUM>, up to <NUM> or possibly up to <NUM> diopters from the minimum optical power to the maximum optical power. Accordingly, the optical power may be continuously adjusted according to the need the eyes of the user.

In other situations, a continuous change of the optical power may not be preferred, e.g. in order to provide spectacles <NUM> that resembles traditional spectacles. Accordingly, the control system <NUM> may be configured to shift between predetermined optical powers of the spectacle lenses <NUM>. <FIG> shows that the lens <NUM> can be controlled to provide two predetermined optical powers <NUM>, <NUM> by controlling the actuators with two values <NUM>, <NUM> of the control or power signal. The values <NUM>, <NUM> may be predetermined, determined as a function of other data or determined via a feedback function. Accordingly, the one or more actuators may be controllable to generate at least two predetermined optical powers of the lens <NUM>.

<FIG> illustrates an optical error <NUM> such as a wavefront distortion error or an aberration error, expressed by curve <NUM>, as a function of the control or power signal <NUM>. As illustrated, the optical error <NUM> is minimized for two values of the control or power signal <NUM> corresponding to two values of the optical power <NUM>. The optical error <NUM> may be minimized for two or more optical powers by optimizing the preshaped curvatures of the first and second cover members <NUM>, <NUM> to provide minimum optical errors at the desired predetermined optical powers <NUM>, <NUM>.

The control or power signal, i.e. a control signal which is indirectly used for controlling the actuators or a power signal directly used for powering the actuators, may be predetermined, i.e. so that a predetermined relationship between one or more values of the control or power signal and corresponding optical powers <NUM> is used. This relation ship may be stored in a memory comprised by the control circuit <NUM>.

Alternatively, since the resulting optical power may depend on various factors such as temperature, history of usage or age of the actuators and others parameters, the control or power signal may be determined as a function of measured data such as measured temperature, measured capacity in case of actuators <NUM> based on piezoelectric elements, measured change of displacement amplitudes over time and others.

It is possible to configure the spectacles <NUM> with a distance sensor capable of measuring the distance between the lenses <NUM> and an object at which the user of the spectacles <NUM> is gazing. Such sensors may be time-of-flight sensors or other. In this case, the control or power signal may be determined as a function of an error between a desired optical power of the spectacle lens and measured data relating to the desired actual optical power such as the measured distance. Eye-tracking can be implemented in the spectacles to follow gaze direction. Such eye-tracking may be used in combination with the distance sensor to determine what distance should be measured and, therefore, the correctly determine the distance and the relevant optical power.

The actuators <NUM> may be linear displacement motors such as linear piezoelectric motors or electromagnetic linear motors. Piezoelectric motors may be advantageous since they are capable of maintaining an achieved displacement of the linear output member when power is not supplied to the motor. Thus, the curvature of the first or the second transparent cover member <NUM>, <NUM> can be maintained in a non-powered state, i.e. when power is not supplied to the motor. This advantageous reduced the power consumption, since power is mainly needed when the optical power is changed.

Claim 1:
A spectacle lens (<NUM>) comprising
- a first transparent cover member (<NUM>),
- a second transparent cover member (<NUM>), wherein the first cover member comprises a proximal surface (<NUM>) arranged to face the eye and the second cover member comprises a distal surface (<NUM>) arranged to face the surroundings when in use,
- one or more actuators (<NUM>) arranged to generate forces or torques on the first or the second cover member (<NUM>, <NUM>) along a circumference (<NUM>) of the first or the second cover member so as to generate a controllable change of curvature of the first or the second cover member, wherein the actuators are arranged to generate a displacement along the circumference in a direction normal or substantially normal to the proximal surface or the distal surface,
- a transparent, deformable, non-fluid body (<NUM>) sandwiched between the first and second transparent cover members,
- a sliding contact (<NUM>), wherein
- the one or more actuators (<NUM>) are mechanically engaged with the proximal surface or the distal surface via the sliding contact (<NUM>), wherein the sliding contact is configured to enable displacement of the distal surface or the proximal surface along the distal or proximal surface relative to the actuator and wherein the sliding contact is arranged to provide a stiff connection in a direction normal to the proximal or distal surface at the engagement location, or in the direction of the displacement of the actuator, so that the actuator displacement can be directly transferred to the cover member (<NUM>, <NUM>).