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WO2020225449A1 - An ophthalmic progressive addition lens adapted for a wearer - Google Patents

An ophthalmic progressive addition lens adapted for a wearer Download PDF

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Publication number
WO2020225449A1
WO2020225449A1 PCT/EP2020/062956 EP2020062956W WO2020225449A1 WO 2020225449 A1 WO2020225449 A1 WO 2020225449A1 EP 2020062956 W EP2020062956 W EP 2020062956W WO 2020225449 A1 WO2020225449 A1 WO 2020225449A1
Authority
WO
WIPO (PCT)
Prior art keywords
equal
gaze directions
domain
lens
wearer
Prior art date
Application number
PCT/EP2020/062956
Other languages
French (fr)
Inventor
Sylvain Mercier
Cyril Guilloux
Mélanie HESLOUIS
Original Assignee
Essilor International
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Essilor International filed Critical Essilor International
Priority to EP20723178.8A priority Critical patent/EP3966625A1/en
Priority to JP2021559685A priority patent/JP2022532028A/en
Publication of WO2020225449A1 publication Critical patent/WO2020225449A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
    • G02C7/00—Optical parts
    • G02C7/02—Lenses; Lens systems ; Methods of designing lenses
    • G02C7/06—Lenses; Lens systems ; Methods of designing lenses bifocal; multifocal ; progressive
    • G02C7/061—Spectacle lenses with progressively varying focal power
    • G02C7/063—Shape of the progressive surface
    • G—PHYSICS
    • G02—OPTICS
    • G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
    • G02C7/00—Optical parts
    • G02C7/02—Lenses; Lens systems ; Methods of designing lenses
    • G02C7/024—Methods of designing ophthalmic lenses
    • G02C7/028—Special mathematical design techniques
    • G—PHYSICS
    • G02—OPTICS
    • G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
    • G02C7/00—Optical parts
    • G02C7/02—Lenses; Lens systems ; Methods of designing lenses
    • G02C7/06—Lenses; Lens systems ; Methods of designing lenses bifocal; multifocal ; progressive
    • G02C7/061—Spectacle lenses with progressively varying focal power
    • G02C7/063—Shape of the progressive surface
    • G02C7/065—Properties on the principal line
    • G—PHYSICS
    • G02—OPTICS
    • G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
    • G02C7/00—Optical parts
    • G02C7/02—Lenses; Lens systems ; Methods of designing lenses
    • G02C7/024—Methods of designing ophthalmic lenses
    • G02C7/027—Methods of designing ophthalmic lenses considering wearer's parameters

Definitions

  • An ophthalmic progressive addition lens adapted for a wearer
  • the invention relates to an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition.
  • the invention further relates to a method for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition.
  • the ophthalmic lenses in particular progressive additional ophthalmic lenses may comprise optical aberrations such as unwanted astigmatism resulting from the optical design of the ophthalmic lens.
  • the lens designer may modify the optical design so as to try to reduce optical aberrations such as unwanted astigmatism however in some cases such optical aberrations cannot be totally avoided. In some other cases reducing the unwanted astigmatism requires reducing the optical performance of the ophthalmic lens.
  • the optical design of the lens may be adapted to change the distribution of the optical aberrations so as to adapt the optical design to the wearer.
  • ophthalmic lenses are intended to be provided in pairs, one for the right eye and one for the left eye.
  • the optical design should be adapted to provide good binocular vision to the wearer.
  • One object of the present invention is to provide such an ophthalmic progressive addition lens.
  • the invention proposes an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, said progressive ophthalmic lens having in given wearing conditions:
  • optical power in the gaze direction corresponding to the fitting cross is greater than or equal to 5% of the prescribed addition.
  • having an optical function symmetrical with respect to the meridian line at least over the domain of gaze directions mostly used by the wearer when wearing the progressive addition lens greatly improves the binocular vision of the wearer.
  • having an optical power greater than or equal to 5% of the prescribed addition at the fitting cross allows a softer progression of the optical power along the meridian, increasing the vision comfort of the wearer.
  • MaxSymPpo max GapPpo, , with GapPpo, being defined for two gaze
  • the ophthalmic progressive addition lens is adapted for a hyperopic wearer
  • the ophthalmic progressive addition lens is adapted for an emmetropic wearer and MaxSymPpo is smaller than or equal to 0.09*Add; and/or
  • the ophthalmic progressive addition lens is adapted for a myopic wearer and MaxSymPpo is smaller than or equal to 0.09*Add; and/or
  • MaxSymAsr max GapAsr, , with GapAsr, being defined for two gaze
  • the ophthalmic progressive addition lens is adapted for a hyperopic wearer
  • the ophthalmic progressive addition lens is adapted for an emmetropic wearer and MaxSymAsr is smaller than or equal to 0.09*Add; and/or
  • the ophthalmic progressive addition lens is adapted for a myopic wearer and MaxSymAsr is smaller than or equal to 0.09*Add; and/or
  • the ophthalmic progressive addition lens is adapted for a hyperopic wearer
  • the ophthalmic progressive addition lens is adapted for an emmetropic wearer and RMSSymPpo is smaller than or equal to 0.04*Add; and/or
  • the ophthalmic progressive addition lens is adapted for a myopic wearer and RMSSymPpo is smaller than or equal to 0.04*Add; and/or
  • the ophthalmic progressive addition lens is adapted for an emmetropic wearer and RMSSymAsr is smaller than or equal to 0.04*Add; and/or
  • the ophthalmic progressive addition lens is adapted for a myopic wearer and RMSSymAsr is smaller than or equal to 0.04*Add; and/or
  • the module of unwanted astigmatism in the given wearing conditions is smaller than or equal to the prescribed addition of the wearer at least over said domain of gaze directions (a, b);
  • the difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°;
  • the given wearing conditions are standard wearing conditions
  • the given wearing conditions are customized wearing condition
  • the prescribed addition is greater than or equal to 0.50 Diopter, and smaller than or equal to 5 Diopters, for example smaller than or equal to 4 Diopters.
  • the invention also relates to a pair of ophthalmic progressive addition lenses, wherein each ophthalmic progressive addition lens is according to the invention.
  • the invention relates to a method, for example implemented by computer means, for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, comprising:
  • optical function having:
  • the optical function is determined so that the module of unwanted astigmatism in the given wearing conditions is smaller than or equal to the prescribed addition of the wearer at least over said domain of gaze directions (a, b).
  • the optical function is determined so as to further comprise a fitting cross FC (OIFC, bk ) and in the given wearing conditions having a difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°.
  • the invention also relates to a method of obtaining an ophthalmic progressive addition lens adapted for a wearer having a prescribe addition Add, the method comprising the steps of the method of determining an optical function of an ophthalmic progressive addition lens according to the invention and further comprises manufacturing an ophthalmic lens having the determined optical function.
  • the invention further relates to a computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, causes the processor to carry out the steps of the methods according to the invention.
  • the invention also relates to a computer-readable storage medium having a program recorded thereon; where the program makes the computer execute the method of the invention.
  • the invention further relates to a device comprising a processor adapted to store one or more sequence of instructions and to carry out at least one of the steps of the method according to the invention.
  • Embodiments of the present invention may include apparatuses for performing the operations herein. These apparatuses may be specially constructed for the desired purposes, or it may comprise a general purpose computer or Digital Signal Processor ("DSP") selectively activated or reconfigured by a computer program stored in the computer.
  • DSP Digital Signal Processor
  • Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs) electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
  • a computer readable storage medium such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs) electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
  • Figures 1 and 2 show, diagrammatically, optical systems of eye and lens and ray tracing from the center of rotation of the eye;
  • Figure 3 shows the field vision zones of an ophthalmic progressive addition lens
  • Figures 4 and 5 illustrate examples of optical functions of ophthalmic progressive addition lenses according to the invention.
  • Prescription data refers to one or more data obtained for the wearer and indicating for at least an eye, preferably for each eye, a prescribed sphere SPHp, and/or a prescribed astigmatism value CYLp and a prescribed axis AXISp suitable for correcting the ametropia of each eye for the wearer and a prescribed addition Add suitable for correcting the presbyopia of each of his eyes.
