Patent Description:
Soft contact lenses comprising electrically-switchable liquid crystal are known. The liquid crystal is typically retained in a liquid crystal cell in a cavity. When the contact lens is placed on the cornea of a wearer, the posterior surface of the contact lens conforms to the shape of the cornea, which results in distortion of the liquid crystal cell. The distortion can be exacerbated by gravity and eye-lid pressure when liquid crystal containing soft contact lenses are located on an eye. Such distortion is undesirable because it negatively affects the optical properties of the contact lens, such as by causing blurry vision or by increasing optical aberrations of the contact lens. <CIT> describes a contact lens with a diffractive element, wherein a spacer is placed on the central peak of the diffractive element and a spacer is placed on an outer peak of the diffractive element. <CIT>describes a lens comprising a Fresnel lens structure and spacers located in grooves of the Fresnel lens structure.

It is desirable to provide a soft contact lens that has a liquid crystal optic component and that inhibits the distortion of the liquid crystal cell and/or reduces the effect of distortion of the liquid crystal cell on optical performance of the contact lens.

The present invention provides, according to a first aspect, an electrically-switchable flexible ophthalmic lens for conforming to the eye of a user according to claim <NUM>. Further optional features of the lens are described in claims <NUM> to <NUM>.

The applicant has surprisingly discovered that the provision of support locations in the form of a ring is particularly effective at maintaining the cell spacing, even in the event that the liquid crystal cell is subject to a deforming force such as occurs when the lens is placed onto the cornea of a wearer.

Optionally, substantially all of the support members are arranged such that the support locations form one of the rings. In this case, there may be substantially no support locations that do not form one of the rings, but there may be a perimeter support as mentioned below.

Those skilled in the art will realise that "ring" does not mean that the ring is perfectly circular. In this connection, each of the support locations forming a respective ring may be within <NUM>% of the mean distance between the centre of the liquid crystal cell and the support locations forming the ring. Each of the support locations forming a respective ring may optionally be within <NUM>% of the mean distance between the centre of the liquid crystal cell and the support locations forming the ring, and optionally within <NUM>%, optionally within <NUM>%, optionally within <NUM>% and optionally within <NUM>% of the mean distance between the centre of the liquid crystal cell and the support locations forming the ring.

The liquid crystal cell optionally comprises a perimeter support configuration to maintain a perimeter gap thickness at a perimeter of the liquid crystal cell.

The liquid crystal cell has a cord radius, w. The cord radius may be defined by the perimeter support configuration. Those skilled in the art will realise that the liquid crystal cell may be curved. In that case, the liquid crystal cell half-width may be measured along a chord. The liquid crystal cell may optionally comprise a disc, spherical cap or distorted spherical cap of liquid crystal. For example, the perimeter support configuration may optionally be in the form of a ring. For example, the perimeter support configuration may optionally be annular.

The support locations form two, and only two, rings concentric with a centre of the liquid crystal cell. The mean distance between the centre of the liquid crystal cell and the support locations forming the first, inner, ring is optionally approximately the same as the mean distance between the support locations forming the first ring and the support locations forming the second, outer, ring.

At least one and optionally each ring may be substantially annular. The annular support configuration may comprise an annular support member, the annular shape of the support member defining the annular shape of the support configuration. The annular support member may comprise two semi-annular support members, the two semi-annular support members being arranged to define the annular ring. The annular ring may be defined by a plurality of arcuate support members. The annular ring may be defined by a plurality of "point" support members (such as posts or spheres).

Each support location forming the second ring may optionally be located from <NUM>. 56w to <NUM>. 70w, and optionally from <NUM>. 60w to <NUM>. 68w from the centre of the liquid crystal cell.

Each support member may be arranged to contact the first and second inner surfaces to maintain the cell gap thickness by providing support at a support location within the cell. In this case, the support members may be located between the first and second inner surfaces.

A centre of the liquid crystal cell, in plan view, may be the physical centre of the cell or may form a centre of the support configurations. The centre may be defined as an axis.

At least one and optionally each ring may be formed by more than one support member.

At least one and optionally each ring may be formed by three or more support members, optionally four or more, optionally six or more, optionally eight or more, optionally ten or more and optionally <NUM> or more support members.

If a ring is formed by more than one support member, the support members may optionally be spaced uniformly within the ring. For example, the distance between adjacent support members forming a respective ring may be approximately the same.

Each support member may have any suitable shape. For example, a support member may be a post, a sphere, a cylinder, an ellipsoid, an ovoid or arcuate.

A ring may comprise support members of mutually different shapes, but may optionally comprise support members of the same shape, and optionally of the same size.

If a support member is arcuate, then the arc may be a circular arc or a non-circular arc.

