FR2676551A1 - Lens for presbyopia having neither short-distance nor intermediate-distance aberration - Google Patents

Abstract

The present invention relates to a lens for presbyopia having a front face of a smaller radius of curvature than its rear face, and which does not exhibit any aberration at short distance or intermediate distance. According to the invention, the front face (11F) of the lens (11) has an index of refraction which is corrected in succession as the face of the lens moves away radially outward from the geometric center (12) of the lens. lens so that the lateral magnifications for all major rays are always equal to the lateral magnifications for paraxial extent. The invention applies in particular to the correction of presbyopia.

Description

This invention relates to a lens for presbyopia not having

  no short-range or intermediate-distance aberrations for use in correcting the vision of an elderly person In the presbyopic lens having a lens or front lens face of a smaller radius of curvature than a face of rear lens, the face of the lens has its refractive index which is corrected in succession while the lens face extends radially outwardly away from the geometric center of the lens so that the lateral magnifications for all rays are always equal to lateral magnification for a paraxial extent This construction is totally free of distortion aberration and

  provides a greatly enlarged range of distinct vision.

  When presbyopia develops while the lens in the eyeball has a diminishing power of adjustment, the accommodation to see a close object becomes impossible Generally, in this case, glasses with glasses can be used

  convex to compensate for the power of adjustment.

  An example of convex glasses known for presbyopia is shown in FIG. 5. It is a glass 50 for presbyopia having a front face 50 F whose radius of curvature r (1) is smaller than the radius of curvature r (2) of the rear face 50 R. More particularly, taking a glass of two degrees of diopter, for example, the smallest radius of curvature r (l) is set to 116.754 mm and the largest

  radius of curvature r (2) to 218.667 mm.

  In the known glass shown for presbyopia, the radii of curvature r (1) and r (2) above are both fixed radially outwardly of a geometrical center 51 of the glass 50. Therefore, the ratio of the size (lateral magnification) between an object and a virtual image seen through the lens 50 varies with the position of the object, which results in a distortion aberration This phenomenon is all the more remarkable as the degree of the lens or glass is

higher.

  Moreover, as shown in hatching in FIG. 5, conventional glass 50 offers a narrow range of distinct vision. For example, if the user wears glasses of two degrees, a close point corrected on an optical axis a is at a distance of 300 mm (which is the distance from the diaphragm of the eyeball 52) and a corrected distant point is at a distance of 504 mm (the focal length of the lens) assuming that the far point is at infinity in looking in the user's naked eye The distinct range of vision is narrow with the near point at 300 mm and the distant point at 504 mm also when the direction in which the eye looks forms an angle of 01 or G 2 of 30 degrees with the optical axis a This phenomenon is all the more remarkable as the degree of the lens is

higher.

  Thus, when the lens or lens 50 of a conventional construction is used, the distinct range of vision is limited to short distances and

  the image is distorted by distortion aberration.

  This results in the disadvantages that the eyes are tired after a long period

  of use in the absence of a comfortable visual sense.

  The main object of the present invention is to provide a lens for presbyopia, which does not exhibit short-range or intermediate-distance aberration, which does not involve any distortion aberrations and which makes it possible to obtain a strongly

increased distinct vision.

  Another object of the present invention is to provide a lens for presbyopia which does not exhibit aberration at short range or intermediate distance and which, when used, does not involve any deformation of an object and which makes it possible to get a comfortable visual sense causing little fatigue of

  the eye after a long period of use.

  The invention will be better understood and other purposes, features, details and advantages thereof

  will appear more clearly during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given solely by way of example illustrating an embodiment of the invention and in which: FIG. 1 is an explanatory view of a lens for presbyopia not presenting short-range aberration or intermediate distance according to the present invention; Figure 2 is an explanatory view showing the state of the front face of the lens before correction; Fig. 3 is an explanatory view showing the state of the front face of the lens after correction; Figure 4 is an explanatory view showing the distinct range of vision of the lens according to the invention; and Fig. 5 is an explanatory view showing the distinct range of vision of a conventional lens. A lens with a front face having a corrected refractive index will be described in detail according to one embodiment of this invention with reference to

at drawings.