  • the prescribed addition is transmitted by the ECP when he/she orders the lens to a lens manufacturer.
  • the lens manufacturer prescribed addition usually inscribes information relative to the prescribed addition on the paper packaging of the delivered lens.
  • the prescribed addition may be also determined from engravings located on the lens and still visible after the lens is edged and when mounted in said spectacle frame chosen by the wearer.
  • the lens may be a standard type lens but also a lens for information glasses, wherein the lens comprises means for displaying information in front of the eye.
  • the lens may also be suitable for sunglasses or not. All ophthalmic lenses of the invention may be paired so as to form a pair of lenses (left eye LE, right eye RE).
  • a progressive ophthalmic lens“design” results of an optimization of a progressive -Si- surface so as to restore a presbyope’s ability to see clearly at all distances but also to optimally respect all physiological visual functions such as foveal vision, extra-foveal vision, binocular vision, dynamic vision and to minimize unwanted astigmatisms.
  • a progressive lens design comprises:
  • optical characteristics are part of the "designs" defined and calculated by ophthalmic lens designers and that are provided with the progressive lenses.
  • a “gaze direction” is identified by a couple of angle values (a,b), wherein said angles values are measured with regard to reference axes centered on the center of rotation of the eye, commonly named as "CRE". More precisely, figure 1 represents a perspective view of such a system illustrating parameters a and b used to define a gaze direction.
  • Figure 2 is a view in the vertical plane parallel to the antero-posterior axis of the wearer's head and passing through the center of rotation of the eye in the case when the parameter b is equal to 0.
  • the center of rotation of the eye is labeled CRE.
  • the axis CRE-F' shown on Figure 2 in a dot-dash line, is the horizontal axis passing through the center of rotation of the eye and extending in front of the wearer - that is the axis CRE-F' corresponding to the primary gaze direction.
  • the lens is placed and centered in front of the eye such that the axis CRE-F' cuts the front surface of the lens on a point called the fitting cross, which is, in general, present on lenses to enable the positioning of lenses in a frame by an optician.
  • the fitting cross is point on a lens as specified by the manufacturer to be used as a reference point for positioning the lens in front of a wearer’s eye.
  • the fitting cross is defined by the norm ISO 8980-2, Ophthalmic Optics.
  • the point of intersection of the rear surface of the lens and the axis CRE-F' is the point, O.
  • a value of radius q' of 25.5 mm corresponds to a usual value and provides satisfying results when wearing the lenses. Other value of radius q' may be chosen.
  • a given gaze direction represented by a solid line on figure 1, corresponds to a position of the eye in rotation around CRE and to a point J (see figure 2) of the vertex sphere.
  • the angle b is the angle formed between the axis CRE-F' and the projection of the straight line CRE-J on the horizontal plane comprising the axis CRE-F'; this angle appears on the scheme on Figure 1.
  • the angle a is the angle formed between the axis CRE-J and the projection of the straight line CRE-J on the horizontal plane comprising the axis CRE-F'; this angle appears on the scheme on Figures 1 and 2.
  • a given gaze view thus corresponds to a point J of the vertex sphere or to a couple (a,b).
  • the image of a point M in the object space, located at a given object distance is formed between two points S and T corresponding to minimum and maximum distances JS and JT, which would be the sagittal and tangential local focal lengths.
  • the image of a point in the object space at infinity is formed, at the point F'.
  • the distance D corresponds to the rear frontal plane of the lens.
  • a mean refractive power RRO(a,b) For each gaze direction (a,b), a mean refractive power RRO(a,b), a module of astigmatism ASR(a ⁇ ) and an axis ACE(a,b) of this astigmatism, and a module of resulting (also called residual or unwanted) astigmatism ASR(a ⁇ ) are defined.
  • Astigmatism refers to astigmatism generated by the lens, or to residual astigmatism (resulting astigmatism) which corresponds to the difference between the prescribed astigmatism (wearer astigmatism) and the lens-generated astigmatism; in each case, with regards to amplitude or both amplitude and axis.
  • an“optical function” corresponds to a function providing for each gaze direction the effect of an optical lens on the light ray passing through the optical lens.
  • the optical function may comprise dioptric function, light absorption, polarizing capability, reinforcement of contrast capacity, etc...
  • the dioptric function corresponds to the optical lens power (mean power, astigmatism etc... ) as a function of the gaze direction.
  • Ergorama is a function associating to each gaze direction the usual distance of an object point. Typically, in far vision following the primary gaze direction, the object point is at infinity. In near vision, following a gaze direction essentially corresponding to an angle a of the order of 35° and to an angle b of the order of 5° in absolute value towards the nasal side, the object distance is of the order of 30 to 50 cm.
  • US patent US A-6, 318,859 may be considered. This document describes an ergorama, its definition and its modeling method.
  • points may be at infinity or not.
  • Ergorama may be a function of the wearer's ametropia. Using these elements, it is possible to define a wearer optical power and astigmatism, in each gaze direction.
  • An object point M at an object distance given by the ergorama is considered for a gaze direction (a,b).
  • the object proximity can be considered as the inverse of the distance between the object point and the front surface of the lens, on the corresponding light ray.
  • the image of a point M having a given object proximity is formed between two points S and T which correspond respectively to minimal and maximal focal distances (which would be sagittal and tangential focal distances).
  • the quantity Proxl is called image proximity of the point M:
  • an optical power PPO as the sum of the image proximity and the object proximity.
  • the optical power is also called refractive power.
  • an astigmatism AST is defined for every gaze direction and for a given object proximity 1 1
  • This definition corresponds to the astigmatism of a ray beam created by the lens.
  • the resulting astigmatism ASR is defined for every gaze direction through the lens as the difference between the actual astigmatism value AST for this gaze direction and the prescribed astigmatism.
  • the residual astigmatism (resulting astigmatism) ASR more precisely corresponds to module of the vectorial difference between actual (AST, AXE) and prescription data (CYLp, AXISp).
  • the characterization of the lens refers to the ergorama-eye-lens system described above.
  • lens' is used in the description but it has to be understood as the 'ergorama-eye-lens system'.
  • the values in optic terms can be expressed for gaze directions. Conditions suitable to determine of the ergorama-eye-lens system are called in the frame present invention "given wearing conditions".
  • the given wearing conditions are to be understood as the position of the lens element with relation to the eye of a wearer, for example defined by a pantoscopic angle, a cornea to lens distance, a pupil-cornea distance, a center of rotation of the eye to pupil distance, a center of rotation of the eye to lens distance and a wrap angle.
  • a "far-vision gaze direction”, referred as FVGD, is defined for a lens, as the vision gaze direction corresponding to the far vision (distant) reference point and thus (CIFV, FV), where the mean refractive power is substantially equal to the mean prescribed power in far vision, the mean prescribed power being equal to SPHp+(CYFp/2).
  • far-vision is also referred to as distant-vision. In the sense of the invention far vision is to be understood as vision at a distance greater than or equal to 4 meters.
  • NVGD near-vision gaze direction
  • OINV,PNV near vision
  • near vision is to be understood as vision at a distance smaller than or equal to 50 cm.
  • substantially equal means a“equal with a tolerance lower than 15%”.
  • FCGD fitting-cross gaze direction
  • the "meridian line", referred as ML(a,P), of a progressive addition lens is a line defined from top to bottom of the lens and passing through the fitting cross where one can see clearly an object point.
  • Said meridian line is defined on the basis of the repartition of module of resulting astigmatism, ASR, over the (a, b) domain and substantially correspond to the center of the two central iso-module of resulting astigmatism values which value is equal to 0. 5 Diopter.
  • the meridian line is calculated according to following method:
  • FCGD gaze direction
  • the meridian line is defined as the curve passing through the following points:
  • Micro-markings also called “alignment reference marking” have been made mandatory on progressive lenses by the harmonized standards ISO 13666:2012 (“Alignment reference marking: permanent markings provided by the manufacturer to establish the horizontal alignment of the lens or lens blank, or to re-establish other reference points") and ISO 8980-2 ("Permanent marking: the lens has to provide at least following permanent markings: alignment reference markings comprising two markings distant from 34 mm one of each other, equidistant from a vertical plane passing through the fitting cross or the prism reference point"). Micro-markings that are defined the same way are also usually made on complex surfaces, such as on a front surface of a lens with a front surface comprising a progressive or regressive front surface.