The angle of arc of an arcuate support member may be from <NUM> degrees to <NUM> degrees, typically depending on the number of support members that make-up a respective support configuration. For example, if a respective ring is formed by <NUM> or more arcuate support members, the angle of arc of each support member may optionally be from <NUM> degrees to <NUM> degrees, optionally from <NUM> degrees to <NUM> degrees and optionally from <NUM> degrees to <NUM> degrees. If a ring is formed by a single (i.e. one and only one) arcuate support member, the angle of arc may optionally be at least <NUM> degrees, optionally at least <NUM> degrees and optionally from <NUM> to <NUM> degrees. If a ring is formed by two (and only two) arcuate support members, then the angle of arc of each arcuate support members may optionally be from <NUM> to <NUM> degrees. A support member may be provided with one or more recess or aperture for the passage of liquid crystal therepast or therethrough. For example, if a support member is elongate, such as may be the case if the support member is semi-annular, or if the support member is annular, then in the absence of any such recess or aperture, the support member may provide a barrier to the flow of liquid crystal, which, in certain circumstances, may be undesirable. A support member may be provided with a plurality of recesses or apertures for the passage of liquid crystal therepast or therethrough.

The one or more support members may comprise a polymer, such as polydimethylsiloxane (PDMS). The one or more support members may comprise a material having a Young's modulus of from <NUM> to 5000kPa, optionally of from <NUM> to 2000kPa and optionally of from <NUM> to 1000kPa.

The cell gap thickness may be substantially the same across the liquid crystal cell when the lens is undeformed. Alternatively, the cell gap thickness may not be the same across the liquid crystal cell when the lens is undeformed. In this case, the cell gap thickness will depend on position within the liquid crystal cell. For example, if the ophthalmic lens comprises a so-called meniscus lens, then one of the first and second inner surfaces is typically convex and the other concave, the cell gap thickness at any point in the liquid crystal cell being determined by the curvature of the convex and concave surfaces. For example, if the liquid crystal cell comprises a Fresnel lens structure, the cell gap thickness at a particular point in the liquid crystal cell may depend on the height of the Fresnel lens structure at that point in the cell.

The maximum cell gap thickness (the largest spacing between first inner surface and second inner surface in the undeformed cell) may optionally be at least <NUM>, optionally at least <NUM>, optionally at least <NUM>, optionally at least <NUM> and optionally at least <NUM>. The maximum cell gap thickness may optionally be no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM> and optionally no more than <NUM>. The maximum cell gap thickness may optionally be from <NUM> to <NUM> and optionally from <NUM> to <NUM>.

The greatest dimension, such as a width or diameter (chord diameter), of the liquid crystal cell may optionally be no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM> and optionally no more than <NUM>. The greatest dimension of the liquid crystal cell may optionally be at least <NUM>, optionally at least <NUM> and optionally at least <NUM>.

The greatest dimension, such as the width or diameter (chord diameter), of the ophthalmic lens may optionally be no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM>, optionally no more than <NUM> and optionally no more than <NUM>. The greatest dimension of the ophthalmic lens may optionally be at least <NUM>, optionally at least <NUM>, optionally at least <NUM> and optionally at least <NUM>. In some embodiments, the diameter of the ophthalmic lens is between <NUM> and <NUM>.

At least one, and optionally each, of the first inner surface and the second inner surface are optionally provided with one or more surface treatments for aligning the liquid crystal. For example, the one or more surface treatments may comprise one or more alignment layers. At least one, and optionally each, alignment layer may comprise a polymer, such as an organic polymer, or an evaporated inorganic material, such as silicon oxide. Such polymers may have been at least partially oriented by applying a shear force to the surface of the polymer, for example, by brushing the surface of the polymer. Such polymers typically cause the liquid crystal to adopt a particular and desired orientation. For example, the director of the liquid crystal adjacent to the polymer may have a preferred in-plane orientation. Furthermore, the liquid crystal may have a low pre-tilt close to the polymer (for example, no more than <NUM>°, optionally no more than <NUM>° and optionally no more than <NUM>°). One or more surface treatments may orient the liquid crystal in a high pre-tilt orientation (for example, a pre-tilt of no less than <NUM>°, optionally no less than <NUM>°, optionally no less than <NUM>° and optionally no less than <NUM>°). The surface treatment may orient the liquid crystal in a substantially homeotropic alignment, with the director substantially perpendicular to the first and second inner surfaces.

The surface treatments on the first and second inner surface are typically chosen to confer a particular alignment on the liquid crystal. For example, the surface treatment of the first surface and second surface may be arranged so that the liquid crystal is in a twisted nematic arrangement.

The liquid crystal cell may comprise a first substrate and a second substrate for providing support to the liquid crystal cell. The first and second substrates are typically flexible. The liquid crystal cell may be flexible.

One or both of the first and second substrates may be provided with an electrically-conductive layer for addressing the liquid crystal in the cell. The electrically-conductive layer may comprise any suitable electrically-conductive material, such as indium-tin oxide (ITO). The electrically-conductive layer is typically suitably transparent to allow the lens to function as a lens. A non-conductive layer may be provided over the respective electrically-conductive layer. The non-conductive layer may be located between an electrically-conductive layer and the respective surface treatment for aligning the liquid crystal (such as an alignment layer).

The liquid crystal may be any suitable liquid crystal such as those well-known to those skilled in the art, such as E7 from Merck.

The liquid crystal may optionally be in the nematic liquid crystal phase at typical operating temperatures, for example, at25°C. The liquid crystal may optionally be in the nematic phase from <NUM> to <NUM> and optionally from -<NUM> to <NUM>.