  The drawings show a lens for presbyopia, showing no aberration at short distance or intermediate distance In FIG. 1, a lens 11 for presbyopia defines a front face 11 F having a radius of curvature smaller than the radius of curvature r (2) of its rear face 11 R The radius of curvature r '(l) of the front face 11 F of the lens 11 is corrected in succession while the front face extends radially outwardly away from a geometric center of the lens 11 so that the radius of curvature r '(1) increases progressively to have a lateral magnification for all major rays which is equal to the lateral magnification for a paraxial extent. Figures 1 and 2 show in phantom tracing the radius of curvature r (l) before correction Figures 1 and 3 show in full line the radius of curvature r '(l) after correction The radius of curvature r (l) is corrected whereby the radius of curvature r '(1) is progressively larger than the radius of curvature r (1) while the front face 11 F of the lens 11 moves radially outwardly from the center

geometric 12 of the lens.

  A specific construction of the lens it for presbyopia will be described below, taking as

  example a lens of two degrees.

  When the lens 11 is used as shown in FIG. 1, the distance E'P 'on an optical axis a between the front face of the diaphragm of an eyeball 13 and the rear face R11 of the lens 11 and set to 18 mm , the lens 11 has a thickness d (l) on the optical axis set at 3 mm, the distance d (O) on the optical axis a between the front face of the lens wire 11 and an object 14 is 300 mm, the radius of curvature r (2) of the rear face 11 R of the lens 11 is 218.667 mm and the radius of curvature r (l) of the front face of the lens 11 is 116.754 mm magnification The lateral value for a paraxial extent is 2.44136 which is derived from the refractive index of air N '(O) which is 1 and the refractive index N' (1) of the lens 11. formed of a transparent acrylic resin which is 1.492 The distance on the optical axis a between the rear face 11 R of the lens 11 and a virtual image 15 is

-731.11 mm.

  When the height y (0) of the object 14 is 10 mm, the radius of curvature r '(1) of the front face 11 F which is 116.754 mm is corrected to be 116.8539962768555 mm so that the virtual image 15 has a height y '(3) equal to the lateral magnification above f, so that the virtual image 15 having a height y (3) before correction is changed for a height y' (3) which is 24,413 mm So the

  lateral magnification is y '(3) / y (O) = 2.44134.

  Indeed, the radius of curvature of the front face F11 of the lens 11 is increased by r (1) to r '(1), so the horizontal length x (1) and the vertical length y (1) of the coordinates of a point of intersection between a main radius and the curved face as shown in Figure 2 are corrected to be a horizontal length x '(1) and a vertical length y' (1) of coordinates of the point of intersection between the radius main and curved side. Then, when the height y (0) of the object 14 is 20 mm, the radius of curvature r '(1) of the front face 11 F is corrected to be 116.9539947509766 mm so that the virtual image 15 has a height y '(3) equal to the lateral magnification above, and the virtual image 15 having a height y (3) before correction is changed for a height y' (3) which is 48.44166 mm , the lateral magnification is

y '(3) / y (O) = 2.44166.

  Then, when the height y (O) of the object 14 is 30 mm, the radius of curvature r '(1) of the front face 11 F is corrected to be 117, 453987121582 mm so that the virtual image 15 has a height y '(3) equal to the lateral magnification (above, and the virtual image 15 having the height y (3) before correction is changed to a height y' (3) which is 73.24796 mm Then, the lateral magnification a is y '(3) / y (O) = 2.4416 Then, the height y (0) of the object 14 is increased in succession of 10 mm, and the radius of curvature r (1) of the front face 11 F is increased as described

  above until y (0) equals 170 mm.

  Only numeric values will be given by the

speed of explanation.

