Patent Description:
The refractive-diffractive switchable lens or diffractive switchable lens of the present invention can be applied outside or within ophthalmic application. In latter case the lens can be called diffractive switchable ophthalmic lens. Ophthalmic lens in the present invention is defined as a diffractive switchable lens suitable for placement outside the eye such as spectacle lens or contact lenses or inside the eye such as aphakic and phakic intraocular lenses or implants placed in posterior or anterior eye chamber and also included are artificial corneas and corneal implants or inlay. For detailed explanation of the lens of the present invention, the ophthalmic application for presbyopia correction is used as a preferred embodiment.

A fixed single power lens provides good quality vision but only within a small range of viewing distances that is usually significantly narrower than the range required from near to far vision. The resulted vision deficiency is called presbyopia. There is a significant effort to develop a lens for presbyopia correction in a form of multifocal refractive or diffractive type lenses that provide multiple foci and also in a form of accommodating lenses that may change their optical surface shapes or positions inside the eye for ocular power increase for near vision. Diffractive switchable optical element according to the present invention is a lens that consequently changes the image positions between distance and near foci or fields by directing light to refractive focus and a different focus position corresponding to a diffraction order. Usually but not necessary the power corresponding to diffraction order is higher the refractive power and this difference is called Add power as a traditional reference to a power difference between near and far foci in presbyopia correction. A refractive-diffractive switchable ophthalmic lens implanted inside the eye is also called diffractive accommodating lens as switching between far and near foci occurs under the action of ciliary muscle. It is important to note that diffractive switchable lens according to the present invention has application outside ophthalmic one in so called engineering optic (microscopes, telescopes, photo-objectives, etc.).

Portney' <CIT>, "Switchable Diffractive Accommodating Lens" explained accommodation, ciliary muscle action during accommodation and prior art involving in Presbyopia correction. The same application also disclosed Sensor Cell that functioned for (a) sensing a need to focus for far or near and/or (b) actuation of an implantable accommodating lens (phakic, aphakic, corneal inlay) to focus at far or near by a direct interaction with ciliary muscle at the location of the ciliary spur. Equivalent Sensor Cell can also be used with a diffractive accommodating lens of the present invention.

The advantage of the diffractive switchable optic in switching between far and near foci over a refractive optic was described in Portney' <CIT>, "Switchable Diffractive Accommodating Lens" and also by a large group of researches:<NPL>, in the application to the spectacle lens. The operation of the described by Li G, et al spectacle lens was based on electrical control of the refractive index of thin layer of pneumatic liquid crystal by creating volume diffractive element through refractive index modulation. Though the approach is feasible, it is complicated and expensive to execute and it also requires electric field for its operation which is a challenge for ocular implant or contact lens application. Haddock at el. in <CIT> introduced further improvement to the above volume diffractive lens manufacturability. The spectacle lenses according to the above design were released by PixelOptics under EmPower name. Similar technology is under development for accommodating IOL by ELENZA, Inc.

A diffractive switchable lens according to the present invention incorporates a switchable cell and optical surfaces. A switchable cell of the present invention is an opto-mechanical device that utilizes mechanical optical switching between far and near foci by changing the optical surface shape between refractive continuous form for one focal position and diffractive form of a periodic structure for a different focal position. Refractive surface focusing ability depends on surface curvatures and diffraction surface focusing ability depends on a diffraction surface periodic structure. An optical surface can be part of a switchable cell or part of a separate optical element that together form diffractive switchable lens. Switchable cell is the center of the present invention for operation of a diffractive switchable lens.

Diffractive optic has been described by a huge volume of papers. For instance, <NPL>, described diffractive optic of blazed shape, so called surface relief shape of different diffraction orders. This type of diffractive optic is called Kinoform that allows <NUM>% of light to be directed to a single focal position formed by a single diffraction order or multiorder per Faklis and Morris explanation. Diffraction zones forming diffraction surface periodic structure can be of different profiles, rectangular, sine-wave for instance, as well as blazed surface of different profiles (parabolic, linear, sine) of a single order or multiorder composition and any one or a combination of them can be applied to a diffractive switchable lens of the present invention for so called diffraction guiding surface introduced below.

The advantage in using diffractive element is that the focal length of selected diffraction order is defined only by the periodic structure of the diffraction surface which can be built into the diffraction surface design. By the law of formation of a diffraction order, light can only be channeled along discrete diffraction orders of the diffractive lens where light constructive interference can take place thus providing predetermined separation between refractive and diffractive foci or Add power in ophthalmic application. Thus, a difference between refractive and diffractive focal positions of the diffractive accommodating lens of the present invention is predetermined by the switchable cell design itself and not by an external factor as in all refractive accommodating lens designs which makes them inherently unpredictable.