  • Temporal markings may also be applied on at least one of the two surfaces of the lens, indicating positions of control points (reference points) on the lens, such as a control point for far- vision, a control point for near-vision, a prism reference point and a fitting cross for instance.
  • the prism reference point PRP is considered here at the midpoint of the straight segment which connects the micro-markings. If the temporary markings are absent or have been erased, it is always possible for a skilled person to position the control points on the lens by using a mounting chart and the permanent micro-markings.
  • standard ISO 10322-2 requires micro-markings to be applied. The centre of the aspherical surface of a semi-finished lens blank can therefore be determined as well as a referential as described above.
  • Figure 3 shows field vision zones of an ophthalmic progressive addition lens 30 where said lens comprises a far vision (distant vision) zone 32 located in the upper part of the lens, a near vision zone 36 located in the lower part of the lens and an intermediate zone 34 situated between the far vision zone 32 and the near vision zone 36.
  • the meridian line is referred as 38.
  • the near-vision point can be shifted horizontally with respect to a vertical line passing through the distance- vision point, when the lens is in wearing conditions.
  • This shift which is in the direction of the nasal side of the lens, is usually referred to as“inset” and its value may be expressed as the ⁇ b Nn ⁇ I ⁇
  • The“wearing conditions” are to be understood as the position of the ophthalmic lens with relation to the eye of a wearer, for example defined by a pantoscopic angle, a Cornea to lens distance, a Pupil-cornea distance, a CRE to pupil distance, a CRE to lens distance and a wrap angle.
  • the Cornea to lens distance is the distance along the visual axis of the eye in the primary position (usually taken to be the horizontal) between the cornea and the back surface of the lens ; for example equal to 12mm.
  • the Pupil-cornea distance is the distance along the visual axis of the eye between its pupil and cornea ; usually equal to 2mm.
  • the CRE to pupil distance is the distance along the visual axis of the eye between its center of rotation (CRE) and cornea ; for example equal to 11.5mm.
  • the CRE to lens distance is the distance along the visual axis of the eye in the primary position (usually taken to be the horizontal) between the CRE of the eye and the back surface of the lens, for example equal to 25.5mm.
  • the Pantoscopic angle is the angle in the vertical plane, at the intersection between the back surface of the lens and the visual axis of the eye in the primary position (usually taken to be the horizontal), between the normal to the back surface of the lens and the visual axis of the eye in the primary position ; for example equal to 8
  • the wrap angle is the angle in the horizontal plane, at the intersection between the back surface of the lens and the visual axis of the eye in the primary position (usually taken to be the horizontal), between the normal to the back surface of the lens and the visual axis of the eye in the primary position for example equal to 0°.
  • An example of standard wearer condition may be defined by a pantoscopic angle of -8°, a Cornea to lens distance of 12 mm, a Pupil-cornea distance of 2 mm, a CRE to pupil distance of 11.5 mm, a CRE to lens distance of 25.5 mm and a wrap angle of 0°.
  • Wearing conditions may be calculated from a ray-tracing program, for a given lens.
  • the invention relates to an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add.
  • the prescribed addition Add is preferably greater than or equal to 0.5 diopter, and smaller than or equal to 5 diopters, for example smaller than or equal to 4 diopters.
  • the ophthalmic progressive addition lens according to the invention has in given wearing conditions at least:
  • the ophthalmic progressive addition lens according to the invention further comprises a far vision (distant) reference point and a near vision (distant) reference point.
  • the meridian line of an ophthalmic lens according to the invention has an inset greater than or equal to 3°, for example greater than or equal to 4°.
  • the ophthalmic progressive addition lens is arranged so that in the given wearing conditions the optical power in the gaze direction corresponding to the fitting cross is greater than or equal to 5% of the prescribed addition and smaller than or equal to 10% of the prescribed addition.
  • the level of symmetry of the optical design with respect to the meridian line over the domain of gaze directions may be characterized based on the difference of optical power on each side of the meridian.
  • MaxSymPpo is preferably smaller than or equal to 0.12* Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for a hyperopic wearer.
  • a hyperopic wearer is a wearer having an average optical power for far vision distance greater than 0.75 diopter.
  • MaxSymPpo is preferably smaller than or equal to 0.12*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for an emmetropic wearer.
  • An emmetropic wearer is wearer having an average optical power for far vision distance greater than - 0.75 diopter and smaller than 0.75 diopters.
  • MaxSymPpo is preferably smaller than or equal to 0.09*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for myopic wearer.
  • a myopic wearer is wearer having an average optical power for far vision distance smaller than - 0.75 diopter.
  • MaxSymPpo is preferably smaller than or equal to 0.09*Add.
  • the n couples of gaze directions may be obtained by sampling the domain of gaze directions with a constant angular step.
  • the angular step is determined so as to have at least 100 couples of gaze directions.
  • the angular step may be oversampling the domain of gaze directions and selecting at least 100 couples of gaze directions.
  • n couples of gaze directions are considered evenly distributed over a domain of gaze directions of radius r if over each sub-domain of gaze directions included in said domain of gaze directions and corresponding to a circle of radius r/4 the density of gaze directions is greater than or equal to 90% of the density over the domain of gaze directions and smaller than or equal to 110% of the density over the domain of gaze directions.
  • RMSSymPpo is preferably smaller than or equal to 0.06*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for a hyperopic wearer.
  • a hyperopic wearer RMSSymPpo is preferably smaller than or equal to 0.06*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for an emmetropic wearer.
  • RMSSymPpo is preferably smaller than or equal to 0.04*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for myopic wearer.
  • MaxSymPpo is preferably smaller than or equal to 0.04*Add.
  • the level of symmetry of the optical design with respect to the meridian line over the domain of gaze directions may be characterized based on the difference of unwanted astigmatism on each side of the meridian.
  • MaxSymAsr is smaller than or equal to 0.12*Add, in particular when the ophthalmic progressive addition lens according to the invention is adapted for a hyperopic wearer.
  • MaxSymAsr is preferably smaller than or equal to
  • MaxSymAsr is preferably smaller than or equal to
  • optical function of the ophthalmic progressive addition lens according to the invention may be characterized by RMSSymAsr, with
  • RMSSymAsr with GapAsr, being defined for two gaze directions
  • RMSSymAsr is preferably smaller than or equal to 0.06*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for a hyperopic wearer.
  • an ophthalmic progressive addition lens adapted for a hyperopic wearer RMSSymAsr is preferably smaller than or equal to 0.06*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for an emmetropic wearer.
  • RMSSymAsr is preferably smaller than or equal to 0.04*Add.
  • the ophthalmic progressive addition lens according to the invention may be adapted for myopic wearer.
  • an ophthalmic progressive addition lens adapted for a myopic wearer RMSSymAsr is preferably smaller than or equal to 0.04*Add.
  • the module of unwanted astigmatism over the domain of gaze directions is smaller than or equal to the prescribed addition of the wearer.
  • the difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°, for example smaller than or equal to 26°.
  • Figures 4a to 4c show the optical features of an ophthalmic progressive addition lens according to the invention in standard wearing conditions.
  • the ophthalmic progressive addition lens is adapted for a wearer having a plane prescription with an addition of 2.5 diopters.
  • Figure 4a a shows refractive power along the meridian.
  • the x-axes are graduated in diopters, and the y-axes give the angle a, in degrees.
  • Figure 4b shows, using the same axes, lines of equal module of unwanted astigmatism.
  • the step of the module of unwanted astigmatism optical power between two lines is 0.25 diopter.
  • Figure 4c shows lines of equal optical power, i.e. lines formed by points for which power has an identical value.
  • the x-axis and y-axis respectively give the angles a and b in degrees.
  • the step of optical power between two lines is 0.25 diopter.
  • Figures 5a to 5c show the optical features of an ophthalmic progressive addition lens according to the invention in standard wearing conditions.
  • the ophthalmic progressive addition lens is adapted for a wearer having a plane prescription with an addition of 2.0 diopters.
