NL8300742A - EYE CORRECTION LENSES WITH A SLOWLY CHANGING FOCAL DISTANCE IN DETERMINING WHICH TAKES ACCOUNT OF EYE CONVERGENCE. - Google Patents

Description

* ... * N.0. 31675 1

Correction lens with a gradually changing focal length when determining the convergence of the eyes.

The invention relates to improvements of vision correction lenses for use in farsightedness, which lenses have a gradually changing focal length, and more particularly the invention relates to vision correction lenses of the above-described type, which take into account the convergence of the eyes.

Farsightedness is such a state of the human eyes that the lens in the eye cavity is no longer able to adjust itself enough to achieve focusing necessary for close vision, due to loss of its original elasticity. Therefore, when wearing a convex lens that overcomes this lack of adaptability, the subject in question will be able to easily see an object present at a short distance again.

It is common for close vision to use the lower portions of spectacle-mounted lenses. It is then also possible to obtain the necessary visual adjustments, both for near vision and for far vision, with a single pair of glasses, by replacing the lower parts of the conventional far vision lenses in the frame with the above-described convex lenses.

A double focus lens is the simplest form of such an eye correction lens for multi-focal eye defects. The convex lens portion for near vision is called the segment in the multi-focus lens, and these segments exist in various shapes and sizes, positions, material and the like.

However, the lenses of this type had in common the drawback that during the transition from far vision to near vision, an abrupt change in the image magnification occurs, resulting in a sense of physical confusion. A so-called progressive focal lens, that is, a lens with a gradually changing focal length, has already been proposed in an attempt to reduce this abrupt change in the magnification of the image. With this gradually changing focal length lens, the surface of the lens is designed to gradually vary the refractive power to eliminate the sense of physical confusion that occurs during the transition from far to near vision, and also an area with intermediate vision are obtained in the borderline between far and near vision.

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This gradually changing focal length lens is also ethically advantageous over the conventional dual focus lens because the boundary line separating the near vision lens portion from the far lens portion is not noticeable in the external appearance of the glasses , in contrast to the double-focus lens, so it is not noticeable that the lens is specially manufactured for farsightedness.

The lens with gradually changing focal length is characterized by the presence of a series of "ombilic points" which form a so-called "ombilic meridian curve" which extends substantially from the upper central part to a lower central part of the lens surface. This "ombilic meridian curve" is such that the astigmatism along this curve is substantially zero and the refractive power gradually varies according to predetermined rules The term "ombilic point" is used to denote a point in which two principal radii of curvature are equal.

The main radius of curvature is a mathematical term used to indicate a property of a curved surface and its meaning will become clear in the following.

In Figure 1, the symbol S denotes a curved surface and P denotes a point on this curved surface S. The symbol t indicates a perpendicular to the point P on the curved surface S, ie a straight line passes through point P and penetrates orthogonally the curved surface S into point P.

25 When a plane passes through this perpendicular & the curved surface S

then a curve is defined therein, a so-called intersection curve, and there is an infinite number of such intersection curves through the point P. The radii of curvature of each of these intersection curves through the point P become the maximum radius of curvature and the minimum radius of curvature referred to as the two principal radii of curvature of the point P. When these two principal radii of curvature are equal to each other, point P is called an "ombilic point". A spherical surface is therefore the only one of the curved surfaces where any point on the surface is ombilic point ", in which case any of the curves on the curved surface will form the" ombilic meridian curve "described above.

If the point P is an "omni-point", then the surface portion in the vicinity of this point P can be considered as substantially spherical, and the astigmatism at this point P can be assumed to be substantially zero. The term "astigmatic-8300742-3" used herein refers to the difference between the above two main curvature radii when they are replaced by the refractive powers. The radius of curvature can be converted into a refractive power (expressed in the unit of diopters) by the following for the expertly known equation: DN ^ where D is the refractive power expressed in diopters, R is the radius of curvature in meters, and N is the refractive index. of the lens, which is unitless.

It has been described above that the "ombilic meridian curve" extends substantially from an upper central portion to a lower central portion of the surface of a gradually changing focal length lens.

The astigmatism along this "ombilic meridian curve" is substantially equal to zero as already described and the "ombilic meridian curve" has the optically favorable property on the surface of the lens with gradually changing focal length. Thus, it will be understood that the "ombilic meridian curve" should be positioned where the lens is most commonly used.

The present invention has as its primary object to provide a new and improved eye correction lens with a gradually changing focal length, in which the degree of horizontal displacement of the "ombilic meridian curve" has a proportionality relationship with the additional refractive power at respective positions of the horizontal displacement.