An image is physically formed at a given focus of a diffraction order if a significant percent of total light is actually channeled along the given diffraction order. This depends on the light phase shift introduced by each diffraction zone, i.e. diffraction groove height or periodic surface modulation amplitude. There are a large number of papers explanting a diffractive lens light distribution and <NPL>, offers an explanation in terms of multifocal optics and for blazed diffraction surfaces.

In a simple paraxial form the circular diffraction zones, also called grooves, echelettes or surface-relief profile, can be expressed by the formula: <MAT> where grooves radii (rj) create spherical wavefront of focal length (Fm) for a given diffraction order (m) and design wavelength (λdesign).

In case of surface relief profile and in paraxial approximation, the blaze material thickness (Hm) to produce <NUM>% efficiency at the focus of m-order diffraction is <MAT> where n = refractive index of the lens material and n' = refractive index of the medium adjacent to the diffraction surface.

In case of small spherical aberration, the periodic structure, i.e. diffraction groove periods of the diffractive optic is quite accurately defined by the Eq. <NUM> for a given focal distance. In case of a significant spherical aberration of a diffractive lens introduced to extend a range of foci around a focus of a selected diffraction order, the calculation of the groove shapes can be conducted numerically equivalent to the method described by Portney in the <CIT> for multifocal diffractive lens.

Portney' <CIT>, "Switchable Diffractive Accommodating Lens" disclosed diffractive optic with specific adjustment of its periods to create positive spherical aberration which is the most effective for depth of focus increase at a diffraction order. The same form of the diffraction surface periodicity can also be applied to the guiding surface of the diffractive switchable lens of the present invention to expand a range of foci at its diffractive focus.

The present invention relates to a pair of spectacles as defined in claim <NUM>.

A switchable cell in accordance with the present invention consists of at least three elements:.

A switchable cell may also consists of five elements: (<NUM>) elastic film, (<NUM>) optical substrate with diffraction surface, (<NUM>) transparent chamber between the elastic film and optical substrate diffraction surface filled with matching fluid, (<NUM>) optical membrane situated next to the elastic film at the opposite side from the optical substrate and (<NUM>) chamber between the elastic film and optical membrane filled with optical fluid of the refractive index that is differ from the refractive index of the optical substrate at the wavelengths of the switchable cell operation, this is so called "non-matching fluid". The corresponding chamber is called "active chamber". A switchable cell consisting of five elements listed above is called "<NUM>-element switchable cell". Thus, <NUM>-element switchable cell comprises of <NUM>-element switchable cell plus optical membrane forming active chamber with elastic film filled with non-matching fluid. The medium exterior to the film at the opposite side from the transparent chamber can be aqueous humour, air, stroma, tear layer, etc., depending on the application of the diffractive switchable lens of the present invention. The exterior medium is either ambient medium in case of <NUM>-element switchable cell or a medium of the active chamber in case of <NUM>-element switchable cell.

The optical substrate or optical membrane each may include flat or curved optical surface either at front or back surface or both surfaces. In a general form, diffractive switchable lens of the present invention consists of front and back optical surfaces and switchable cell situated between them. The diffraction surface of the optical substrate that faces the elastic film is called "guiding surface". Surface relief or blazed shape of the guiding surface is preferable embodiment because it provides highest diffractive efficiency, i.e. largest percent of light concentration in a single diffractive focus. The corresponding surface type will be used in explaining a diffraction switchable optical element of the present invention.

The operation of a switchable cell relies on the ability of matching fluid to optically mask the guiding surface resulting in optical interaction with light by the matching fluid surface shaped by the film instead of an interaction with the guiding surface. Depending how the film shapes the matching fluid, different optical characteristics can be created: (a) refractive surface shape to create refractive state with its refractive focus or, (b) diffraction surface shape with periodic structure to create diffractive state with its diffractive focus. The film itself does not contribute to a focusing ability of switchable cell because of being largely of uniform thickness and, as result, its front and back surfaces are parallel to each other, i.e. they manifest equivalement curvatures / power profiles within the thickness contribution. The external surface of the film facing the external medium is called "formable surface". Because a shape of the matching fluid formed by the film and the formable surface shape are equivalement, the formable surface is used in describing refractive or diffractive state of a switchable cell instead of referencing to a matching fluid surface shaped by the film. Thus, a focusing ability of a switchable cell is defined by the formable surface shape and a difference in refractive indices between non-matching fluid and the optical substrate (substrate).

