Source: http://www.google.ca/patents/US6270220
Timestamp: 2013-05-19 08:14:08
Document Index: 513808795

Matched Legal Cases: ['art 28', 'art 30', 'arts 28', 'art 30', 'art 28', 'art 34', 'art 36', 'art 28', 'art 28', 'art 34', 'art 36', 'art 34', 'art 30', 'art 30']

Patent US6270220 - Multifocal lens - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Web History | Sign inAdvanced Patent SearchPatentsA multifocal lens having far and near vision zones is presented. The lens comprises a substrate in the form of a progressive addition lens and a modulation formed on a surface of the substrate. The substrate lens has far and near vision zones, selected in accordance with respective prescribed values...http://www.google.ca/patents/US6270220?utm_source=gb-gplus-sharePatent US6270220 - Multifocal lensPublication numberUS6270220 B1Publication typeGrantApplication number09/334,067Publication date7 Aug 2001Filing date16 Jun 1999Priority date18 Jun 1998Also published asEP0967509A2EP0967509A3EP0967509B1InventorsEliezer KerenOriginal AssigneeRotlex (1994) Ltd.Y.M.S. Investment Ltd.U.S. Classification351/159.42International ClassificationG02B3/10G02C7/02Cooperative ClassificationG02C7/063G02C2202/20G02C7/061G02B3/10G02C7/068European ClassificationG02C7/06P2G02C7/06P4G02C7/06PG02B3/10ReferencesPatent Citations (8)Referenced by (20)External LinksUSPTOUSPTO AssignmentEspacenetMultifocal lensUS 6270220 B1Abstract A multifocal lens having far and near vision zones is presented. The lens comprises a substrate in the form of a progressive addition lens and a modulation formed on a surface of the substrate. The substrate lens has far and near vision zones, selected in accordance with respective prescribed values of optical power required for the patient's eye at his distance and reading vision, and an intermediate transition region between the far and near vision zones. The modulation is of kind producing locally variable power addition such that the far and near vision zones of the multifocal lens are wider than the far and near vision zones of the substrate.
FIELD OF THE INVENTION The present invention relates generally to multifocal lenses, and in particular to multifocal lenses combining the properties of progressive addition lenses (PAL) and diffractive lenses.
BACKGROUND OF THE INVENTION Multifocal lenses are known and widely used, being prescribed for those requiring different dioptric powers for distance and reading vision. This condition is called �presbyopia�. It mostly appears when one gets older and age renders it difficult for the eye (if not impossible) to focus on near and distant objects. This condition may be relieved by prescribing one pair of lenses for distance vision and another for reading vision. A single pair of either bifocal or multifocal lenses can replace both of these pairs of lenses.
The most common multifocal lens is the so-called �progressive addition lens� or PAL. This lens has a far vision zone located at the top of the lens, and a near vision zone located at the bottom of the lens, the far and near vision zones being connected by an intermediate transition region. In this intermediate transition region, called �corridor�, focus changes continuously from the focus at the far vision zone to that of the near vision zone. The locations of the far and near vision zones are dictated by the prescribed parameters of the optical powers required for an individual's �distance� and �reading� visions which define the lens' addition. Thus, a PAL is characterized by the gradual change of its optical power from the top of the lens to the bottom.
PALs are generally of two designs, so-called �hard� and �soft� designs, depending on the distance between the far and near vision zones, i.e., the length of the corridor, which ranges typically between 16 and 24 mm. The �hard� design is characterized by a relatively sharp transition region, as compared to that of the �soft� design. Such a sharp transition region induces large distortions on either side of the corridor. The �soft� design sacrifices the widths of far and near vision zones in favor of a more gradual transition with less distortion. The main principles of PALs of �hard� and �soft� designs are illustrated in FIGS. 1 and 2, respectively.
FIG. 1 shows an image I1 of a pattern of equidistant, vertical lines L, which is obtained through a PAL with �hard� power variations. It is evident, that the optical power at a bottom region RB of the lens, i.e. in the near vision zone which produces a relatively larger magnification for the reading vision, is larger than the power at a top region RT which is used for distance vision. Additionally, the line separation ΔLB in the bottom region RB is wider than the line separation ΔLT in the top region RT. With a progressive continuous power profile, top portions LT of the imaged lines L join smoothly with bottom portions LB, so that they must bend in the intermediate region, or corridor, of the lens. However, the line bending effect produces image distortion, for example, similar to that one would observe through a cylindrical lens with an axis at 45�. As shown, the distortion is minimal along the central vertical line L0, and increases towards periphery regions at both sides of the central vertical line L0. The width of the intermediate region between the far and near vision zones of the lens is determined by an area in the lens where distortion remains below a predefined threshold, normally 0.5 diopter cylinder. Thus, in the PAL of the �hard� design, the corridor is both short and narrow.
FIG. 2 illustrates an image I2 of a pattern of equidistant, vertical lines L, which is obtained through a PAL of a �soft� design with much more gradual progression. It is seen that the line bending is less pronounced here, as compared to that of the hard PAL shown in FIG. 1. Moreover, the distortion is lower, and a corridor is longer and wider. The height of a near vision zone, through which a lower region RB of the image I2 is obtained, and which is defined by the region where line-portions LB are straight and equidistant, is nevertheless much shorter. The same may be said about a far vision zone through which the upper region RT of the image I2 is obtained.
Diffractive lenses, in general, employ a different effect, as compared to the refractive lenses. Diffraction is a phenomenon that occurs when an electromagnetic wave, such as light, encounters an obstacle and propagates non-linearly. This ability to �bend� a part of a light beam is the basic property used to realize any diffractive lens. Diffractive lenses are lightweight substitutes for the conventional refractive lenses used in monochromatic applications.