This object, further features and advantages of the invention will become apparent from the following detailed description of the figures, which show preferred embodiments of the invention.

Figure 1 shows a schematic view illustrating the "ombilic point" and the principal radii of curvature of that point.

Figure 2 shows a schematic view of the relative positions of a visual target, the eyeball and a correction lens illustrating the desired configuration of the "ombilic meridian curve" on the surface of the correction lens and the distribution of the additional refractive power.

Figures 3A and 3B show views of an embodiment of the correction lens of the present invention and show the position of the "ombilic meridian curve" and the distribution of the additive 8300742 4, respectively.

I

-Tional refractive power according to the invention.

To find the desired configuration of the "ombilic meridian curve" on the surface of an eye correction lens, first consider the case where this "ombilic meridian curve" coincides with the locus of motion of the fixation lines on the lens surface as the wearer gradually twists his eyes to a visual target, which is close at a slightly lower position in front of him, seen from a state in which he perceives an object that is an infinite distance in front of him. The convergence of the eyes defines the concentration function of the fixation lines of the eye towards a visual target in the case of binocular vision.

In Figure 2, the rotation points of the eyeballs of the right and left eye are denoted by the symbols 0¾ and 0 ^, while 15 Cr and Cl denote the respective vertices at the corners of the right and left eye, respectively, while the symbol I indicates an infinitely distant point for the spectacle wearer. (Due to space limitations, the direction of such a point I is indicated by an arrow only.) 20 The symbol T represents the position of a visual target located at finite distance for the spectacle wearer in the case of binocular vision, P indicates a point of intersection between the line TOr and the lens surface, F indicates the base of a perpendicular from point P in the direction of the line IOr, and G indicates the base of 25 a perpendicular drawn from point T in the direction. of the line O ^ Or. Since the lines IOr and TG are parallel to each other, the angle L GTOr is equal to the angle ^ POrF. These angles are defined by Θ.

Now when the right eye is rotated from the state looking at the point I to the state looking at the visual target T, the fixation line of the right eye moves a distance PF across the lens surface due to the convergence of the eyes.

The adaptability of the eyeball, the refractive power of the distant lens and the additional refractive power of the lens at the point P on the lens surface are defined by De, Df and Dp, respectively. Because the distance between the eyeball of the right eye and the visual target T is equal to TCr, Dp must be equal to 8300742 5

Dp = Df + ^ - De (1) (The unit of refraction power is the diopter, and the unit of distance is the meter. The same applies to the following expressions.)

Furthermore, it applies

. ° Rg EF

S 11 "tcR + CR ° R" f0R

10 and moreover, the general relationship TCr CrOr applies. Therefore, the expression for sinO can be approximated by 0R0 pp TCr * POr 15 Therefore, the power increase D in the point P is expressed by D - Dp - Df - ^ - The 20 s ^ __ j) (2)

OrG x POr ue W

Starting from the equation (2), PF is determined by 25 EF - OrG x POr x D + OrG x P0R x De (3)

In equation (3), OrG, POr and De can be considered as nearly constant. Suppose PF is equal to PF = H, that A is a proportionality constant and B is a constant, then the equation (3) can be written as H * A x D + B (4)

Thus, in order to obtain the optimal arrangement of the aforementioned "ombiliekmeridi-35 curve" as well as the optimal distribution of the additional refractive power, it is highly desirable to maintain the following relationship

E * AxD + B

. 8300742 r 6 where D is the focal length increase along the "ombilic meridian curve", H is the amount of displacement toward the nose relative to the lens portion serving for far viewing, A is the proportionality constant, and B is the constant.

5 Although in the above description attention has only been paid to the right, the same statement also applies to the left eye.

Figure 3 and Table 1 show an embodiment of the ocular correction lens according to the invention.

10 In Figure 3A, the symbol Q denotes a lens for the right eye, seen against the convex surface, 0 denotes the geometric center of the lens Q, L-L 'denotes a meridian curve passing through the point 0, MM "indicates an ombilic meridian crest frame passing through the point 0, and N" lists at a point with a maximum additional refractive power on the ombilic meridian curve M-M ". An H coordinate axis (representing the value of the horizontal displacement corresponding to the distance B? In Figure 2) extends horizontally to the right from the origin 0, and a V coordinate axis (representing the vertical displacement represents) extends vertically downward from the origin 0. The H coordinate and V coordinate of the point N have the values Hmax e1 Vmax, respectively.