Refractive formable surface is formed if no pressure difference exists between active and transparent chambers. This is so called relaxed state of a switchable cell as no external actuation is required in the relaxed state. In this condition the formable surface takes largely a shape of a minimum strain or, more specifically, the based surface of the diffraction guiding surface if the film is in contact with the guiding surface. Diffractive formable surface is formed if a pressure in transparent chamber is below a pressure in active chamber or medium exterior to the film and the film largely takes the shape of the guiding surface due to its elasticity. It takes place at some pressure difference called threshold level. This is so called active state of the switchable cell as a pressure difference requires an external actuation. In case of a diffraction guiding surface being a surface relief, i.e. a Kinoform, the formable surface also takes the same Kinoform surface shape to focus light at the focus position defined by the diffraction guiding surface. This is the reason to apply term "guiding" to the diffraction surface of the optical substrate as it "guides" the film shape in the active state.

The film itself is either free-standing or bonded to the guiding surface at the ridges of the diffractive grooves and its shape and, therefore, the shape of the formable surface is defined by the base surface of the diffractive guiding surface in the relaxed state. Formable refractive surface in relaxed state can be flat, curved and aspherized, i.e. of any possible shape of a base surface of the diffraction guiding surface.

There is advantage to allocate relaxed state of a switchable cell in ophthalmic application to provide far focus because of a safety consideration as far focus is desirable fall back state if an actuation of the active state fails. Therefore, the active state is to provide diffractive focus for near focus. In addition, an image formed at the diffractive focus is commonly acceptable for near vision as demonstrated by extensive clinical experience with diffractive multifocal IOLs. In general, it can be in reverse, i.e. far focus or longer focal length is formed by the diffractive focus in active state and near focus or shorter focal length by the refractive focus in relaxed state. In general, switchable states may include at least two active states in addition to refractive state or instead of refractive state with each of these active states providing its own focus position and the switching takes place between two diffractive foci.

The central advantage of a switchable cell according to the present invention is that the refractive focus of the relaxed state coincides with zero order diffractive focus formed by the formable surface Kinoform in the active state producing an image at a non-zero diffractive focus. A separation between the corresponding non-zero diffractive focus and zero order diffractive focus is only controlled by the built-in periodicity of the guiding surface which is responsible for the periodicity of the formable surface in the active state. Therefore, a separation between refractive focus in the relaxed state and diffractive focus in the active state is also controlled only the periodicity of the guiding surface.

The present invention references to a "near focus" provided by an active state of a switchable cell in an ophthalmic application but it can be an intermediate focus or even multi-foci combination if guiding surface is of a multi-zonal structure with each zone providing its own diffractive focus. In general, a reference to a "near focus" used in the present invention is a focus that differs from far focus, i.e. "near focus" may technically reference to near or intermediate focus in terms its correspondence to near or intermediate vision.

A pressure difference between active and transparent chambers of a switchable cell of the present invention is created either by increasing pressure externally to the formable surface and/or reducing pressure in the transparent chamber by an actuation mechanism. Two actuation principles can be used for switching between relaxed and active states:.

In either system, the matching fluid is pulled out from the transparent chamber through a mean of connecting the transparent chamber with the exterior of the switchable cell. This can be in a form of a channel in the substrate of the switchable cell which connects the transparent chamber within all diffractive grooves of the guiding surface to the exterior of the switchable cell.

The performance of a diffractive switchable lens in ophthalmic application (ocular implant, corneal inlay, contact lens and spectacles that are designed for presbyopia correction) relies on two functions:.

Actuation in case of a spectacle lens does not present an issue as it can be accomplished either manually or electrically by using, for instance, a solenoid but sensing for far or near need for automatic actuation the switching between far and near foci is a great challenge not only for the diffractive switchable spectacles of the present invention but for all switchable types of spectacles, electro-optical type as EmPower, for instance, and it is also a subject of the present invention.

Sensing and actuation of diffractive accommodating ocular implant can be accomplished with Sensor cell where external chamber of the Sensor cell is connected to the transparent chamber of the diffractive accommodating implant of the present invention or both external chamber is connected to transparent chamber and internal chamber of the Sensor cell to the active chamber of the switchable cell of the diffractive accommodating implant of the present invention. There is a great challenge of sensing and /or actuation of a diffractive accommodating lens without a help of Sensor cell by using internal sensing and actuation. Sensing for far or near need by a wearer of any switchable IOL or switchable contact lens is a great challenge for presbyopia correction, for instance, by electro-optical ELANZA implant. The system structurally equivalent to one used for sensing the need for far or near focus and actuation of the switching to the desired focus utilized by the diffractive switchable lens of the present invention can also be used for sensing function and triggering to the corresponding far or near focus in any switchable type of ocular implant or contact lens and it is also a subject of the present invention.

The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings, in which:.