Those skilled in the art will realise that a liquid crystal phase other than the nematic phase may be used. For example, the liquid crystal may be in a smectic phase at typical operating temperatures.

The perimeter gap thickness may optionally be approximately the same as the maximum cell gap thickness, although this will depend on the nature of the ophthalmic lens.

Alternatively, the maximum cell gap thickness may be less than the perimeter gap thickness. This may be the case, for example, if the cell comprises a second layer of liquid crystal in addition to that between the first and second inner surfaces. In this connection, the liquid crystal cell may have a cell spacing between a third inner surface and a fourth inner surface with liquid crystal therebetween, the liquid crystal between the third and fourth inner surfaces being in substantially the same optic path as the liquid crystal between the first and second inner surfaces. The liquid crystal cell may comprise one or more spacers for maintaining the cell spacing between the third inner surface and the fourth inner surface. Optionally, each spacer is arranged to maintain the cell spacing by providing support at a support location within the cell. The one or more of the spacers may be arranged in a similar manner to the support members between the first and second inner surfaces. In this connection, substantially all of the spacers may be arranged so that the support locations form one or more rings concentric with a centre of the liquid crystal cell. For the avoidance of doubt, the cell spacing may be substantially the same across the liquid crystal cell. Alternatively, the cell spacing may not be the same across the liquid crystal cell. In this case, the cell spacing will depend on the position within the liquid crystal cell. For example, if the ophthalmic lens comprises a so-called meniscus lens, then one of the third and fourth inner surfaces is typically convex and the other concave, the cell spacing at any point in the liquid crystal cell being determined by the curvature of the convex and concave surfaces. For example, if the liquid crystal cell comprises a Fresnel lens structure, the cell spacing at a particular point in the liquid crystal cell may depend on the height of the Fresnel lens structure at that point in the cell.

Each spacer may contact the third and fourth inner surfaces to maintain the cell spacing.

The one or more rings may have those features described above in relation to the one or more rings used to maintain the cell gap thickness between the first and second inner surfaces.

The one or more spacers may have those features described above in relation to the one or more support members used to maintain the cell gap thickness between the first and second inner surfaces.

The ophthalmic lens may comprise any suitable arrangement for providing the desired optical effect. For example, the ophthalmic lens may comprise a Fresnel lens structure. Such a Fresnel lens structure may define the shape of one of the first and second surfaces. The liquid crystal disposed between the first and second surfaces may be switchable between a first and a second liquid crystal configuration, the difference in the refractive index between the liquid crystal and the material forming the Fresnel lens structure being less in one of the first and second liquid crystal configuration than in the other of the first and second liquid crystal configuration. In one of the first and second liquid crystal configurations, the difference in the refractive index between the liquid crystal and the material forming the Fresnel lens may be small such that the refractive index of the liquid crystal "matches" that of the material forming the Fresnel lens. Therefore, in one of the liquid crystal configurations (the one in which the refractive indices of the Fresnel lens material and the liquid crystal are not matched) the Fresnel lens refracts light as a lens, and in the other of the liquid crystal configuration (the one in which the refractive indices of the Fresnel lens material and the liquid crystal are "matched"), the Fresnel lens does not refract light as a lens, or refracts light significantly less.

The height of any support member will depend on the geometry of the Fresnel lens structure and the location of a support member relative to the Fresnel lens. For example, if a support member is located on a Fresnel lens crest or peak, then the height of the support member may typically be smaller than if the support member were to be located in a trough of a Fresnel lens structure.

The ophthalmic lens may comprise a meniscus lens, for example. One of the first and second surfaces is a convex surface and the other of the first and second surfaces is a concave surface. The curvatures of the first and second surfaces may be the same or different. For example, the curvature of the convex surface may be greater or lower than that of the concave surface. The cell gap thickness in such a meniscus lens is optionally different depending on the position within the liquid crystal cell. For example, in the centre of the meniscus lens, the cell gap thickness in the centre of the lens may be greater than at the periphery of the lens. Alternatively, the cell gap thickness at the periphery of the lens may be greater than at the centre of the lens. The heights of the support members would be selected to maintain those cell gap thicknesses. The ophthalmic lens may comprise more than one meniscus lens. For example, the ophthalmic lens may comprise a first meniscus lens, and a second meniscus lens arranged in the same optical path as the first meniscus lens.

The ophthalmic lens may comprise a gradient-index (GRIN) lens, for example. A GRIN lens comprises a lens in which the refractive index of the liquid crystal depends on the lateral position across the liquid crystal cell. The variation in refractive index across the liquid crystal cell is typically achieved by virtue of the liquid crystal molecules having different orientations at different positions across the liquid crystal cell. This is optionally achieved using different surface treatments of the first and/or second surfaces in different regions of the liquid crystal cell to achieve different pretilts of the liquid crystal molecules at and adjacent the first or second surfaces. In a GRIN lens, the cell spacing between the first and second surfaces may be substantially the same across the liquid crystal cell. Alternatively, the cell spacing not be substantially the same across the liquid crystal cell. When a switching voltage is applied, the orientation of at least some of the liquid crystal molecules in the GRIN cell will change, thereby changing the refractive index of the liquid crystal associated with the change of orientation. The ophthalmic lens may comprise more than one GRIN lens. For example, the ophthalmic lens may comprise a first GRIN lens, and a second GRIN lens arranged in the same optical path as the first GRIN lens.

