FR2536180A1 - OPHTHALMIC LENS WITH PROGRESSIVELY VARIABLE FOCAL POWER, DETERMINED IN ACCORDANCE WITH CONVERGENCE - Google Patents

Abstract

OPHTHALMIC LENS HAVING A PROGRESSIVELY VARIABLE FOCAL POWER, TAKING INTO ACCOUNT THE CONVERGENCE OF THE EYES, IN WHICH A QUANTITY OF A HORIZONTAL DISPLACEMENT H OF AN OMBILICAL MERIDIAN CURVE MM HAS A PROPORTIONAL RELATIONSHIP TO THE ADDITIONAL POWERS OF THE HORIZONTAL REPLACENT REFERENCE . APPLICATION TO THE CORRECTION OF PRESBYTIA.

Description

i 2536180

  This invention relates to persons

  Functions made to ophthalmic lenses to correct presbyopia and which have a progressively variable focal power and more particularly relates to an ophthalmic lens of the type described above in which the convergence of the eyes has been taken into consideration. Presbyopia refers to a state of a person's eyes such that the ocular lens in the eyeball can no longer accommodate a focus necessary for near vision because of the loss of its initial elasticity. can again easily see an object located a short distance from her when she will carry a convex lens that

  compensates for the lack of accommodation.

  It is usual for a near vision to be made by the lower zones of lenses mounted in a spectacle frame. Therefore, a single pair of spectacles can make the necessary visual power offsets for both near vision and vision when the lower zones of conventional lenses for remote viewing in the frame are replaced by convex lenses

described above.

  A bifocal lens is the most

  simple of an ophthalmic lens with several foci.

  The convex lens portion for near vision in the multi-focus ophthalmic lens is called the segment, and there are a variety of kinds of shape,

  location, substance, etc., of the segment.

  However, lenses of this kind have a common defect such that, during a vision shift from a distance vision to a near vision, there is a sharp change in image magnification of where

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  results in a feeling of physical confusion

  posed a so-called ophthalmic lens with progressive power, which is an ophthalmic lens having a power

  gradually varying, in an attempt to

  Variation of the abrupt change in image magnification According to the so-called progressive ophthalmic lens, the surface design of the lens is such that the refractive power varies gradually to eliminate the feeling of physical confusion felt during a vision shift between distance vision and near vision, and the intermediate field of view can also be provided in the region of the boundary between distance vision and

near vision.

  This progressive power lens is also

  aesthetically advantageous compared to the conventional bifocal lens in that the boundary line separating the lens portion for near vision of the part for remote viewing is not visibly perceived in the external appearance conne with the lens bifocal, and so it is not perceived as

  being prepared specifically for presbyopia.

  The ophthalmic lens with progressive power is characterized by the presence of a succession of "umbilics" forming what is called an "umbilical meridian curve" extending essentially from a

  upper central part to a lower central part

  of the lens surface. This "merit curve"

  "umbilical dien" is such that the astigmatism along it is almost equal to zero, and that the power

  refraction varies gradually according to a specific rule

  The term "umbilical" is used here to refer to the point where two main radii of curvature are

equal to each other.

  This main curvature radius is a mathematical term used to express the property of a curved surface and has the meaning that is going to be

described here.

  In FIG. 1, the symbol S designates a curved surface and P designates a point on this curved surface S The symbol Z designates a line normal to the point P on the curved surface S, that is to say a straight line passing through the point P and penetrating at right angles into the curved surface S at this point P. When a plane containing this normal ú intersects the curved surface S, it defines between them a curve called "secant curve" and there is an infinite number of these intersecting curves passing through the point P Gold, among the radii of curvature of each of these secant curves passing through the point P, the maximum and minimum radii are described as "two principal radii of curvature" at the point P When these two radii of As a consequence, a spherical surface is the only curved surface of which each of the points constitutes the "umbilicus" and, in this case, any curve of the curved surface

  produces the "umbilical meridian curve" described below.

above.

  When the point P is the umbilical ", we consider

  the part of the surface adjacent to this point P is practically spherical, and it can be said that at this point P the astigmatism is equal to zero. The term "astigmatism" is used here to denote the difference between the two rays. of the principal curvature specified above when these are replaced by the refractive powers The radius of curvature can be converted into the refractive power (whose unity is the diopter) by the following equation universally known in this field of the art:

D = N 1

D = R

  R a: - o D is the refractive power whose unit is the diopter, R is the radius of curvature whose unit is the meter, and N is the refractive index of the

lens, which has no unity.

  It follows from the explanation above that the "umbilical meridian curve" extends substantially from an upper central portion to a lower central portion of the surface of the ophthalmic lens.

progressive power.

  Astigmatism along this "merit curve"

  The umbilical cord is almost equal to zero, as already indicated, and the "umbilical meridian curve" has the most advantageous optical properties.

  on the surface of an ophthalmic lens with

  Thus, it is quite natural that the "umbilical meridian curve" be arranged at the position corresponding to the frequency of use

-the highest.