<FIG> shows a simplest form of switchable cell as a circular disc of D ≈ <NUM>-<NUM> diameter and rectangular cross-section of W ≈ <NUM>-<NUM> thickness in ophthalmic applications. The optical axis <NUM> and segment <NUM> of the switchable cell are shown. The dimensions of a switchable cell might vary significantly in an engineering optic application.

<FIG> demonstrates a segment <NUM> of the cross-section of a preferred embodiment of an switchable cell in relaxed state. The switchable cell of this embodiment includes transparent chamber <NUM> filled with matching fluid and active chamber <NUM> filled with non-matching fluid, separated by the film <NUM>. The active chamber <NUM> is situated between film <NUM> and membrane <NUM>. The film <NUM> is free-standing or bonded to the diffractive blazed guiding surface <NUM> of the optical substrate <NUM>. Guiding surface <NUM> is shown as blazed diffraction surface of period L as one of the periods within the segment <NUM>. Diffraction surface periods vary, generally following Eq. <NUM> with an additional variation to introduce spherical aberration for depth of focus increase in the active state. Film can be made of different elastics, for instance with polydimethylsiloxane also known as PDMS. The PDMS is a Si based organic polymer that has found wide applications in MEMS and microfluidic device fabrication, soft lithography, contact lens manufacturing and device encapsulation. The PDMS material is easily available as SYLGARD <NUM> Silicone Elastomer Kit from Dow Corning, with mixing in a <NUM> : <NUM> weight ratio. It is inexpensive and fabrication processes for thin film with PDMS include spin-casting, soft lithography (molding).

The optical substrate <NUM> can be made of any appropriate optical material used in a target application which maintains guiding surface shape with the film compression in the active state, not too soft material. For instance, in IOL application, it can be silicone material (refractive index <NUM> and higher) or hydrophobic acrylic (refractive index <NUM> to <NUM>) or even PMMA. Optical fluids of wide range of refractive indices to serve as matching fluid are available. For instance, Laser Liquid from Cargille Laboratories offers optical fluids between <NUM> - <NUM> refractive indices that are colorless, stable, biocompatible and inert.

The surface facing the active chamber <NUM> is formable surface <NUM> which is used to demonstrate optical switching between refractive form of the switchable cell in the relaxed state and diffractive form in the active state.

<FIG> demonstrates the same section <NUM>' of the cross-section of the switchable cell, shown in <FIG>, but in the active state. The film <NUM>' between the transparent chamber <NUM>' and active chamber <NUM>' largely takes the shape of the blazed guiding surface <NUM> thus reshaping the transparent chamber <NUM>'. The formable surface <NUM>' takes period L at the location of the segment <NUM>' and groove height H of the guiding surface <NUM> to become blazed diffraction surface of the same periodicity and height as the guiding surface <NUM>. The elastic film <NUM>' must maintain continuity and, as a result, it has a deviation from the guiding surface in the areas <NUM> close to the step transitions <NUM> between the diffractive grooves, so called smoothing area. The smoothing area depends on a difference in pressure between the active and transparent chambers and reduces as the difference increases.

The channel <NUM> is shown to penetrate the deepest portions of the grooves of the guiding surface <NUM> to allow the matching fluid to escape from the transparent chamber <NUM>' as shown by arrow F, during switchable cell transition to the active state or to fill the transparent chamber during its transition back for the relaxed state. In a simpler form, the channel can be made in a form of a Trench channel, i.e. a channel cut across the cross-sections of the grooves. Optical effect of the Trench channel in active state is likely negligible with narrow enough channel, say <NUM> microns or less. A trench channel can be made during diffraction guiding grooves fabrication thus lowering cost of the production and desirably but not necessarily, made in a radial orientation to minimize a tearing of the film in transitions between relaxed and active states when the film strain changes. It also desirable to round trench channel edges for the same purpose.

Finite Element Analysis (FEA) was conducted to investigate a conformance of the switchable cell film to the guiding surface with a difference in pressure between the chambers. Technically, Conformance is defined as L'/L where L is a selected period of the guiding surface and L' is the width of the film conforming to the shape the guiding surface at the period L. A non-conformed width S of a given groove L is S = L - L' and is smoothing area or S-dimension.

It has appeared that Conformance is proportional to the guiding surface period L and it reduces with the reduction the period L for the same pressure difference between the active and transparent chambers. Therefore, the FEA was conducted for the smallest period of a selected aperture of the switchable cell.