The ophthalmic lens may be a contact lens.

The liquid crystal cell is provided for changing at least one optical characteristic of the ophthalmic lens, such as the focal length of the ophthalmic lens.

As mentioned above, the one or more support members are used to maintain a cell gap thickness. In order to do this, the one or more support members are typically attached to another part of the liquid crystal cell. For example, adhesive may be used to attach the one or more support members to another part of the liquid crystal cell. For example, adhesive may be used to attach one or more support members to one or both of the first and second inner surfaces.

As mentioned above, each support member is arranged to maintain a cell gap thickness. The maintenance of cell gap thickness is important to maintaining the optical properties of the ophthalmic lens. In this connection, the mean change in cell gap thickness across the liquid crystal cell may optionally be no more than <NUM>%, optionally no more than <NUM>%, optionally no more than <NUM>%, optionally no more than <NUM>% and optionally no more than <NUM>% when the ophthalmic lens is deformed by being placed on the eye of a user.

In accordance with a first merely illustrative embodiment, there is provided a flexible liquid crystal cell suitable for the lens in accordance with the first aspect of the present invention.

There is therefore provided a liquid crystal cell for changing at least one optical characteristic of an ophthalmic lens, and having a cell gap thickness between a first inner surface and a second inner surface, and comprising:.

The liquid crystal cell may therefore have the features described above in relation to the lens of the first aspect of the present invention.

In accordance with a second merely illustrative embodiment, there is provided an electrically-switchable flexible ophthalmic lens comprising a liquid crystal cell for changing at least one optical characteristic of the ophthalmic lens, and having a cell gap thickness between a first inner surface and a second inner surface, and comprising:.

The applicant has surprisingly discovered that the provision of support members that provide support locations in the form of two annular rings is particularly effective at reducing the deterioration of lens performance when the lens is placed on the cornea of a wearer. For the avoidance of doubt, there are substantially no support members that provide support locations outside the annular rings.

The liquid crystal cell optionally comprises a perimeter support configuration to maintain the cell gap thickness at a perimeter of the liquid crystal cell.

The lens of this second merely illustrative embodiment may comprise the features of the lens of the first aspect of the present invention.

In accordance with a third merely illustrative embodiment, there is provided a liquid crystal cell suitable for the lens in accordance with the second merely illustrative embodiment. In accordance with the third merely illustrative embodiment, there is therefore provided a liquid crystal cell for changing at least one optical characteristic, such as refractive power, of an ophthalmic lens, and having a cell gap thickness between a first inner surface and a second inner surface, and comprising:.

The liquid crystal cell of the third merely illustrative embodiment may comprise those features described above in relation to the first aspect of the present invention, and in relation to the first and second merely illustrative embodiments.

In accordance with a fourth merely illustrative embodiment, there is provided an electrically-switchable flexible ophthalmic lens comprising.

The applicant has discovered that a cell gap thickness in a liquid crystal cell in a flexible lens may be maintained using an arcuate support member. Furthermore, such arcuate support members may be used to define a ring of support locations within a liquid crystal cell which has proved to be useful in reducing the deleterious effects associated with cell deformation when a lens is placed on the eye of a wearer. The arc of an arcuate support member may be a circular arc or a non-circular arc.

The angle of arc of an arcuate support member may be from <NUM> degrees to <NUM> degrees. For example, if a plurality of support members are used in combination to define a ring of support locations in the liquid crystal cell, then the angle of the arc may optionally depend on the number of support members that form said ring. For example, if a respective ring is formed by <NUM> or more arcuate support members, the angle of arc of each support member may optionally be from <NUM> degrees to <NUM> degrees, optionally from <NUM> degrees to <NUM> degrees and optionally from <NUM> degrees to <NUM> degrees. If a ring is formed by a single (i.e. one and only one) arcuate support member, the angle of arc may optionally be at least <NUM> degrees, optionally at least <NUM> degrees and optionally from <NUM> to <NUM> degrees. If a ring is formed by two (and only two) arcuate support members, then the angle of arc of each arcuate support members may be from <NUM> to <NUM> degrees.

One or more of the arcuate support members may be provided with one or more recesses or apertures for the passage of liquid crystal therepast or therethrough. For example, if a support member is elongate, such as may be the case if the support member is semi-annular, or if the support member is annular, then in the absence of any such recess or aperture, the support member may provide a barrier to the flow of liquid crystal which, in certain circumstances, may be undesirable. A support member may be provided with a plurality of recesses or apertures for the passage of liquid crystal therepast or therethrough.

The lens of the fourth merely illustrative embodiment may comprise one or more features of the first aspect of the present invention, and of the first to third merely illustrative embodiments.

The present invention further provides a liquid crystal cell for use in the lens of the fourth merely illustrative embodiment.

In accordance with a fifth merely illustrative embodiment, there is therefore provided a liquid crystal cell having a cell gap thickness between a first inner surface and a second inner surface, the liquid crystal cell comprising one or more arcuate support members for helping to maintain the cell gap thickness.