The graph of Figure 3B shows how the additional refractive power D varies along the ombilic meridian curve M-M '. A D coordinate axis (representing the additional refractive power) extends horizontally to the right from the origin 0 * corresponding to the origin 0 in Figure 3A, and the V coordinate axis (representing the vertical displacement) extends vertically downward from the origin 0 '. The D coordinate of a point N '30 corresponding to the point N in Figure 3A has a value Dmax.

This Dmax is commonly referred to as the additive and is set at 1.00 diopters in the present embodiment.

Table 1 below gives the values of the D coordinate and the H coordinate on the ombilic meridian curve M-M ', corresponding to the 35 values of the V coordinate measured at 2 mm intervals, when the values of Vmax and Hmax respectively are equal to vmax = 12 ° ° and Hmax = 2> 5 m 8300742 • f 7 w> 3-

Table 1 V-coiS-ir ^ .- t 2 4 6 8 10 12 D-coordinate 0.07 0.25 0.50 0.75 0.93 1.00 5 H coordinate 0.2 0.6 1, 3 1.9 1.3 2.5

It is clear from Table 1 that the values of A and B in the above expression H = A x D + B are selected as A * 2.5 and B * 0.0 in the illustrated embodiment of the invention.

10 The lens for the left eye is mirror symmetrically similar to the lens for the right eye. That is, the refraction surface configurations are the same in the vertical direction but mirror-symmetrical with each other in the horizontal direction.

In the above-described embodiment of the invention, the invention is applied to the whole of the ombilic meridian curve M-M 'on which the distribution of the additional refractive power ranges from the value 0.0 to the addition equal to 1.0. However, the invention can also be applied to a portion of the central meridian curve M-M 'on which the additional refractive power varies at least 80% or more of the addition. Therefore, also an eye corrector, in which the present invention is applied to a part of the ombilic meridian curve M-M ', of which part the additional refractive power varies of at least 80% or more of the limit value of the added power, falls within the scope of the invention. .

The terms "ombilic point" and "ombilic meridian curve" used in this description are only mathematical definitions in the strict sense, and it is of course true that such a point and such a curve cannot be exactly produced on the surface of an eye correction lens, because such a lens is simply an industrial product. Therefore, a meridian curve on which an axis tigmatism does not exceed 0.25 diopters due to inevitable manufacturing and instrumentation errors is considered! to fall within the scope of the invention and such a curve is considered to be corresponding to the "ombilic meridian curve" described above and an eye correction lens having such "ombilic meridian curve" is therefore within the scope of the invention.

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Claims (3)

1. Correction lens with a gradually varying focal length, taking into account the convergence of the eyes, characterized in that the degree of horizontal displacement of a central meridian curve has a proportionality relation to an additional refractive power on respective parts of the mentioned horizontal displacement. 1 ·· CONCLUSIONS. An eye correction lens according to claim 1, characterized in that one of two refraction surfaces of said lens comprises an imaginary first meridian curve defined as an "ombilic meridian curve" extending substantially in vertical direction along said refraction surface. when said refraction surface is viewed in a direction substantially orthogonal to the surface in the state where the lens is in the same vertical direction as when mounted in a frame, further a group of main curvature rays of arbitrary points on the central meridian curve, substantially equal to each other such that the astigmatism along said ombilic meridian curve in said refraction surface is substantially equal to zero, the distribution of the refractive power along said ombilic meridian curve in said refraction surface a zone includes in which the refractive power gradually then from an upper portion toward a lower portion of said curve according to predetermined rules, and wherein the refractive power varies in a non-uniform manner, which ombilic meridian curve divides said refractive surface into two lateral regions, respectively. located closer to and further away from the nose when the lens is mounted in a frame, the refraction surface being such that when a second meridian curve extends vertically along said refraction surface to form said ombilic meridian curve in an upper intersecting or touching region of the refraction surface at one or more points, said ombilicid meridian curve is moved towards the nose side with respect to said second meridian curve in a lower region of said refraction surface, while moving less gradually towards the nose side n relative to said second meridian curve in an intermediate region of the refraction surface, and wherein said ombilic meridian curve is such that in a portion of this ombilic meridian curve in which the additional refractive power is at least 80% or more of a predetermined addition 8300742 for said lens varies mainly with the relationship H - A x D + B where D is the additional refractive power of a point on the said orbilian meridian curve, H is the displacement of said point from the second meridian curve, A a proportionality constant, and B is a constant. An eye correction lens according to claim 1, characterized in that the astigmatism along said orbilic meridian curve is greater than 10 zero but not greater than 0.25 diopter. *********** é «8300742