A common aperture in ophthalmic application is <NUM>. This is suitable for any ocular implant and contact lens as the pupil at Near focus is commonly within <NUM> diameter. The smallest period Lmin was calculated as following:
Focal length F = <NUM> (<NUM> D of Add power); Design wavelength λdesign = <NUM>. Assuming 1st order diffraction is used for the guiding surface. Guiding surface diffractive groove radii are defined by Eq. <NUM> and groove height of the same order by the Eq. <NUM>. PDMS substrate was selected to analyze the mechanics of the large groove height H, i.e. at fairly low refractive index n = <NUM> (PDMS material) against tear layer or aqueous humour of refractive index n' = <NUM>. Matching fluid is also has n=<NUM> refractive index. This leads to the minimum period Lmin = <NUM> and groove height H-<NUM> = <NUM>.

A selection of <NUM> aperture would lead to Lmin = <NUM> microns minimum period for the same material and optical parameters selection.

Film thickness of <NUM> microns was selected to be comparable with the groove height and for its manufacturability. The film can be "free standing" over the guiding surface or "bonded to ridges" of the guiding blazed diffraction surface, for instance, by oxygen plasma process. "Free standing" setup which does not require additional bonding fabrication step was used and a rounding was added to each ridge peak to prevent tearing of the film with the film potentially sliding over the ridges with film strain changes during transitions between active and relaxed states.

The corresponding Conformance curve is shown in the graph below:
<IMG>.

The graph demonstrates a typical Conformance curve shape for different film thicknesses, groove widths and heights - the curve rapidly increases with a pressure difference between the chambers initially and then it is slowing down with approachment to a full conformance to the guiding surface. Each groove of an switchable cell has its own Conformance curve with Conformance curve shifts to the left (lower pressure difference of the horizontal axis) with a groove period increase. Variable film thickness (thicker along a larger period of the guiding surface and thinner along a smaller period) might be beneficial for Conformance consistency for different periods.

General fitting function of a Conformance Curve is: <MAT> where y = Conformance and x = pressure difference in PSI units.

In case of the example A above for Lmin = <NUM> and H = <NUM>, the parameters of the Conformance Curve shown in graph above are: a = -<NUM>; b = <NUM>; c = <NUM>; d = <NUM>.

Use of materials with different refractive indices for the optical substrate with the same periodic structure of the guiding surface does not impact diffractive focal length and only impacts the groove height H per the Eq. <NUM>. The periodicity is the most important parameter and the outcome of FEA are valid for different substrate materials. The only effect of the groove height reduction is a force threshold reduction for a transition between relaxed and active states of the switchable cell.

A radial strain of the film in relaxed state can be added to the film to facilitate its return to the original shape in the relaxed state. Film stretching in a direction parallel the base surface of the diffraction guiding surface in case of the film contact with the guiding surface. In case of a radial strain, the Conformance curve shifts to the right, i.e. to higher pressure difference in the horizontal axis. A radial strain of the film can be used to control a force threshold of the transition between relaxed and active states of the switchable cell.

The blazed guiding surface may also include its own "smoothing" at the transitions between the grooves, i.e. instead of having close to the theoretical step transition from one groove to another, the transitions are smoothed out. A guiding surface smoothing would allow (a) to use larger tool radius for the guiding surface manufacturing instead of more expensive and easily damaged single-point diamond tool, and (b) to increase cutting feed-rate of the fabrication of the corresponding surface or mold insert also to reduce the fabrication cost.

The question is on a Diffraction Efficiency (DE) of the switchable cell in active state. The DE geometrical definition was used to calculate DE of the ideal (theoretical) Kinoform with the smoothing defined by S-dimension: Diffraction Efficiency equals the sum of all area of the grooves coinciding with the blazed surface of the theoretical Kinoform to the area of the theoretical Kinoform for selected aperture.

A DE reduces with the increase of fraction of the smoothing area width to the groove period. It has appeared that a linear regression function per smoothing width (S-dimension) defines the Diffraction Efficiency for a given aperture of the switchable cell. For instance, for <NUM> aperture used in the Example A above, the DE is determined by: <MAT> where DE = Diffraction Efficiency, S is smoothing dimension in microns.

For instance, for <NUM> aperture and pressure difference to achieve conformance of about <NUM> at the minimum period Lmin = <NUM>, the Diffraction Efficiency of the switchable cell is following:
S ≈ <NUM> = <NUM>, say with a rounding of the groove ridges, S = <NUM>, i.e. ≈<NUM>% of the minimum period of <NUM> is allocated to film "smoothing". Per Eq. <NUM>, the DE = <NUM> which is fairly high even in using such conservative assessment of the film conformance.

<FIG> illustrates front view of switchable cell <NUM> with optical axis <NUM>' of diffractive accommodating aphakic IOL <NUM> with internal actuation. The switchable cell <NUM> is joint with two actuation members <NUM>, <NUM> that incorporate actuation chambers <NUM>, <NUM> correspondently. An actuation chamber is formed by an elastic membrane to enable it to change its volume if the actuation member is stretched out.