  • Figure 5a a shows refractive power along the meridian.
  • the x-axes are graduated in diopters, and the y-axes give the angle a, in degrees.
  • Figure 5b shows lines of equal optical power, i.e. lines formed by points for which power has an identical value.
  • the x-axis and y-axis respectively give the angles a and b in degrees.
  • the step of optical power between two lines is 0.25 diopter.
  • Figure 5c shows, using the same axes, lines of equal module of unwanted astigmatism.
  • the step of the module of unwanted astigmatism optical power between two lines is 0.25 diopter.
  • the invention further relates to a method, for example implemented by computer means, for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add.
  • the method for determining an optical function comprises at least:
  • the inset value may be received for a distant entity, retrieved from a database, measured directly on the wearer, calculated, for example according to the prescription and ray-tracing calculation algorithms or obtain with any other means known by the person skilled in the art.
  • the optical function determined has:
  • the optical function of the optical lens may be determined so that MaxSymPpo is smaller than or equal to 0.12*Add or smaller than or equal to 0.09*Add for an emmetropic wearer or smaller than or equal to 0.09*Add for a myopic wearer.
  • the optical function of the optical lens may be determined so that MaxSymAsr is smaller than or equal to 0.12*Add or smaller than or equal to 0.09*Add for an emmetropic wearer or smaller than or equal to 0.09*Add for a myopic wearer.
  • the optical function of the optical lens may be determined so that RMSSymPpo is smaller than or equal to 0.06* Add or smaller than or equal to 0.03* Add for an emmetropic wearer or smaller than or equal to 0.04*Add for a myopic wearer.
  • the optical function of the optical lens may be determined so that RMSSymAsr is smaller than or equal to 0.06* Add or smaller than or equal to 0.03* Add for an emmetropic wearer or smaller than or equal to 0.04*Add for a myopic wearer.
  • the optical function is determined so that in the given wearing conditions having a difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°.
  • the invention further relates to a method of obtaining an ophthalmic progressive addition lens adapted for a wearer having a prescribe addition Add, the method comprising the steps of the method of determining an optical function according to the invention and further comprises manufacturing an ophthalmic lens having the determined optical function.
  • the manufacturing may comprise any known manufacturing technique such a machining, polishing, molding, additive manufacturing.

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Abstract

An ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, said progressive ophthalmic lens having in given wearing conditions: - a meridian line with an inset greater than or equal to 3°, - a fitting cross FC (αFC, βFC), and - an optical function symmetrical with respect to said meridian line in said given wearing conditions at least over a domain of gaze directions (α, β) joining the center of rotation of the eye of the wearer and the lens, where α is a lowering angle in degree and β is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in α = 8° and β = 0° and where the optical power in the gaze direction corresponding to the fitting cross is greater than or equal to 5% of the prescribed addition.

Description

An ophthalmic progressive addition lens adapted for a wearer
FIELD OF THE INVENTION The invention relates to an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition. The invention further relates to a method for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition. BACKGROUND OF THE INVENTION
Usually, when determining an ophthalmic lens adapted for a wearer, prescription data are considered. The ophthalmic lenses, in particular progressive additional ophthalmic lenses may comprise optical aberrations such as unwanted astigmatism resulting from the optical design of the ophthalmic lens. The lens designer may modify the optical design so as to try to reduce optical aberrations such as unwanted astigmatism however in some cases such optical aberrations cannot be totally avoided. In some other cases reducing the unwanted astigmatism requires reducing the optical performance of the ophthalmic lens.
In such cases the optical design of the lens may be adapted to change the distribution of the optical aberrations so as to adapt the optical design to the wearer.
Furthermore, most ophthalmic lenses are intended to be provided in pairs, one for the right eye and one for the left eye. The optical design should be adapted to provide good binocular vision to the wearer.
Therefore, there is a need for ophthalmic progressive addition lens adapted for a wearer having a prescribed addition and providing improved binocular performances.
One object of the present invention is to provide such an ophthalmic progressive addition lens. SUMMARY OF THE INVENTION
To this end, the invention proposes an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, said progressive ophthalmic lens having in given wearing conditions:
- a meridian line with an inset greater than or equal to 3°,
- a fitting cross FC (OIFC, PFC), and
- an optical function symmetrical with respect to said meridian line in said given wearing conditions at least over a domain of gaze directions (a, b) joining the center of rotation of the eye of the wearer and the lens, where a is a lowering angle in degree and b is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in a = 8° and b = 0°, and
where the optical power in the gaze direction corresponding to the fitting cross is greater than or equal to 5% of the prescribed addition.
Advantageously, having an optical function symmetrical with respect to the meridian line at least over the domain of gaze directions mostly used by the wearer when wearing the progressive addition lens greatly improves the binocular vision of the wearer.
Furthermore, having an optical power greater than or equal to 5% of the prescribed addition at the fitting cross allows a softer progression of the optical power along the meridian, increasing the vision comfort of the wearer.
According to further embodiments which can be considered alone or in combination:
- MaxSymPpo is smaller than or equal to 0.12* Add, with
MaxSymPpo = max GapPpo, , with GapPpo, being defined for two gaze
i= l,...,n
directions Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle a, and having different azimuth angle bί, the different angles bi of Ai and Bi having an equal azimuth angular distance bi relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapPpo, = ABS(Ppo(Aj)— Ppo(Bj)) with Ppo the optical power at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100 , the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions; and/or
- the ophthalmic progressive addition lens is adapted for a hyperopic wearer; and/or
- the ophthalmic progressive addition lens is adapted for an emmetropic wearer and MaxSymPpo is smaller than or equal to 0.09*Add; and/or
- the ophthalmic progressive addition lens is adapted for a myopic wearer and MaxSymPpo is smaller than or equal to 0.09*Add; and/or
- MaxSymAsr is smaller than or equal to 0.12*Add, with
MaxSymAsr = max GapAsr, , with GapAsr, being defined for two gaze
i= l,...,n
directions Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle and having different azimuth angle bί, the different angles bi of Ai and Bi having an equal azimuth angular distance bί, relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapAsr, = ABS(Asr(Aj)— Asr(Bj)) with Asr the unwanted astigmatism at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100 , the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions; and/or
- the ophthalmic progressive addition lens is adapted for a hyperopic wearer; and/or
- the ophthalmic progressive addition lens is adapted for an emmetropic wearer and MaxSymAsr is smaller than or equal to 0.09*Add; and/or
- the ophthalmic progressive addition lens is adapted for a myopic wearer and MaxSymAsr is smaller than or equal to 0.09*Add; and/or
- RMSSymPpo is smaller than or equal to 0.06*Add, with being defined for two gaze directions Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapPpo, = ABS(Ppo(Aj)— Ppo(Bj)) with Ppo the optical power at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100 , the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions; and/or
- the ophthalmic progressive addition lens is adapted for a hyperopic wearer; and/or
- the ophthalmic progressive addition lens is adapted for an emmetropic wearer and RMSSymPpo is smaller than or equal to 0.04*Add; and/or
- the ophthalmic progressive addition lens is adapted for a myopic wearer and RMSSymPpo is smaller than or equal to 0.04*Add; and/or
- RMSSymAsr is smaller than or equal to 0.06*Add, with being defined for two gaze
Figure imgf000006_0001
directions Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapAsr, = ABS(Asr(Aj)— Asr(Bj)) with Asr the unwanted astigmatism at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions; and/or - the ophthalmic progressive addition lens is adapted for a hyperopic wearer; and/or
- the ophthalmic progressive addition lens is adapted for an emmetropic wearer and RMSSymAsr is smaller than or equal to 0.04*Add; and/or
- the ophthalmic progressive addition lens is adapted for a myopic wearer and RMSSymAsr is smaller than or equal to 0.04*Add; and/or
- the module of unwanted astigmatism in the given wearing conditions is smaller than or equal to the prescribed addition of the wearer at least over said domain of gaze directions (a, b); and/or
- in the given wearing conditions the difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°; and/or
- the given wearing conditions are standard wearing conditions; and/or
- the given wearing conditions are customized wearing condition; and/or
- the prescribed addition is greater than or equal to 0.50 Diopter, and smaller than or equal to 5 Diopters, for example smaller than or equal to 4 Diopters.