  When y (O) is 40 mm, r '(1) = 118.1539764404297 mm' (3) = 97.6602 mm, and

C, 2.4415.

  When y (O) is 50 mm, r '(1) = 118.9539642333984 mm, y' (3) = 122.077 mm, and

δ = 2.44154.

  When y (O) is 60 mm, r '(1) = 120.0539474487305 mm, y' (3) = 146.481 mm and

8 = 2.44136.

  When y (O) is 70 mm, r '(1) = 121.1539306640625 mm, y' (3) = 170.903 mm and

= 2.44147.

  When y (O) is 80 mm, r '(1) = 122.5539093017578 mm, y' (3) = 195.306 mm, and

= 2.44133.

  When y (0) is 90 mm, r '(1) = 123.9538879394531 mm, y' (3) = 219.731 mm, and

r = 2.44145.

  When y (O) is Omm, r '(1) = 125.6538619995117 mm, y' (3) = 244.129 mm, and

6 = 2.44129.

  When y (O) is 11 Omm, r '(1) = 127.3538360595703 mm, y' (3) = 268.551 mm, and

I = 2.44137.

  When y (O) is 120 mm, r '(1) = 129.25390625 mm, y' (3) = 292.957 mm, and

e = 2.44131.

  When y (O) is 130 mm, r '(1) = 131.1540222167969 mm, y' (3) = 317.386 mm, and

e = 2.44143.

  When y (O) is 140 mm, r '(1) = 133.254150390325 mm, y' (3) = 341.793 mm, and

e = 2.44138.

  When y (O) is 150 mm, r '(1) = 135.4542846679687 mm, y' (3) = 366.194 mm, and

e = 2.4413.

  When y (O) is 160 mm, r '(1) = 137.6544189453125 mm, y' (3) = 390.615 mm, and

8 = 2.44134.

  When y (O) is 170 mm, r '(1) = 139.9545593261719 mm, y' (3) = 415.024 mm, and

8 = 2.44132.

  In this way, the radius of curvature r '(1) of the front face F11 of the lens 11 is increased in succession so that the lateral magnifications for all the principal rays are equal to the lateral magnification 3 for the paraxial extent. F 1 l front face of the lens has a unique and aspherical structure, the distortion aberration is completely eliminated to give the effect allowing

  make a lens free of aberration.

  In addition, a greatly increased range of distinct vision is provided, as shown by the hatching of FIG. 4 Taking for example the lens 11 of two degrees, the near point on the optical axis a is at 300 mm and the distant point at 504 mm In the state where the principal rays b form an angle -1 or e 2 of 30 degrees with the optical axis a, the distinct range of vision is greatly increased with the near point at about 373 mm and the point distant to about 780 mm This effect is all the more remarkable as the degree of

lens is higher.

  Thus, when using the lens 11 of the above construction, there is no fluctuation of the image due to the movement of the eyeball and a sharp field of vision is assured, which covers a short distance to an intermediate distance Thus, a comfortable visual field is assured and fatigue of the eye

  resulting from a long period of use is reduced.

  Moreover, as described above, since the radius of curvature of the front face F 1 1 of the lens increases progressively (i.e. the refractive index of the lens becomes gradually reduced), the front face F 1 l exceeds only a small amount, that is to say it has a small bulge The lens can be thinned the corresponding amount, which gives the effect of ensure a clearer field of vision and allow the lens to be

lighter.

  In the embodiment above, the radius of curvature of the front face of the lens is increased in succession to successively decrease the refractive index of the lens. The correction is not limited to the front face of the lens but it can of course be done only on the back or

well to the front and back.

Claims (1)

R E V E N D I C A T I O N   Lens for presbyopia having a front face of a smaller radius of curvature than its rear face, of the type having no aberration at short distance or intermediate distance, characterized in that it comprises a lens face (11 F) of which the refractive index is corrected in succession while the lens face moves radially outward from its geometric center (12) so that the lateral magnifications for all main rays are always equal to the lateral magnification for a paraxial extent.