<FIG> shows front view of the anterior member <NUM> of the diffractive accommodating aphakic IOL <NUM> with internal actuation. The anterior member <NUM> is shaped by the anterior optical surface of the diffractive accommodating lens <NUM> and largely flat surface posteriorly. The <FIG> also shows a cut out <NUM> on the back of the anterior member for placement the switchable cell <NUM> joined by the cut outs <NUM>, <NUM>' for placement the actuation members <NUM>, <NUM>.

<FIG> illustrates front view of the posterior member <NUM> of the diffractive accommodating aphakic IOL <NUM> with internal actuation. The posterior member <NUM> includes haptics <NUM>, <NUM> attached to the posterior member optic body <NUM> for fixation the diffractive accommodating aphakic IOL <NUM> inside the capsular bag of the eye. The posterior member optic body <NUM> is shaped by the posterior optical surface of the diffractive accommodating lens <NUM> and largely flat surface anteriorly. There are also actuation wings <NUM>, <NUM> attached to the posterior member optic body <NUM> to serve for bonding the posterior member <NUM> to the corresponding actuation members <NUM>, <NUM>.

<FIG> demonstrates side view of aphakic diffractive accommodating lens <NUM> assembled with the anterior and posterior members <NUM>, <NUM> and the switchable cell <NUM>. The anterior and posterior members <NUM>, <NUM> are separated by the width of the actuation members <NUM>, <NUM>. The optic diameter of the anterior member <NUM> is shown to be larger the diameter of optic body <NUM> of the posterior member <NUM> in order for the haptics <NUM>, <NUM> that are coming out from the optic body <NUM> to be in contact with the anterior member <NUM> at its periphery. It is also shown a slight cut out <NUM> at the periphery of the anterior member <NUM> where the angulated haptic <NUM> rests. The identical cut out is located at the opposite side of the anterior member <NUM> for resting of the other haptic <NUM>. The aphakic diffractive accommodating lens <NUM> is shown in two states: relaxed state by the position of haptics <NUM>, <NUM> and active state by the position of haptics <NUM>', <NUM>'. Front surfaces of the actuation members <NUM>, <NUM> are bonded to the posterior of the anterior member <NUM> and posterior surfaces of the actuation members <NUM>, <NUM> are bounded to the actuation wings <NUM>, <NUM> of the posterior member <NUM>. A volume of the actuation chambers <NUM>, <NUM> expends with the increase in the separation <NUM> between the anterior members <NUM> and posterior member <NUM>. The separation <NUM> increases with the haptics compression and corresponding angulation change from <NUM>, <NUM> position to <NUM>', <NUM>' position which results in the haptics attached to the optic <NUM> of the posterior member <NUM> pushing the anterior member <NUM> apart from the posterior member <NUM> by a magnitude ΔI. This shift is shown by a new position of the anterior member <NUM>'. Separation <NUM> increase enlarges volumes of the actuation chambers <NUM>, <NUM> which pulls out the matching fluid from the transparent chamber of the switchable cell <NUM>. This, in turn, switches the formable surface <NUM> from the refractive state for far focus into formable surface <NUM> of the diffractive state for near focus.

<FIG> demonstrate cross-section views of the switchable cell <NUM> with actuation members <NUM>, <NUM> in relaxed state and the switchable cell <NUM>' with actuation members <NUM>', <NUM>' in active state. The width of the actuation members <NUM>, <NUM> along the optical axis <NUM>' in the relaxed state is shown to be narrower the width of the actuation members <NUM>', <NUM>' in active state. This is to demonstrate that the corresponding actuation chambers <NUM>, <NUM> in relaxed state is enlarged into actuation chambers <NUM>', <NUM>' in the active state. In turn, it transforms the refractive formidable surface <NUM> of the switchable cell <NUM> into diffraction surface <NUM> of the switchable cell <NUM>'. The formable surface is in contact with aqueous humour in the eye.

<FIG> demonstrates front view of the diffractive switchable contact lens <NUM>. The contact lens <NUM> includes balance <NUM> at the bottom of the lens to maintain the lens meridional orientation. The contact lens <NUM> also includes the actuation ledge <NUM> at the bottom of the lens to facilitate interaction with the lower eyelid when viewing down for near focus similar to a performance of an alternating contact lenses. The contact lens <NUM> includes a switchable cell <NUM> within the optic zone <NUM> which joints the actuation chamber <NUM>.