The invention also relates to a pair of ophthalmic progressive addition lenses, wherein each ophthalmic progressive addition lens is according to the invention.
According to a further aspect, the invention relates to a method, for example implemented by computer means, for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, comprising:
- obtaining an inset value, and
- determining in given wearing condition the optical function having:
• a meridian line with an inset corresponding to the obtained inset value and being symmetrical with respect to said meridian line in said given wearing conditions at least over a domain of gaze directions (a, b) joining the center of rotation of the eye of the wearer and the lens, where a is a lowering angle in degree and b is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in a = 8° and b = 0°, and
• an optical power in the gaze direction corresponding to the fitting cross greater than or equal to 5% of the prescribed addition.
According to an embodiment of the method of the invention the optical function is determined so that the module of unwanted astigmatism in the given wearing conditions is smaller than or equal to the prescribed addition of the wearer at least over said domain of gaze directions (a, b).
According to a further embodiment of the method of the invention the optical function is determined so as to further comprise a fitting cross FC (OIFC, bk ) and in the given wearing conditions having a difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°.
The invention also relates to a method of obtaining an ophthalmic progressive addition lens adapted for a wearer having a prescribe addition Add, the method comprising the steps of the method of determining an optical function of an ophthalmic progressive addition lens according to the invention and further comprises manufacturing an ophthalmic lens having the determined optical function.
The invention further relates to a computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, causes the processor to carry out the steps of the methods according to the invention.
The invention also relates to a computer-readable storage medium having a program recorded thereon; where the program makes the computer execute the method of the invention.
The invention further relates to a device comprising a processor adapted to store one or more sequence of instructions and to carry out at least one of the steps of the method according to the invention.
Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "computing", "calculating", or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.
Embodiments of the present invention may include apparatuses for performing the operations herein. These apparatuses may be specially constructed for the desired purposes, or it may comprise a general purpose computer or Digital Signal Processor ("DSP") selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs) electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the desired method. The desired structure for a variety of these systems will appear from the description below. In addition, embodiments of the present invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the inventions as described herein.
BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figures 1 and 2 show, diagrammatically, optical systems of eye and lens and ray tracing from the center of rotation of the eye;
Figure 3 shows the field vision zones of an ophthalmic progressive addition lens;
Figures 4 and 5 illustrate examples of optical functions of ophthalmic progressive addition lenses according to the invention.
DEFINITIONS
The following definitions are provided so as to define the wordings used within the frame of the present invention.
The wordings "wearer's prescription", also called "prescription data", are known in the art. Prescription data refers to one or more data obtained for the wearer and indicating for at least an eye, preferably for each eye, a prescribed sphere SPHp, and/or a prescribed astigmatism value CYLp and a prescribed axis AXISp suitable for correcting the ametropia of each eye for the wearer and a prescribed addition Add suitable for correcting the presbyopia of each of his eyes. The prescribed addition is transmitted by the ECP when he/she orders the lens to a lens manufacturer. The lens manufacturer prescribed addition usually inscribes information relative to the prescribed addition on the paper packaging of the delivered lens. The prescribed addition may be also determined from engravings located on the lens and still visible after the lens is edged and when mounted in said spectacle frame chosen by the wearer.
"Progressive ophthalmic addition lenses" are known in the art. According to the invention, the lens may be a standard type lens but also a lens for information glasses, wherein the lens comprises means for displaying information in front of the eye. The lens may also be suitable for sunglasses or not. All ophthalmic lenses of the invention may be paired so as to form a pair of lenses (left eye LE, right eye RE).
The wording“optical design” is a widely used wording known from the man skilled in the art in ophthalmic domain to designate the set of parameters allowing to defining a dioptric function of an ophthalmic lens; each ophthalmic lens designer has its own designs, particularly for progressive ophthalmic lenses. As for an example, a progressive ophthalmic lens“design” results of an optimization of a progressive -Si- surface so as to restore a presbyope’s ability to see clearly at all distances but also to optimally respect all physiological visual functions such as foveal vision, extra-foveal vision, binocular vision, dynamic vision and to minimize unwanted astigmatisms. For example, a progressive lens design comprises:
- a power profile along the main gaze directions (meridian line) used by the lens wearer during day life activities,
- distributions of powers (mean power, astigmatism,...) on the sides of the lens, that is to say away from the main gaze direction.
These optical characteristics are part of the "designs" defined and calculated by ophthalmic lens designers and that are provided with the progressive lenses.
A "gaze direction" is identified by a couple of angle values (a,b), wherein said angles values are measured with regard to reference axes centered on the center of rotation of the eye, commonly named as "CRE". More precisely, figure 1 represents a perspective view of such a system illustrating parameters a and b used to define a gaze direction.
Figure 2 is a view in the vertical plane parallel to the antero-posterior axis of the wearer's head and passing through the center of rotation of the eye in the case when the parameter b is equal to 0. The center of rotation of the eye is labeled CRE. The axis CRE-F', shown on Figure 2 in a dot-dash line, is the horizontal axis passing through the center of rotation of the eye and extending in front of the wearer - that is the axis CRE-F' corresponding to the primary gaze direction. The lens is placed and centered in front of the eye such that the axis CRE-F' cuts the front surface of the lens on a point called the fitting cross, which is, in general, present on lenses to enable the positioning of lenses in a frame by an optician. The fitting cross is point on a lens as specified by the manufacturer to be used as a reference point for positioning the lens in front of a wearer’s eye. The fitting cross is defined by the norm ISO 8980-2, Ophthalmic Optics. The point of intersection of the rear surface of the lens and the axis CRE-F' is the point, O. A vertex sphere, which center is the center of rotation of the eye, CRE, and has a radius q' = O-CRE, intercepts the rear surface of the lens in a point of the horizontal axis. A value of radius q' of 25.5 mm corresponds to a usual value and provides satisfying results when wearing the lenses. Other value of radius q' may be chosen. A given gaze direction, represented by a solid line on figure 1, corresponds to a position of the eye in rotation around CRE and to a point J (see figure 2) of the vertex sphere.
The angle b is the angle formed between the axis CRE-F' and the projection of the straight line CRE-J on the horizontal plane comprising the axis CRE-F'; this angle appears on the scheme on Figure 1.
The angle a is the angle formed between the axis CRE-J and the projection of the straight line CRE-J on the horizontal plane comprising the axis CRE-F'; this angle appears on the scheme on Figures 1 and 2.
A given gaze view thus corresponds to a point J of the vertex sphere or to a couple (a,b). The more the value of the lowering gaze angle is positive, the more the gaze is lowering and the more the value is negative, the more the gaze is rising. In a given gaze direction, the image of a point M in the object space, located at a given object distance, is formed between two points S and T corresponding to minimum and maximum distances JS and JT, which would be the sagittal and tangential local focal lengths. The image of a point in the object space at infinity is formed, at the point F'. The distance D corresponds to the rear frontal plane of the lens.
For each gaze direction (a,b), a mean refractive power RRO(a,b), a module of astigmatism ASR(a^) and an axis ACE(a,b) of this astigmatism, and a module of resulting (also called residual or unwanted) astigmatism ASR(a^) are defined.
"Astigmatism" refers to astigmatism generated by the lens, or to residual astigmatism (resulting astigmatism) which corresponds to the difference between the prescribed astigmatism (wearer astigmatism) and the lens-generated astigmatism; in each case, with regards to amplitude or both amplitude and axis.
In the sense of the invention, an“optical function” corresponds to a function providing for each gaze direction the effect of an optical lens on the light ray passing through the optical lens.
The optical function may comprise dioptric function, light absorption, polarizing capability, reinforcement of contrast capacity, etc...
The dioptric function corresponds to the optical lens power (mean power, astigmatism etc... ) as a function of the gaze direction.
"Ergorama" is a function associating to each gaze direction the usual distance of an object point. Typically, in far vision following the primary gaze direction, the object point is at infinity. In near vision, following a gaze direction essentially corresponding to an angle a of the order of 35° and to an angle b of the order of 5° in absolute value towards the nasal side, the object distance is of the order of 30 to 50 cm. For more details concerning a possible definition of an ergorama, US patent US A-6, 318,859 may be considered. This document describes an ergorama, its definition and its modeling method.