  The main purpose of the present invention

  is to provide a new ophthalmic lens

  Factored having a progressively variable focal power in which the amount of displacement or horizontal shift of the "umbilical meridian curve" has a proportional relationship to the refractive power

  additional to the respective positions of the horizontal

  zontal. Other features and benefits of

  the invention will emerge from the description which follows,

  which, of course, has no limiting character, with reference to the various figures of the appended drawing, in which Figure 1 is a schematic view illustrating "the umbilicus" and the main radii of curvature at this point; FIG. 2 is a schematic view showing the relative positions of a visual target, eyeballs and an ophthalmic lens, to illustrate the desired disposition of the "umbilical meridian curve" on the surface of this lens and the distribution of additional refractive power, and FIGS. 3 (A) and 3 (B) are respectively an elevational view of an embodiment of the ophthalmic lens according to the present invention, and a schematic view showing the arrangement of the "umbilical meridian curve" and the distribution of additional refractive power in accordance with

the present invention.

  In order to find the desired arrangement of the "umbilical meridian curve" on the surface of an ophthalmic lens, we will now consider the case in which this "umbilical meridian curve" coincides with the place of the movement of the lines of fixation on the surface of the lens, when the wearer of the glasses gradually turns his eyes towards a close visual target arranged: in front of him, at a slightly lower position after looking at an object located; in front of him, at an infinitely distant position The convergence of the eyes defines the concentration function of the lines of fixation of the eyes towards the

  target in the case of binocular vision.

  In FIG. 2, the symbols OR and OL respectively designate the centers of rotation of the globes of the right eye and the left eye, the symbols CR and CL respectively designate the vertices of the corners of the right eye and the eye. left and the symbol I denotes an infinitely distant point in front of the

  wearing glasses (because of the limited space

  available, only the direction of this point I has been

indicated by an arrow).

  The symbol T designates the position of a visual target disposed at a finite distance in front of the wearer of

  glasses in the case of binocular vision; P

  defining the point of intersection between the TOR line and the surface of the lens, where F is the foot of a high perpendicular from point P to the right IOR, and G is the foot of a high perpendicular from point T to the right OLOR Since the lines IOR and TG are parallel to each other, the angle GTOR is equal to the angle PORF These two angles are designated by O 'If now, the right eye is turned from the state of vision of the visual target T to the state of vision of the

  point I, the line of: attachment of the eye-right moves from one dis-

  PF on the surface of the lens because of the

convergence of the eyes.

  The power of accomnodation of the eyeball, the refracting power of the lens for far vision and the additional refractive power of the lens at the point P on the surface of the lens are respectively defined by De, Df and Dp under these conditions. since the distance between the eyeball of the right eye and the visual target T is TCR, Dp must be: Dp = Df + -De (1)

T

  R (The unity of the refractive power is the diopter and the unit of distance is the meter It is the same with regard to all the expressions which follow)

R PF

In addition, sin O = = -

TCR + CROR POR

R R R -

  and the TCR relationship "CRO Rest generally valid.

  As a result, the expression defining sin O

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  can be replaced by the following approximation: ORG p

TCR POR

R 2 F

  R Po Consequently, the increment of power D at the point P is expressed by: 1 i PF

D = DD Df = D From D (2).

TCR ORG X POR

  From expression (2), PF is obtained by: PF = ORG x x D + ORG x PO x D (3) RG XPR + R R e

  In equation (3), ORG, POR and De can be considered

  As practically constant We write for PF, PF = H, A being a constant of proportionality and B a constant With these conventions, equation (3) can be written:

H A x D + B (4).

  In order to obtain the optimal layout of the said

  "umbilical meridian curve" and the optimal distribution

  Male of additional refractive power, he is extr 4-

  it is desirable that the following relation be satisfied: H + A x D + B. where D is the additional focal power along the "umbilical meridian curve", where H is the amount of displacement or shift towards the nasal side with respect to the part of the lens intended for distance vision, A is the proportionality constant

and B is the constant.

  Although the description above did not

  reference to the right eye, it is obvious that

  what has been said about it also applies to the left eye.

  FIG. 3 and Table 1 represent an embodiment of a compliant ophthalmic lens

to the present invention.

  Referring to Fig. 3 (A), the symbol Q denotes a lens for the right eye seen from its convex face, O decodes the geometric center of the lens Q, LL 'denotes a meridian curve passing through the point O, MM 'denotes a meridian-umbilical curve passing through the point Q and N denotes a point producing a maximum additional refractive power on the umbilical meridian curve MM' An axis

  Coordinate H (which represents the amount of displacement

  horizontally, which corresponds to the distance PF in the figure, 2) extends horizontally to the right from the origin 0, while a coordinate axis V (which represents the vertical displacement) descends vertically from the The coordinates H and V of the point N have the values H max and V max respectively. The curve of Figure 3 (E) shows how the additional refractive power D varies along the umbilical meridian curve MM 'A coordinate axis D (representing the additional refractive power) extends horizontally to the right from an origin O 'corresponding to the origin O of FIG. 3 (A),

  while an axis of coordinate V (representing the

  vertical placement) extends vertically downward from

  of the origin O 'The coordinate D of a point N' corres-

  at point N of Figure 3 (A) has a D max value This Dmax is commonly referred to as "the addition" and has been

  set at 1.00 diopters in the present embodiment.