<FIG> demonstrate cross-section views of the diffractive switchable contact lens <NUM> in relaxed state <NUM>, and active state <NUM> correspondently. The switchable cell <NUM> is located at the lower part of the lens <NUM> and consists of optical substrate <NUM> with its back surface forming a part of the back surface or base of the contact lens <NUM>. The optical substrate <NUM> can be made of the same material as the contact lens <NUM> or a different material bonded to the lens depending if the transparent chamber impermeability can be maintained. The guiding surface <NUM> of the substrate <NUM> is facing inside the lens with the film <NUM> free-standing on or bonded to the ridges of the convex shape of the guiding surface <NUM> in the relaxed state. There is a transparent chamber filled with the matching fluid between the film <NUM> and guiding surface <NUM>. The formable surface of the film <NUM> is facing a narrow chamber filled with tear medium when the lens <NUM> is fitting on the eye. This chamber acts as the active chamber of the switchable cell <NUM>. The actuation chamber <NUM> is connected to the transparent chamber of the switchable cell <NUM> for the matching fluid transfer between them to switch between relaxed and active states. The actuation chamber <NUM> is bonded to the actuation level <NUM> located inside or adjacent to the actuation ledge <NUM> shown in relaxed state. As the actuation ledge <NUM> is bent by the lower eyelid pressure when the contact lens wearer looks down for near focus, the actuation level <NUM> turns. The actuation level turn expands the actuation chamber <NUM> in the relaxed state into actuation chamber <NUM>' in the active state by pulling out the matching fluid from the transparent chamber of the switchable cell <NUM>. As the result, the film <NUM>' takes the shape of the guiding surface <NUM> thus modifying the formable surface into a diffraction surface for near focus. The transition between the relaxed and active states corresponds to a shift by ΔC distance between unturned actuation level <NUM> and turned actuation level <NUM>'.

<FIG> depict right half <NUM> of switchable spectacles to demonstrate a sensing a need for far or near focus. The <FIG> shows front view of right half of the spectacles. It consists of frame <NUM> and switchable spectacle lens <NUM>. The IR emitter <NUM> is installed at one side of the switchable spectacle lens <NUM>. An IR sensor <NUM> is installed on the opposite side of the switchable spectacle lens <NUM>, actually two sensors <NUM>, <NUM> to provide better sensitivity for sensing. Each IR sensor <NUM> or <NUM> and IR emitter <NUM> lie in approximately horizontal planes <NUM> and <NUM> correspondently. The depiction of the eye in the <FIG> demonstrates the eye's straight forward gaze for far focus through the switchable spectacle lens <NUM> with the upper eyelid <NUM> being in its upper position. <FIG> is upper view of the spectacles half <NUM> shown on the <FIG>: the IR emission from the IR emitter <NUM> shown by arrows is reflected off the front surface <NUM> of the eye ball as shown by solid line <NUM> and reaches the IR sensor <NUM> on the opposite side of the frame. <FIG> demonstrates front view of the same switchable spectacles half <NUM> in the condition when the wearer looks down for near focus with the upper eyelid <NUM>' in its lower position. The <FIG> shows the upper view of the <FIG>: IR emission from the IR emitter <NUM> is fully or partially obstructed by the upper eyelid <NUM>' thus changing the amount of IR radiance received by the IR sensor <NUM> or both sensors <NUM>, <NUM>. The intended reflection from the front surface <NUM> of the eye ball is shown by the broken line <NUM>'. The outcome of the radiation obstruction is a lower electrical signal from the IR sensor which triggers an actuation of the switchable cell from relaxed state for far focus into active state for near focus. The <FIG> showed the switchable cell <NUM> located at a lower part of the switchable spectacle lens <NUM>.

<FIG> illustrates the use of switchable cell for low vision application to provide magnification for a visually impaired person. It depicts a spectacle like structure <NUM> with two pairs of diffractive switchable cells OF+EF for straight forward far vision (subscript F) and ON+EN for down near vision (subscript N). A front diffractive switchable cell OF or ON serves as the objective of the Galilean telescope and back diffractive switchable cell EF or EN serves as the eyepiece of the corresponding Galilean telescope. High order diffraction can be used to reduce focal lengths in both objective and eyepiece of each pair to shorten the Galilean telescope for its placement onto the spectacle like structure <NUM>.

<FIG> demonstrates Longitudinal Spherical Aberration (LSA) at Far focus by the Diffractive Switchable Ophthalmic Lens (Diffractive Accommodating Lens) in the switching cell relaxed state according to the specifications listed in Tables <NUM> and <NUM>.

The LSA for Far focus demonstrates positive spherical aberration for up to about <NUM> from the lens center and negative spherical aberration outside <NUM> distance which is the characteristic of bi-sign asphericity.

<FIG> demonstrates Longitudinal Spherical Aberrations at Near focus by the Diffractive Accommodating Lenses produced at (-<NUM>)-order diffraction with switchable cell being in the active state per specifications of Eye model and Diffractive Accommodating Lens in Tables <NUM> and <NUM>. The switchable cell is limited to <NUM> diameter of optical aperture in this example.