The liquid crystal cell of the fifth merely illustrative embodiment may comprise one or more features of the first aspect of the present invention, and of the first to fifth merely illustrative embodiments.

It will, of course, be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the lens of the first aspect of the present invention may incorporate any of the features described with reference to the lens of the fifth aspect of the present invention and vice versa.

An example of a flexible lens in accordance with the present invention is shown schematically in <FIG> shows a schematic plan view of the lens and <FIG> shows a schematic cross-sectional view of the lens when situated on the cornea of a wearer. The electrically-switchable flexible ophthalmic lens <NUM> comprises a flexible liquid crystal cell <NUM> embedded within a lens body <NUM>. The lens body <NUM> has a shape typical of a soft contact lens. In the present case, the ophthalmic lens is a soft contact lens. The liquid crystal cell <NUM> has a cell gap thickness between a first inner surface <NUM> and a second inner surface <NUM> with liquid crystal <NUM> therebetween. The liquid crystal cell <NUM> is generally circular in shape, in plan view, such as in <FIG>. The lens body <NUM> comprises silicone. The lens body may comprise a hydrogel, a silicone hydrogel or a silicone elastomer. The liquid crystal cell <NUM> comprises a perimeter support configuration <NUM> to maintain a perimeter gap thickness at a perimeter of the liquid crystal cell. The perimeter support configuration <NUM> comprises an annular strip 6a of spacer sheet (e.g. Mylar®) of <NUM> microns thickness. The liquid crystal cell <NUM> comprises two support members, in the form of two annular supports <NUM>, <NUM> that are arranged to maintain the cell gap thickness by providing support at support locations within the cell. The support locations provided by the two annular support members <NUM>, <NUM> form two rings concentric with a centre of the liquid crystal cell <NUM>. The annular supports <NUM>, <NUM> may be made by any suitable method, for example, by using a source of suitable radiation (typically UV radiation) and a mask to control exposure of a radiation-sensitive material (such as a photopolymer).

A cross-sectional view of the lens can be seen in <FIG>. The lower surface L of the lens <NUM> conforms to the shape of the underlying eye, including the cornea. This causes deformation of the lens <NUM>, and thus causes deformation forces to be applied to the liquid crystal cell <NUM>. The use of two spaced annular support members <NUM>, <NUM> has proved to be particularly effective at reducing unwanted distortion of the liquid crystal cell <NUM> and unwanted changes in thickness of the liquid crystal layer when the lens is placed on the cornea of a wearer.

It is worth noting that the first inner <NUM> and second inner <NUM> surfaces are spaced apart by the perimeter support <NUM> and the two annular support members <NUM>, <NUM>. There are substantially no other spacers or support members that space-apart the first <NUM> and second <NUM> inner surfaces. Apart from the support at the perimeter of the liquid crystal cell, all of the support locations are located in the shape of two rings formed by the two annular support members <NUM>, <NUM>.

The first <NUM> and second <NUM> inner surfaces of the liquid crystal cell are provided with alignment polymers (not shown in <FIG>, but discussed below in relation to <FIG>) to confer alignment on the liquid crystal <NUM> so that the liquid crystal cell <NUM> has the desired optical properties for lens <NUM>. Electrically-conductive layers (also not shown in <FIG>, but discussed below in relation to <FIG>) are also provided to enable switching of the liquid crystal <NUM>.

A merely illustrative example of a flexible lens will now be described with reference to <FIG> is a schematic cross-section through part of lens <NUM> showing the positions of the support members that act to inhibit deformation of the liquid crystal cell. <FIG> is a schematic cross-section through lens <NUM> showing the arrangement of liquid crystal in the lens. Lens <NUM> is similar to that of lens <NUM> of <FIG> in that the lens <NUM> comprises a liquid crystal cell <NUM> embedded within a lens body <NUM>. The lens body <NUM> has a shape typical of a soft contact lens. The liquid crystal cell <NUM> is generally circular in shape, like the liquid crystal cell of <FIG>. Furthermore, as in the lens of <FIG>, the liquid crystal cell <NUM> is provided with two annular support members <NUM>, <NUM>. The two annular support members <NUM>, <NUM> are arranged to maintain the cell gap thickness between first <NUM> and second <NUM> inner surfaces by providing support at support locations within the cell. The support locations provided by the two annular support members <NUM>, <NUM> form two rings concentric with a centre of the liquid crystal cell <NUM>, the centre being denoted by axis C. The ring formed by support member <NUM> has a chord radius, r1, and the ring formed by support member <NUM> has a chord radius r2. As shown in <FIG>, r1 is about <NUM>. 3w, where w is the distance from the centre of the cell, C, to the edge of the liquid crystal cell, and r2 is about <NUM>. As in the lens of <FIG>, the lens <NUM> of <FIG> is provided with a perimeter support arrangement <NUM>. In this case, the perimeter support arrangement <NUM> comprises an annular perimeter of polymer having a Young's modulus of 500kPa. Support members <NUM>, <NUM> are also provided by a polymer having a Young's modulus of 500kPa.