For the purpose of the invention, points may be at infinity or not. Ergorama may be a function of the wearer's ametropia. Using these elements, it is possible to define a wearer optical power and astigmatism, in each gaze direction. An object point M at an object distance given by the ergorama is considered for a gaze direction (a,b). An object proximity ProxO is defined for the point M on the corresponding light ray in the object space as the inverse of the distance MJ between point M and point J of the vertex sphere: ProxO=l /MJ
This enables to calculate the object proximity within a thin lens approximation for all points of the vertex sphere, which is used for the determination of the ergorama. For a real lens, the object proximity can be considered as the inverse of the distance between the object point and the front surface of the lens, on the corresponding light ray.
For the same gaze direction (a,b), the image of a point M having a given object proximity is formed between two points S and T which correspond respectively to minimal and maximal focal distances (which would be sagittal and tangential focal distances). The quantity Proxl is called image proximity of the point M:
Figure imgf000013_0001
By analogy with the case of a thin lens, it can therefore be defined, for a given gaze direction and for a given object proximity, i.e. for a point of the object space on the corresponding light ray, an optical power PPO as the sum of the image proximity and the object proximity.
PPO = ProxO + Proxl
The optical power is also called refractive power.
With the same notations, an astigmatism AST is defined for every gaze direction and for a given object proximity 1 1
AST =
JT Is
This definition corresponds to the astigmatism of a ray beam created by the lens. The resulting astigmatism ASR is defined for every gaze direction through the lens as the difference between the actual astigmatism value AST for this gaze direction and the prescribed astigmatism. The residual astigmatism (resulting astigmatism) ASR more precisely corresponds to module of the vectorial difference between actual (AST, AXE) and prescription data (CYLp, AXISp).
When the characterization of the lens is of optical kind, it refers to the ergorama-eye-lens system described above. For simplicity, the term lens' is used in the description but it has to be understood as the 'ergorama-eye-lens system'. The values in optic terms can be expressed for gaze directions. Conditions suitable to determine of the ergorama-eye-lens system are called in the frame present invention "given wearing conditions".
The given wearing conditions are to be understood as the position of the lens element with relation to the eye of a wearer, for example defined by a pantoscopic angle, a cornea to lens distance, a pupil-cornea distance, a center of rotation of the eye to pupil distance, a center of rotation of the eye to lens distance and a wrap angle.
In the remainder of the description, terms like « up », « bottom », «horizontal», « vertical », « above », « below », or other words indicating relative position may be used. These terms are to be understood in the wearing conditions of the lens. Notably, the "upper" part of the lens corresponds to a negative lowering angle a <0° and the "lower" part of the lens corresponds to a positive lowering angle a >0°.
A "far-vision gaze direction", referred as FVGD, is defined for a lens, as the vision gaze direction corresponding to the far vision (distant) reference point and thus (CIFV, FV), where the mean refractive power is substantially equal to the mean prescribed power in far vision, the mean prescribed power being equal to SPHp+(CYFp/2). Within the present disclosure, far-vision is also referred to as distant-vision. In the sense of the invention far vision is to be understood as vision at a distance greater than or equal to 4 meters. A "near-vision gaze direction", referred as NVGD, is defined for a lens, as the vision gaze direction corresponding to the near vision (reading) reference point, and thus (OINV,PNV) where the refractive power is substantially equal to the prescribed power in far vision plus the prescribed addition Add. In the sense of the invention near vision is to be understood as vision at a distance smaller than or equal to 50 cm. Here “substantially equal” means a“equal with a tolerance lower than 15%”.
A "fitting-cross gaze direction", referred as FCGD, is defined for a lens, as the vision gaze direction corresponding to the fitting cross reference point and (ai o,bk )·
The "meridian line", referred as ML(a,P), of a progressive addition lens is a line defined from top to bottom of the lens and passing through the fitting cross where one can see clearly an object point. Said meridian line is defined on the basis of the repartition of module of resulting astigmatism, ASR, over the (a, b) domain and substantially correspond to the center of the two central iso-module of resulting astigmatism values which value is equal to 0. 5 Diopter. To be more specific and according to the present invention the meridian line is calculated according to following method:
- One defines the gaze direction, FCGD, corresponding to the fitting cross (CIFC^FC),
- One calculates the lowering angle OINV corresponding to the near vision gaze direction;
- For each lowering angle a comprised between (XFC and OINV, one calculates the azimuth angle b corresponding to the midway direction between the two central iso module of resulting astigmatism values which value is equal to 0.5 Diopter; said calculated directions are referred as (¾, bq;
- The meridian line is defined as the curve passing through the following points:
Figure imgf000015_0001
"Micro-markings" also called "alignment reference marking" have been made mandatory on progressive lenses by the harmonized standards ISO 13666:2012 ("Alignment reference marking: permanent markings provided by the manufacturer to establish the horizontal alignment of the lens or lens blank, or to re-establish other reference points") and ISO 8980-2 ("Permanent marking: the lens has to provide at least following permanent markings: alignment reference markings comprising two markings distant from 34 mm one of each other, equidistant from a vertical plane passing through the fitting cross or the prism reference point"). Micro-markings that are defined the same way are also usually made on complex surfaces, such as on a front surface of a lens with a front surface comprising a progressive or regressive front surface.
"Temporary markings" may also be applied on at least one of the two surfaces of the lens, indicating positions of control points (reference points) on the lens, such as a control point for far- vision, a control point for near-vision, a prism reference point and a fitting cross for instance. The prism reference point PRP is considered here at the midpoint of the straight segment which connects the micro-markings. If the temporary markings are absent or have been erased, it is always possible for a skilled person to position the control points on the lens by using a mounting chart and the permanent micro-markings. Similarly, on a semi-finished lens blank, standard ISO 10322-2 requires micro-markings to be applied. The centre of the aspherical surface of a semi-finished lens blank can therefore be determined as well as a referential as described above.
Figure 3 shows field vision zones of an ophthalmic progressive addition lens 30 where said lens comprises a far vision (distant vision) zone 32 located in the upper part of the lens, a near vision zone 36 located in the lower part of the lens and an intermediate zone 34 situated between the far vision zone 32 and the near vision zone 36. The meridian line is referred as 38.
As illustrated on figure 3 in a progressive addition lens, the near-vision point can be shifted horizontally with respect to a vertical line passing through the distance- vision point, when the lens is in wearing conditions. This shift, which is in the direction of the nasal side of the lens, is usually referred to as“inset” and its value may be expressed as the \bNn ~ I ·
The“wearing conditions” are to be understood as the position of the ophthalmic lens with relation to the eye of a wearer, for example defined by a pantoscopic angle, a Cornea to lens distance, a Pupil-cornea distance, a CRE to pupil distance, a CRE to lens distance and a wrap angle.
The Cornea to lens distance is the distance along the visual axis of the eye in the primary position (usually taken to be the horizontal) between the cornea and the back surface of the lens ; for example equal to 12mm.
The Pupil-cornea distance is the distance along the visual axis of the eye between its pupil and cornea ; usually equal to 2mm.
The CRE to pupil distance is the distance along the visual axis of the eye between its center of rotation (CRE) and cornea ; for example equal to 11.5mm.
The CRE to lens distance is the distance along the visual axis of the eye in the primary position (usually taken to be the horizontal) between the CRE of the eye and the back surface of the lens, for example equal to 25.5mm.
The Pantoscopic angle is the angle in the vertical plane, at the intersection between the back surface of the lens and the visual axis of the eye in the primary position (usually taken to be the horizontal), between the normal to the back surface of the lens and the visual axis of the eye in the primary position ; for example equal to 8
The wrap angle is the angle in the horizontal plane, at the intersection between the back surface of the lens and the visual axis of the eye in the primary position (usually taken to be the horizontal), between the normal to the back surface of the lens and the visual axis of the eye in the primary position for example equal to 0°.
An example of standard wearer condition may be defined by a pantoscopic angle of -8°, a Cornea to lens distance of 12 mm, a Pupil-cornea distance of 2 mm, a CRE to pupil distance of 11.5 mm, a CRE to lens distance of 25.5 mm and a wrap angle of 0°.