The LSA at Near focus shown on <FIG> manifests significant positive spherical aberration at (-<NUM>)-order diffraction to create retinal image from a near object placed not only around <NUM> viewing distance (<NUM> D) but through about <NUM> of near viewing distance, i.e. to offer the increased depth of focus at near of about <NUM> D. The increase in depth of focus at near is demonstrated by the corresponding LSA shape which starts at shorter near focus position at the lens center and gradually shifts further away to create a negative slope of the power graph which is most effective for a depth of focus increase.

Specification of the guiding surface of the switchable cell with large amount of spherical aberration to extend depth of focus at (-<NUM>)-order diffraction is provided in Table <NUM> where its periodicity (referenced to "Large LSA") is compared with the periodicity that produces spherical wavefront per Eq. <NUM> (referenced to "Small LSA").

Depth of focus or progressive foci feature at near diffraction focus in active state was increased by modifying the phase coefficients for (-<NUM>) order diffraction for spherical wavelength to include spherical aberration that spreads the light along the optical axis at the near diffraction focus either to improve near close up or improve intermediate vision capability in addition to providing near.

A surface position where the optical axis intersects an optical surface is called optical center. Each optical surface of the lens has its own optical center which line up on the optical axis in centered optical system. Diffractive grooves are defined by their radii from the optical center and diffractive grooves periodicity is defined by differences in consecutive groove radii, i.e. groove periods. Per the example of the <FIG>, there are <NUM> grooves within about <NUM> diameter with central two grooves radii the periodicity producing enhanced depth of focus being substantially smaller the corresponding radii of the same orders defined by Eq. <NUM>. Central groove means closest to the optical center. The periodicity producing the depth of focus increase also has a radius of a peripheral groove that reaches similar magnitude as the groove radius of the same order defined by the Eq. <NUM>, 11th groove per Table <NUM>, in this case. "Substantially smaller" generally means to be by about <NUM>% or more smaller and "similar" generally means to be within about ±<NUM>%. The higher order groove radii of the periodicity described exceed groove radii of the corresponding orders per Eq. <NUM>. The described comparison between any diffraction surface in terms of their groove radii that produces extended positive (geometrical) spherical aberration and diffractive surface that produced small amount of spherical wavefront, i.e. groove radii analogous to Eq. <NUM>, is only applicable for the same order of diffraction (1st or higher), by comparing the same order of groove radii, the same design wavelength and substantially similar focal lengths, say within about ±<NUM>%.

Phase coefficients to enhance depth of focus at a diffraction focus can be applied to a monofocal diffractive non-accommodating lens and multifocal diffractive optics where light is split between far and near foci and near image is formed, for example, by (-<NUM>)-order diffraction. Appropriate phase coefficients can be applied to a multifocal diffractive optic that leads to substantially smaller central (closest to the optical center) diffractive groove radii of the periodic structure for enhanced depth of focus than the central groove radii of the periodic structure that produces spherical wavefront, i.e. per Eq.<NUM>. In addition, the same periodic structure that increases depth of focus reaches a groove radius towards surface periphery that is similar to the groove radius of the same order that produces spherical wavefront, i.e. equivalent to Eq.<NUM>. In case of an annular zone with progressive foci feature at its diffraction focus, the radii of central grooves are defined as starting at the internal side of the annular zone and are also referenced to as "central grooves" or "closest to the optical center grooves".

Claim 1:
A pair of spectacles having a frame, the pair of spectacles comprising:
a switchable lens (<NUM>) attached to the pair of spectacles, the switchable lens (<NUM>) configured to switch its foci from a far focal length to a near focal length, where the near focal length is smaller than the far focal length;
an infrared emitter (<NUM>) disposed at a horizontal edge of the at least one switchable lens (<NUM>), the infrared emitter (<NUM>) configured to emit an infrared radiation;
an infrared sensor (<NUM>, <NUM>) configured to detect the infrared radiation from the infrared emitter (<NUM>);
wherein the switchable lens (<NUM>) is configured to switch to its far focal length when the infrared sensor (<NUM>, <NUM>) detects an intensity of infrared radiation that has been emitted and reflected off a front surface of a wearer's eye ball when the wearer is looking forward; and
characterized in that
the infrared sensor (<NUM>, <NUM>) is disposed at an opposite side periphery of the at least one switchable lens (<NUM>), and
in that the switchable lens (<NUM>) is configured to switch to its near focal length when the infrared sensor (<NUM>, <NUM>) detects a different intensity of infrared radiation when the infrared radiation is changed in reflecting off the front surface of the wearer's eye ball by an upper eyelid of the wearer when the wearer is looking downward.