  Table 1 below shows the values

  coordinates D and H on the umbilicus meridian curve

  licaj e M-M ', which correspond to the values of the coordon-

  V measured at intervals of 2 mm, when the values of V and H are: V = 12.0 mm and max max max

Hmax = 2.5 mm.

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Table 1

  Coordinate V: 2: 4: 6: 8: 10: 12 Coordinate D: 0.07: 0.25: 0.50: 0.75-: 0, 93: 1.00 Coordinate H: 0.2: 0, 6: 1,3: 1,9: 2,3: 2,5 It is clear from Table 1 that the values of A and B in the above expression H 4 A x D + B are chosen so that we have A = 2.5 and B = 0.0 in the embodiment of this

invention.

  The lens for the left eye is symmetrical or is the specular image of that for the eye

  In other words, their configurations of surface area

  úringente 'are the same in the vertical direction and

  are ntriques from each other in the horizontal direction.

  In the embodiment above

  the present invention, it is applied to the

  appears from the umbilical meridian curve MM 'on which the distribution of additional refractive power ranges from the value 0, 0 to the "addition" which is 1.0. However, the present invention can be applied to a part of the curve Umbilical meridian MM 'o the additional refractive power varies up to at least 80% or more of the addition Accordingly, an ophthalmic lens in which the present invention is applied to the part of the umbilical meridian curve MM' on which the power additional refraction varies up to at least% or more of the power addition limit, also enters the box and in the range

  claims of the present invention.

  The terms "umbilicus" and "umbilical meridian curve" used in this specification are mere mathematical definitions in the strict sense, and it is true that such a point and such a curve can not be fully produced at the time of writing. surface of an ophthalmic lens that is a product of industry As a result, a meridian curve on which an astigmatism not exceeding 0.25 diopters may occur as a result of unavoidable errors

  such as manufacturing and instrument errors

  tation, corresponds to the "umbilical meridian curve" thus qualified in the present invention and an ophthalmic lens having such a "meridian curve"

  umbilical "also falls within the scope of the

  of the present invention.

Claims (3)

lREVENDICATIONS   Ophthalmic lens with progressively variable focal power, taking into account the convergence of the eyes, characterized in that the amount of a horizontal displacement of an umbilical meridian curve has a relationship proportional to an additional refractive power at the respective positions of said horizontal displacement.   2 Ophthalmic lens according to the claim   1, characterized in that one of the two refractive surfaces of said lens (Q) contains a first imaginary meridian curve (MM ') defined as an "umbilical meridian curve" extending substantially in the vertical direction along the refractive surface when said refracting surface is viewed in a direction substantially orthogonal to it, in the case where said lens is in the same vertical direction as when mounted on a person wearing it, a set of main radii of curvature at any of the points on said umbilical meridian curve (M-M ') being substantially equal to one another so that the astigmatism along said umbilical meridian curve (M-M') on said refracting surface is   almost equal to zero, the distribution of refractive power   along said umbilical meridian curve (M-M ') on said refracting surface including an area in which the refractive power increases progressively from an upper part to a lower part of said curve according to a predetermined law in which the refractive power varies in a non-uniform manner, said umbilical meridian curve (M-M ') dividing said refractive surface into two lateral zones respectively closer to the nasal side and the temporal side when said lens is mounted on the person wearing it, said refractive surface being such as when one imagines a second meridian curve extending in the vertical direction along said refractive surface so as to cover, cut or be osculative to said umbilical meridian curve in an upper region of said refracting surface, said curve umbilical meridian (M-M ') is shifted to the nasal side by rap port to said second meridian curve (L-L ') in a lower region of said refracting surface, while it is progressively less displaced towards the nasal side with respect to said   second meridian curve (L-L ') in an international region   intermediate of said refractive surface, and in that said umbilical meridian curve (M-M ') is such   that in a part of the said meridian curve ombi-   where the additional refractive power varies up to 80% or more of a predetermined addition provided for said lens, the relationship H A x D + B   is substantially satisfied, where D is the refractive power   additional gent-at a point on said umbilical meridian curve (M-M '), H is the displacement of said point from said second meridian curve, A is a proportionality constant and B is a constant.   3 Ophthalmic lens according to the claim   1, characterized in that the astigmatism along   of said umbilical meridian curve (M-M ') is greater than   zero but not more than 0.25 diopters.