Other wearing conditions may be used. Wearing conditions may be calculated from a ray-tracing program, for a given lens.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add. The prescribed addition Add is preferably greater than or equal to 0.5 diopter, and smaller than or equal to 5 diopters, for example smaller than or equal to 4 diopters.
The ophthalmic progressive addition lens according to the invention has in given wearing conditions at least:
- a meridian line,
- a fitting cross FC (OIFC, bi C), and
- an optical function symmetrical with respect to said meridian line.
According to a preferred embodiment of the invention the ophthalmic progressive addition lens according to the invention further comprises a far vision (distant) reference point and a near vision (distant) reference point.
The meridian line of an ophthalmic lens according to the invention has an inset greater than or equal to 3°, for example greater than or equal to 4°.
The ophthalmic progressive addition lens according is arranged so that in the given wearing conditions the optical power in the gaze direction corresponding to the fitting cross is greater than or equal to 5% of the prescribed addition and smaller than or equal to 10% of the prescribed addition.
The optical function of the ophthalmic progressive addition lens according to the invention is symmetrical with respect to the meridian line at least over a domain of gaze directions (a, b) joining the center of rotation of the eye of the wearer and the lens, where a is a lowering angle in degree and b is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in a = 8° and b = 0°.
The level of symmetry of the optical design with respect to the meridian line over the domain of gaze directions may be characterized based on the difference of optical power on each side of the meridian.
For example, the optical function of the ophthalmic progressive addition lens according to the invention may be characterized by MaxSymPpo, with MaxSymPpo = max GapPpo, with GapPpo, being defined for two gaze directions
i= l,...,n
Ai and Bi, respectively defines a couple of coordinate defined domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapPpOj = ABS(Ppo(Aj)— Ppo(Bj)) with Ppo the optical power at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
In general, MaxSymPpo is preferably smaller than or equal to 0.12* Add.
In particular the ophthalmic progressive addition lens according to the invention may be adapted for a hyperopic wearer. A hyperopic wearer is a wearer having an average optical power for far vision distance greater than 0.75 diopter. In the case of an ophthalmic progressive addition lens adapted for a hyperopic wearer MaxSymPpo is preferably smaller than or equal to 0.12*Add.
Alternatively, the ophthalmic progressive addition lens according to the invention may be adapted for an emmetropic wearer. An emmetropic wearer is wearer having an average optical power for far vision distance greater than - 0.75 diopter and smaller than 0.75 diopters. In the case of an ophthalmic progressive addition lens adapted for an emmetropic wearer MaxSymPpo is preferably smaller than or equal to 0.09*Add.
Alternatively, the ophthalmic progressive addition lens according to the invention may be adapted for myopic wearer. A myopic wearer is wearer having an average optical power for far vision distance smaller than - 0.75 diopter. In the case of an ophthalmic progressive addition lens adapted for a myopic wearer MaxSymPpo is preferably smaller than or equal to 0.09*Add.
The optical function of the ophthalmic progressive addition lens according to the invention may be characterized by RMSSymPpo, with RMSSymPpo = ~å GapPpOj 2, with GapPpo, being defined for two gaze directions Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle bi, the different angles bi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapPpOj = ABS(Ppo(Aj)— Ppo(Bj)) with Ppo the optical power at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
For example, the n couples of gaze directions (Ai, Bi) may be obtained by sampling the domain of gaze directions with a constant angular step. The angular step is determined so as to have at least 100 couples of gaze directions. For example, the angular step may be oversampling the domain of gaze directions and selecting at least 100 couples of gaze directions.
In the sense of the invention, n couples of gaze directions (Ai, Bi) are considered evenly distributed over a domain of gaze directions of radius r if over each sub-domain of gaze directions included in said domain of gaze directions and corresponding to a circle of radius r/4 the density of gaze directions is greater than or equal to 90% of the density over the domain of gaze directions and smaller than or equal to 110% of the density over the domain of gaze directions.
In general, RMSSymPpo is preferably smaller than or equal to 0.06*Add.
In particular the ophthalmic progressive addition lens according to the invention may be adapted for a hyperopic wearer. In the case of an ophthalmic progressive addition lens adapted for a hyperopic wearer RMSSymPpo is preferably smaller than or equal to 0.06*Add.
Alternatively, the ophthalmic progressive addition lens according to the invention may be adapted for an emmetropic wearer. In the case of an ophthalmic progressive addition lens adapted for an emmetropic wearer RMSSymPpo is preferably smaller than or equal to 0.04*Add.
Alternatively, the ophthalmic progressive addition lens according to the invention may be adapted for myopic wearer. In the case of an ophthalmic progressive addition lens adapted for a myopic wearer MaxSymPpo is preferably smaller than or equal to 0.04*Add.
The level of symmetry of the optical design with respect to the meridian line over the domain of gaze directions may be characterized based on the difference of unwanted astigmatism on each side of the meridian. For example, the optical function of the ophthalmic progressive addition lens according to the invention may be characterized by MaxSymAsr, with MaxSymAsr = max GapAsr, with GapAsr, being defined for two gaze directions Ai and Bi, i=l,...,n
respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ to the meridian line, Ai and Bi being located on each side of the meridian line as GapAsr, = ABS(Asr(Aj)— Asr(Bj)) with Asr the unwanted astigmatism at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
In general, MaxSymAsr is smaller than or equal to 0.12*Add, in particular when the ophthalmic progressive addition lens according to the invention is adapted for a hyperopic wearer.
When the ophthalmic progressive addition lens according to the invention is adapted for an emmetropic wearer, MaxSymAsr is preferably smaller than or equal to
0.09*Add.
When the ophthalmic progressive addition lens according to the invention is adapted for a myopic wearer, MaxSymAsr is preferably smaller than or equal to
0.09*Add.
The optical function of the ophthalmic progressive addition lens according to the invention may be characterized by RMSSymAsr, with
RMSSymAsr = with GapAsr, being defined for two gaze directions
Figure imgf000021_0001
Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapAsr, = ABS(Asr(Aj)— Asr(Bj)) with Asr the unwanted astigmatism at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
In general, RMSSymAsr is preferably smaller than or equal to 0.06*Add.
In particular the ophthalmic progressive addition lens according to the invention may be adapted for a hyperopic wearer. In the case of an ophthalmic progressive addition lens adapted for a hyperopic wearer RMSSymAsr is preferably smaller than or equal to 0.06*Add.
Alternatively, the ophthalmic progressive addition lens according to the invention may be adapted for an emmetropic wearer. In the case of an ophthalmic progressive addition lens adapted for an emmetropic wearer RMSSymAsr is preferably smaller than or equal to 0.04*Add.
Alternatively, the ophthalmic progressive addition lens according to the invention may be adapted for myopic wearer. In the case of an ophthalmic progressive addition lens adapted for a myopic wearer RMSSymAsr is preferably smaller than or equal to 0.04*Add.
So as to reduce the potential difference between right and left ophthalmic progressive addition lenses according to the invention, the module of unwanted astigmatism over the domain of gaze directions is smaller than or equal to the prescribed addition of the wearer.
So as to maintain an easy access to the near vision power and a comfortable near vision usage, it is preferable to reduce the overall progression length of the optical function of the ophthalmic progressive addition lens according to the invention. Therefore, according to an embodiment of the invention in the given wearing conditions the difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°, for example smaller than or equal to 26°. Figures 4a to 4c show the optical features of an ophthalmic progressive addition lens according to the invention in standard wearing conditions. The ophthalmic progressive addition lens is adapted for a wearer having a plane prescription with an addition of 2.5 diopters.
Figure 4a a shows refractive power along the meridian. The x-axes are graduated in diopters, and the y-axes give the angle a, in degrees.
Figure 4b shows, using the same axes, lines of equal module of unwanted astigmatism. The step of the module of unwanted astigmatism optical power between two lines is 0.25 diopter.
Figure 4c shows lines of equal optical power, i.e. lines formed by points for which power has an identical value. The x-axis and y-axis respectively give the angles a and b in degrees. The step of optical power between two lines is 0.25 diopter.