The lens of <FIG> does differ in some material ways to the lens of <FIG>, however. Whereas the liquid crystal cell of <FIG> comprises one layer of liquid crystal, the liquid crystal cell <NUM> of <FIG> comprises two layers of liquid crystal <NUM>, <NUM>', each in the same optic path. Liquid crystal <NUM> is located between first <NUM> and second <NUM> inner surfaces, each of which is provided with alignment surfaces (not shown) that cause the liquid crystal molecules to align radially outwards from centre C, substantially parallel to inner surfaces <NUM>, <NUM> (though the molecules may have a small pre-tilt near the inner surfaces <NUM>, <NUM>). The arrows show the approximate alignment of the liquid crystal molecules. Liquid crystal <NUM>' is located between third <NUM> and fourth <NUM> inner surfaces. The third <NUM> and fourth <NUM> inner surfaces are provided with an alignment polymer (not shown) that has been brushed to align the liquid crystal molecules out of the plane of the figure. The alignment polymers in the left <NUM> and right <NUM> parts have been brushed in different directions to provide a pre-tilt in different directions in the left <NUM> and right <NUM> parts.

Electrically-conductive layers (not shown) are also provided to enable switching of the liquid crystal <NUM> and <NUM>'.

The applicant has investigated how the number and position of annular support members affects the performance of the lens when it is placed on a cornea of a wearer. In this connection, the applicant has discovered that the use of two supporting annular members has proved to be preferable to the use of one (and only one) supporting member.

The applicant has modelled the behaviour of the liquid crystal cell as shown in <FIG> to determine the optimum position of two annular support members, when the lens is deformed as it would be on the cornea of a wearer, taking into account the optical performance of the liquid crystal cell in an unswitched and switched state, using radially polarised light and circumferentially polarised light. In this connection, various parameters of the lens are as follows: <NUM> diameter lens, radius of curvature of top lens surface - <NUM>, radius of curvature of bottom lens surface - <NUM>, <NUM> thick lens made from PDMS having a modulus of 500kPa, half-width, w, of liquid crystal cell - <NUM>; thickness of liquid crystal <NUM> - <NUM> microns; thickness of liquid crystal <NUM>' - <NUM> microns; radius of curvature of liquid crystal cell - <NUM>; ne (extraordinary refractive index) - <NUM>; no (ordinary refractive index) - <NUM>.

The unswitched state corresponded to the application of no switching voltage. The switched state corresponded to a fully switched state in which the director of the liquid crystal is substantially parallel to the applied electric field.

The optical power of the liquid crystal cell as described above was investigated thus. The shape of the cornea's surface was defined as being the best <NUM>th order fit as defined in Lee et al. , BMC Ophthalmology, <NUM>, <NUM>:<NUM>. The bottom or posterior surface of the contact lens conforms to the cornea's surface, causing deformation of the liquid crystal cell. The position of the inner annular support, r1, was fixed at a value of between 0w and <NUM>. 45w, w being the chord radius of the liquid crystal cell, measured as shown in <FIG>. For each such fixed position of the inner annular support, r1, the position of the outer annular support, r2, was varied between <NUM>. 50w and <NUM>. For the avoidance of doubt, r1 and r2 are chord measurements. For each position of the inner annular support and the outer annular support, the optical power of the liquid crystal cell was simulated, in both a switched and unswitched state, for radially polarised and circumferentially polarised light. The variation in optical power across the liquid crystal cell was simulated, with a desire to minimise the variation in optical power across the liquid crystal cell for both radially and circumferentially polarised light, and with a desire to minimise the difference in optical power for radially polarised light and circumferentially polarised light.

<FIG> show the simulated optical power range (i.e. the variation in optical power across the lens) as a function of the position of the inner annular support and the outer annular support for <NUM> combinations of <NUM> conditions: light polarised radially or circumferentially, and for powered or unpowered liquid crystal cell. <FIG> shows the variation in simulated optical power range using light polarised circumferentially, with an unpowered liquid crystal cell. <FIG> shows the variation in simulated optical power range using light polarised circumferentially, with a powered liquid crystal cell. <FIG> shows the variation in simulated optical power range using light polarised radially, with an unpowered liquid crystal cell. <FIG> shows the variation in simulated optical power range using light polarised radially, with a powered liquid crystal cell. In each of <FIG>, the position of the inner annular support is denoted on the x-axis as a function of the chord radius, w, of the liquid crystal cell. The position of the outer annular support is denoted on the y-axis, as a function of the chord radius, w, of the liquid crystal cell. <FIG> show that the optimum combination of the positions of the inner and outer annular supports for all <NUM> cases was surprisingly determined to be about <NUM>. 3w for the inner support and about <NUM>. 7w for the outer support. With the annular supports in the optimised positions, the variation in optical power across the liquid crystal cell was found to be of the order of about <NUM>-2D (see <FIG>). In the absence of the annular supports, or with annular supports in different positions, it was found that the optical power range was higher and, in some cases, at least 4D. In the absence of the annular supports, the centre of the liquid crystal cell was found to collapse, with the periphery of the liquid crystal cell bulging.

Further data showing the performance of the lens is shown in <FIG>, which show optical power histograms in the powered (<FIG>) and unpowered (<FIG>) state for randomly polarised light. The x-axis shows the optical power in D, and the y-axis shows the number of uniformly distributed test rays, experiencing a range of optical power. A narrower histogram is desirable i.e. a greater proportion of the area of the lens being at the same power. The data show that the range of difference in power across the liquid crystal cell is small, with a <NUM>-<NUM>% range of about <NUM>.