FIG. 4 illustrates a profile 10 of a phase grating utilizing the Fresnel zone plate. For example, the profile 10 is designed such that a single diffraction order, for example �−1�, survives. It is understood that with the grating pitch becoming smaller with the radial distance, the diffraction angle, or beam bending effect, grows proportionally, and an incident collimated light beam becomes focused on a point, which is the typical behavior of a lens. This is the physical principle on which the diffractive contact lens relies to achieve its aim.
SUMMARY OF THE INVENTION There is accordingly a need in the art to improve multifocal lenses by providing a novel multifocal lens that combines the advantages of PAL with those of diffractive lenses.
FIG. 1 schematically illustrates an image of a pattern of equidistant, vertical lines, observed through a PAL with �hard� power variation;
FIG. 2 schematically illustrates an image of a pattern of equidistant, vertical lines observed though a PAL with �soft� power variation;
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FIGS. 1 and 2 schematically illustrate the main principles of PALs with �hard� and �soft� power variations, respectively. FIGS. 3 and 4 illustrate, respectively, the Fresnel zone plate and a diffraction grating utilizing the same. FIG. 5 illustrates the tri-focal diffractive lens.
In the present example, the diffraction grating 26 is a phase grating producing three diffraction orders, for example, �−1�, �0� and �+1�. A grating period distribution of the diffraction grating 26 is carefully designed such that the power of the grating 26 vanishes at a top part 28 and a lower part 30 of the PAL substrate 24. An intermediate transition region 32, or corridor, is located between the top and the lower parts 28 and 30 of the PAL substrate 24.
It should be noted that the PAL substrate 24 could be of a �hard� design. Additionally, although not specifically shown, the modulation 26 could be formed on a concave surface of the substrate 24.
The main operational principles of the lens 22 will now be described with reference to FIG. 7. Three graphs, G1, G2 and G3, illustrate the power distribution of the lens 22 while focusing, respectively, three diffraction orders �+1�, �0� and �−1�(positive, zero and negative orders) along the lens between the far and near vision zones 28 and 30. Each graph presents the dependence of the dioptric power of the lens 22 (X-axis) in the intermediate region 32 with the position along the height of this region (Y-axis). It should be understood that the illustration in FIG. 7 is qualitative and is therefore not drawn to any specific scale. For example, the full scale along the Y-axis may be 40 mm.
The range of the positions along the height of the corridor 32 starts from the origin Y1 which borders with the lower part 30, and continues up to the edges of the top part 28, i.e., the coordinate Y2. Graphs G1, G2 and G3 look like S-shaped hysteresis curves rotated by 90� to vertical position, with all three curves converging together and joining in a left upper part 34 and right lower part 36 of FIG. 7.
The zero order (graph G2) does not deflect light beyond the normal refraction of the lens material, but rather behaves like the original �soft� design PAL substrate 24. As indicated above, the power of the grating vanishes at the top part 28 of the PAL substrate 24 such that the diffractive power of the grating 26 there is equal to zero, and, as seen in FIG. 7, the three orders are identical. Hence, when the wearer of the multifocal lens 22 looks through the far vision zone 28, where there is zero power addition produced by the grating, he enjoys the advantage of all the light available.
Now moving downward from the top part 28 of the PAL substrate 24 into the corridor 32, by moving from the left upper part 34 to the right lower part 36 of FIG. 7, it is seen that the three orders begin to separate. This is due to the changes in the diffraction power of the grating. At the left upper part 34, where the zero order (central curve G2) starts to bend, the �−1� order (curve G3) is still constant.
The effect on the far vision zone 28 is shown in FIG. 8, which illustrates an image IMT of upper portions LT of equidistant vertical lines L observed through the far vision zone 28 of the lens 22. As shown, focusing on the �−1� order, has the effect of increasing the far vision zone 28 with a major part of the transition region 32, and without sacrificing the transition region.
Since the power of the grating vanishes at the bottom part 30 of the PAL substrate 24, as shown in FIG. 7, the three orders are identical, thereby causing the multifocal lens 22 to behave like the original �soft� design PAL substrate 24. Subsequently, when descending along the �+1� order (curve G1) towards the lower part 30 of the PAL substrate 24, which is intended for near vision, the diffraction grating 26 increases the near vision zone 30 by adding a major part of the corridor 32 to the near vision zone 30.
The modulation of the surface of the lens 22 producing a phase grating is more pronounced in the transition region 32, where it brings about a separation between the three orders �−1�, �0� and �+1�, as shown in FIG. 7. It should be noted that the diffraction effect diminishes towards the edges 28 and 30, where the multifocal lens 22 behaves like an ordinary PAL.
The advantages of the present invention are self-evident. Indeed, all three diffraction orders exhibit soft low distortion profiles. The lens is characterized by relatively wide far and near vision zones, as compared to those of a conventional PAL. All the light energy is available over the sizable portion of both the far and near vision zones. Diffraction haze (image blurring) occurs only along the transition zone (corridor), and is less prominent, as compared to pure diffraction lenses. This is due to the fact that the power differential between the different diffraction orders is smaller. The diffraction grating parameters on either side of the corridor can vary towards the reduction of the distortion that remains there even with a �soft� profile. The change of the power of the diffraction grating with the light wavelength compensates for the change induced by the refractive power of the PAL substrate, thereby reducing the chromatic aberration of the entire combination.
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