Figures 5a to 5c show the optical features of an ophthalmic progressive addition lens according to the invention in standard wearing conditions. The ophthalmic progressive addition lens is adapted for a wearer having a plane prescription with an addition of 2.0 diopters.
Figure 5a a shows refractive power along the meridian. The x-axes are graduated in diopters, and the y-axes give the angle a, in degrees.
Figure 5b shows lines of equal optical power, i.e. lines formed by points for which power has an identical value. The x-axis and y-axis respectively give the angles a and b in degrees. The step of optical power between two lines is 0.25 diopter.
Figure 5c shows, using the same axes, lines of equal module of unwanted astigmatism. The step of the module of unwanted astigmatism optical power between two lines is 0.25 diopter.
The invention further relates to a method, for example implemented by computer means, for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add.
The method for determining an optical function comprises at least:
-obtaining an inset value, and
- determining in given wearing condition the optical function.
In the sense of the invention the inset value may be received for a distant entity, retrieved from a database, measured directly on the wearer, calculated, for example according to the prescription and ray-tracing calculation algorithms or obtain with any other means known by the person skilled in the art.
The optical function determined has:
• a meridian line with an inset corresponding to the obtained inset value and being symmetrical with respect to said meridian line in said given wearing conditions at least over a domain of gaze directions (a, b) joining the center of rotation of the eye of the wearer and the lens, where a is a lowering angle in degree and b is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in a = 8° and b = 0°, and
• and an optical power in the gaze direction corresponding to the fitting cross greater than or equal to 5% of the prescribed addition.
The optical function of the optical lens may be determined so that MaxSymPpo is smaller than or equal to 0.12*Add or smaller than or equal to 0.09*Add for an emmetropic wearer or smaller than or equal to 0.09*Add for a myopic wearer.
The optical function of the optical lens may be determined so that MaxSymAsr is smaller than or equal to 0.12*Add or smaller than or equal to 0.09*Add for an emmetropic wearer or smaller than or equal to 0.09*Add for a myopic wearer.
The optical function of the optical lens may be determined so that RMSSymPpo is smaller than or equal to 0.06* Add or smaller than or equal to 0.03* Add for an emmetropic wearer or smaller than or equal to 0.04*Add for a myopic wearer.
The optical function of the optical lens may be determined so that RMSSymAsr is smaller than or equal to 0.06* Add or smaller than or equal to 0.03* Add for an emmetropic wearer or smaller than or equal to 0.04*Add for a myopic wearer.
According to an embodiment of the method of the invention the optical function is determined so that in the given wearing conditions having a difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°.
The invention further relates to a method of obtaining an ophthalmic progressive addition lens adapted for a wearer having a prescribe addition Add, the method comprising the steps of the method of determining an optical function according to the invention and further comprises manufacturing an ophthalmic lens having the determined optical function.
The manufacturing may comprise any known manufacturing technique such a machining, polishing, molding, additive manufacturing.
The invention has been described above with the aid of embodiments without limitation of the general inventive concept.
Many further modifications and variations will suggest themselves to those skilled in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims.
In the claims, the word“comprising” does not exclude other elements or steps, and the indefinite article“a” or“an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

1. An ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, said progressive ophthalmic lens having in given wearing conditions:
- a meridian line with an inset greater than or equal to 3°,
- a fitting cross FC (OIFC, bk ), and
- an optical function symmetrical with respect to said meridian line in said given wearing conditions at least over a domain of gaze directions (a, b) joining the center of rotation of the eye of the wearer and the lens, where a is a lowering angle in degree and b is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in a = 8° and b = 0°
and where the optical power in the gaze direction corresponding to the fitting cross FC (OIFC, bk ) is greater than or equal to 5% of the prescribed addition.
2. The ophthalmic progressive addition lens according to claim 1, wherein
MaxSymPpo is smaller than or equal to 0.12*Add, with MaxSymPpo = max GapPpOj, with GapPpo, being defined for two gaze directions Ai and Bi, i=l,...,n
respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle bi, the different angles bi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapPpOj = ABS(Ppo(Aj)— Ppo(Bj)) with Ppo the optical power at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100 , the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
3. The ophthalmic progressive addition lens according to claim 1 or 2, wherein MaxSymAsr is smaller than or equal to 0.12* Add, with MaxSymAsr = max GapAsrj, with GapAsr, being defined for two gaze directions Ai and Bi, i=l,...,n respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle cu and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ to the meridian line, Ai and Bi being located on each side of the meridian line as GapAsr, = ABS(Asr(Aj)— Asr(Bj)) with Asr the unwanted astigmatism at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100 , the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
4. The ophthalmic progressive addition lens according to any of the preceding claims, wherein RMSSymPpo is smaller than or equal to 0.06*Add, with
RMSSymPpo = ~å GapPpo;2, with GapPpo, being defined for two gaze directions
Ai and Bi, respectively defines a couple of coordinate defined in the domain of gaze directions (a, b), having the same lowering angle ai and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapPpo; = ABS(Ppo(Aj)— Ppo(Bj)) with Ppo the optical power at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
5. The ophthalmic progressive addition lens according to any of the preceding claims, wherein RMSSymAsr is smaller than or equal to 0.06*Add, with
RMSSymAsr = ,with GapAsr, being defined for two gaze directions
Figure imgf000027_0001
Ai and Bi, respectively defines a couple of coordinate defined in the coordinate system (a, b), having the same lowering angle ai and having different azimuth angle Pi, the different angles Pi of Ai and Bi having an equal azimuth angular distance bΐ, relative to the meridian line, Ai and Bi being located on each side of the meridian line as GapAsrj = ABS(Asr(Aj)— Asr(Bj)) with Asr the unwanted astigmatism at each gaze direction in the given wearing conditions and n is the number of couple of gaze directions considered over the domain of gaze directions, n being greater than or equal to 100, the couples of gaze directions (Ai, Bi) being evenly distributed over the domain of gaze directions.
6. The ophthalmic progressive addition lens according to any of the preceding claims, wherein the module of unwanted astigmatism in the given wearing conditions is smaller than or equal to the prescribed addition of the wearer at least over said domain of gaze directions (a, b).
7. The ophthalmic progressive addition lens according to any of the preceding claims, wherein in the given wearing conditions the difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30.°
8. The ophthalmic progressive addition lens according to any of the preceding claims, wherein the given wearing conditions are standard wearing conditions.
9. The ophthalmic progressive addition lens according to any of the preceding claims, wherein the prescribed addition is greater than or equal to 0.5 Diopter and smaller than or equal to 5 Diopters.
10. A method, for example implemented by computer means, for determining an optical function of an ophthalmic progressive addition lens adapted for a wearer having a prescribed addition Add, comprising:
-obtaining an inset value, and
- determining in given wearing condition the optical function having • a meridian line with an inset corresponding to the obtained inset value and being symmetrical with respect to said meridian line in said given wearing conditions at least over a domain of gaze directions (a, b) joining the center of rotation of the eye of the wearer and the lens, where a is a lowering angle in degree and b is an azimuth angle in degree, the domain of gaze directions being a circle of radius greater than or equal to 36° and centered in a = 8° and b = 0°, and
• an optical power in the gaze direction corresponding to the fitting cross greater than or equal to 5% of the prescribed addition.
11. The method according to claim 10, wherein the optical function is determined so that the module of unwanted astigmatism in the given wearing conditions is smaller than or equal to the prescribed addition of the wearer at least over said domain of gaze directions (a, b).
12. The method according to claim 10 or 11, wherein the optical function is determined so as that is the given wearing conditions having a difference of lowering angle a between the fitting cross FC and the point of the meridian having an optical power corresponding to 85% of the prescribed addition Add is smaller than or equal to 30°, preferably smaller than or equal to 28°.
13. Method of obtaining an ophthalmic progressive addition lens adapted for a wearer having a prescribe addition Add, the method comprising the steps of the method of any of claims 10 to 12 and further comprises manufacturing an ophthalmic lens having the determined optical function.
14. A computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, causes the processor to carry out at least one of the steps of a method according to the invention.
15. A computer readable medium carrying one or more sequences of instructions of the computer program product according to the invention.
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