In the liquid crystal cells of <FIG>, <FIG>, each ring is formed by an annular support member. An annular support member <NUM> is also shown schematically in <FIG>. However, such an annular support member <NUM> does not permit flow of liquid crystal therepast or therethrough unless there is a recess or aperture therein, and it may be desirable to permit flow of liquid crystal within the liquid crystal cell. In this connection, the support arrangements shown in plan view in <FIG> provide supporting ring arrangements but permit flow of liquid crystal.

<FIG> shows a ring <NUM> formed from a plurality of arcuate posts, two of which are labelled 107a, 107b. Each arcuate post is a circular arc and has an arc angle of about <NUM>°, and the arcuate posts are uniformly distributed about ring <NUM>. There is a gap of about <NUM>° between each arcuate post. The arcuate posts are provided between the first and second inner surfaces of the liquid crystal cell.

<FIG> shows a ring <NUM> formed from a plurality of posts, two of which are labelled 207a, 207b. The posts are circular cylindrical is cross-section. Once again, the arcuate posts are provided between the first and second inner surfaces of the liquid crystal cell.

<FIG> shows a ring <NUM> formed from two arcuate posts 307a, 307b. Each arcuate post is a circular arc and has an arc angle of about <NUM>°, with two small gaps between the arcuate posts.

The support members described above may be formed, for example, from a photo-sensitive material, such as a photopolymer. The photo-sensitive material may be exposed to suitable radiation using a radiation source and a mask, such exposure causing the exposed area to "harden" (or in some case, to "soften"). The "softened" or "unhardened" material can then be removed using a suitable solvent to leave the desired support members. The formation of support members using a mask is described in <CIT>.

A ring may also be formed, for example, by the selective placement of support members. For example, <NUM> micron spacer beads may be deposited on to a substrate, for example, using an automated deposition system to provide a ring of such spacer beads. For avoidance of doubt, there are gaps between the spacer beads.

<FIG> shows a schematic cross-section of part of an example of a liquid crystal cell in accordance with the present invention. The liquid crystal cell <NUM> has a cell gap thickness, G, between a first inner surface <NUM> and a second inner surface <NUM> with liquid crystal <NUM> therebetween. The liquid crystal cell comprises a perimeter support configuration (not shown) to maintain a perimeter gap thickness at a perimeter of the liquid crystal cell. The perimeter support configuration comprises four strips of <NUM> micron thick spacer sheet, each strip forming a side of a square, and providing a perimeter gap thickness of approx. <NUM> microns. In the present case, the cell gap thickness, G, is also approx. <NUM> microns. The liquid crystal cell <NUM> comprises a plurality of support members (now shown) in the form of <NUM> micron spacer beads, wherein each support member is arranged to maintain the cell gap thickness, G, by providing support at a support location within the cell. Substantially all of the support members are arranged such that the support locations form a first, inner ring, and a second, outer ring, concentric with a centre of the liquid crystal cell. The first and second inner rings are substantially as shown in relation to <FIG>, though the first and second inner ring of <FIG> are formed from a plurality of spacer beads with spaces therebetween, as opposed to a polymer annulus.

The liquid crystal cell <NUM> comprises a first flexible polymer substrate <NUM> and a second flexible polymer substrate <NUM>. Each substrate <NUM>, <NUM> is provided with an electrically-conductive layer <NUM>, <NUM> formed from indium-tin oxide. The electrically-conductive layers <NUM>, <NUM> are used to apply electrical signals to the liquid crystal <NUM> and change the orientation of the liquid crystal in order to change the optical characteristics of the liquid crystal cell. A barrier layer <NUM>, <NUM> may be provided on each electrically-conductive layer <NUM>, <NUM> to reduce surface roughness and to inhibit leaching of contaminants from the indium-tin oxide into the liquid crystal. A layer of alignment polymer <NUM>, <NUM> is provided on top of the barrier layer <NUM>, <NUM>. Each layer of alignment polymer <NUM>, <NUM> has been rubbed with a brush to align the alignment polymer. The liquid crystal <NUM> adjacent to the alignment polymer <NUM>, <NUM> is aligned in a particular direction as shown in <FIG>. Adjacent to first inner surface <NUM>, the liquid crystal director <NUM> is parallel to the plane of the image, whereas adjacent to second inner surface <NUM>, the liquid crystal director <NUM>' is perpendicular to the plane of the image. Furthermore, the liquid crystal molecules adjacent to the first inner surface and the second inner surface are approximately parallel to first and second inner surfaces (there is a small pre-tilt of about <NUM>-<NUM>°). The orientation of the liquid crystal molecules adjacent to the alignment polymers <NUM>, <NUM> are effectively fixed, and the viscoelastic properties of the liquid crystal means that the liquid crystal adopts a twisted configuration as shown in <FIG>. Application of an appropriate electric field will cause the orientation of the liquid crystal molecules to change, and therefore the optical properties of the liquid crystal to change, as is well-known to those skilled in the art.

Those skilled in the art will realise that the materials and thickness of the substrate, the electrically-conductive layer, the barrier layer and the alignment layer are chosen for satisfactory optical performance.

<FIG> shows a schematic cross-section through a further example of an embodiment of the liquid crystal cell in accordance with the present invention. The flexible liquid crystal cell <NUM> has a cell gap thickness G" between a first inner surface <NUM> and a second inner surface <NUM> with liquid crystal therebetween. The liquid crystal cell <NUM> comprises a perimeter support configuration <NUM> to maintain a perimeter gap thickness PG at a perimeter of the liquid crystal cell. The support configuration <NUM> comprises four strips of <NUM> micron thick spacer sheet, each strip forming a side of a square, and providing a perimeter gap thickness PG of approx. <NUM> microns. The liquid crystal cell <NUM> comprises a first, inner, annular support member <NUM> and a second, outer, support member <NUM>. Each support member <NUM>, <NUM> is arranged to maintain the cell gap thickness G by providing support at a support location within the cell. The support locations form one or more rings concentric with a centre of the liquid crystal cell <NUM>. Liquid crystal <NUM> is provided between the first <NUM> and second <NUM> inner surfaces.

Liquid crystal cell <NUM> comprises liquid crystal <NUM>' that is in the same optic path as liquid crystal <NUM>. The thickness of liquid crystal <NUM>' corresponds to the cell spacing G‴ between third <NUM> and fourth <NUM> inner surfaces. Cell spacing G‴ is maintained by spacers <NUM> and <NUM>. Spacer <NUM> is in the form of an inner annulus and spacer <NUM> is in the form of an outer annulus.

First inner surface <NUM> is supported by first substrate <NUM>. Fourth inner surface <NUM> is supported by second substrate <NUM>. Second <NUM> and third inner surfaces <NUM> are supported by inner substrate <NUM>.

<FIG> illustrates that the present invention may be used in relation to ophthalmic lenses comprising so-called meniscus lenses. Those skilled in the art will realise that other optical configurations are possible. For example, <FIG> shows a schematic cross section through an ophthalmic lens <NUM> comprising a liquid crystal cell flexible liquid crystal cell <NUM> that has a cell gap thickness G between a first inner surface <NUM> and a second inner surface <NUM> with liquid crystal therebetween. The liquid crystal cell <NUM> comprises a perimeter support configuration <NUM> to maintain a perimeter gap thickness PG at a perimeter of the liquid crystal cell. The support configuration <NUM> comprises a ring of <NUM> micron thick spacer sheet, and providing a perimeter gap thickness PG of approx. <NUM> microns. The liquid crystal cell <NUM> comprises a first, inner, annular support member <NUM> and a second, outer, support member <NUM>. The shape of first inner surface <NUM> is defined by a Fresnel structure (a series of annular features that provide crests and troughs). Each support member <NUM>, <NUM> is arranged to maintain the cell gap thickness G by providing support at a support location within the cell. The cell gap thickness G is not the same across the liquid crystal cell due to the presence of the Fresnel structure. In this case, the height of the support member <NUM> is smaller than that of support member <NUM>. The support locations form one or more rings concentric with a centre of the liquid crystal cell <NUM>. Liquid crystal <NUM> is provided between the first <NUM> and second <NUM> inner surfaces. Those skilled in the art will realise that other optical configurations, such as gradient-indexed lenses (GRIN) lenses may be achieved using the present invention.

The examples above demonstrate that the liquid crystal cell may comprise two concentric rings of support locations to maintain a cell gap thickness. Those skilled in the art will realise that other arrangement are possible, for example, with one (and only one) ring of support locations, or with more than two rings of support locations.

The examples above demonstrate that the rings are substantially annular. Those skilled in the art will realise that the ring need not be annular.

The examples above demonstrate lenses with particular alignments of liquid crystal. Those skilled in the art will realise that other alignments or arrangements of liquid crystal may be used, depending on the optical effect that is required.

The examples above describe contact lenses. Those skilled in the art will realise that other ophthalmic lenses may be used.

Claim 1:
An electrically-switchable flexible ophthalmic lens (<NUM>, <NUM>, <NUM>) for conforming to the eye of a user, the lens comprising:
a liquid crystal cell (<NUM>, <NUM>, <NUM>, <NUM>) for changing at least one optical characteristic of the ophthalmic lens, and having a cell gap thickness (G, G") between a first inner surface (<NUM>, <NUM>, <NUM>) and a second inner surface (<NUM>, <NUM>, <NUM>) with liquid crystal (<NUM>, <NUM>, <NUM>, <NUM>) therebetween, the flexible liquid crystal cell having a chord radius, w, and comprising:
a plurality of support members, wherein each support member is arranged to maintain the cell gap thickness by providing support at one or more support locations within the cell,
characterised in that
the support members (<NUM>, <NUM>, 107a, 107b, 207a, 207b, 307a, 307b, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) are arranged such that the support locations form two rings (<NUM>, <NUM>, <NUM>) concentric with a centre of the liquid crystal cell, the first ring located a chord measurement of <NUM>-<NUM>.34w from the centre of the liquid crystal cell and the second ring located a chord measurement of <NUM>-<NUM>.70w from the centre of the liquid crystal cell; and
the support locations form two, and only two, rings.