TECHNICAL FIELD
[1] The present invention relates to multifocal diffractive lenses mainly used for intraocular
lenses.
BACKGROUND
[2] Conventional multifocal diffractive lenses are often configured to focus 0-order light
(refracted light) at a focal point for far vision and focus +1-order light (diffracted light) at
a focal point for near vision or intermediate vision. As an example of multifocal
diffractive lenses of different types from the above, a multifocal ophthalmic lens is
disclosed which is configured to focus +1-order light (diffracted light) at a focal point for
far vision to reduce the chroma aberration (refer to patent literature 1). As another
example of multifocal diffractive lenses, a trifocal lens is disclosed which is configured to
focus 0-order light (refracted light) at a focal point for intermediate vision, focus +1-order
light (diffracted light) at a focal point for near vision, and focus -1-order light (diffracted
light) at a focal point for far vision (refer to patent literature 2). Further, an ophthalmic
lens is disclosed which has negative diffractive power to increase the range of chroma
aberration (refer to patent literature 3).
[3] ISO 11979-2, which relates to test methods for optical properties of intraocular lenses,
prescribes that the refractive power, the modular transfer function (MTF), and the like
should be measured with monochromatic light sources of wavelengths of 546±10 nm.
Specifications of intraocular lenses are determined based on these monochromatic
performance evaluations. Here, as understood from the fact that the chroma aberration is
discussed in patent literature 1, attention has been paid to polychromatic (white)
performance evaluation of multifocal lenses. The multifocal lens of patent literature 1
does not however take account of misalignment between the focal position for
monochromatic performance and the focal position for polychromatic performance, and
commonly-used optical designing of intraocular lenses based on the monochromatic
performance at a wavelength of 546±10 nm in accordance with ISO 11979-2 causes a
shift of the focal position between the monochromatic performance and the polychromatic
performance. A conventional multifocal diffractive lens is often such that the focal
position for far vision in polychromatic performance evaluation is located farther from the
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multifocal diffractive lens than the focal position for far vision in monochromatic
performance evaluation. In this case, light allocated to far vision is focused on the retina
and behind the retina. This may prevent efficient use of light, causing mismatching of
actual performances from the intraocular lens specification.
PRIOR ART LITERATURES
[4]
[Patent Literature 1] International Publication No. 2018/100459 A1
Patent Literatures
[Patent Literature 2] International Publication No. 2019/020435 A1
[Patent Literature 3] JP S59-224818 A
SUMMARY OF INVENTION
[5] The present invention has been made in view of the problem discussed in the abovedescribed Background, and an objective of the present invention is to provide a multifocal
diffractive lens which allows efficient use of light.
[6] To achieve the above-described objective, a multifocal diffractive lens according to the
present invention includes a diffraction grating. Negative-order light produces a focal
point for far vision while 0-order light produces a focal point nearer to the multifocal
diffractive lens than that of the far vision. The number of focal points is two or more. A
focal position for far vision in polychromatic performance evaluation is located nearer to
the multifocal diffractive lens than the focal position for the far vision in monochromatic
performance evaluation.
[7] Since the above-described multifocal diffractive lens is configured as a multifocal lens
that causes the focal point for far vision in polychromatic performance evaluation to be
located nearer to the lens than the focal point for far vision in monochromatic
performance evaluation, the focal point for far vision is located nearer to the intraocular
lens (the multifocal diffractive lens) than the retina in the visual light range, which makes
it possible to bring an object at a finite position into focus, allowing efficient use of light.
[8] In a specific aspect of the present invention, the above-described multifocal diffractive
lens causes positive-order light to further generate a focal point nearer to the multifocal
diffractive lens than that of 0-order light and the number of focal points is three or more.
In this case, it is possible to achieve image formation for three or more target distances.
[9] In another aspect of the present invention, the diffraction grating is in a combined shape of
kinoform profiles. In this case, the combination of the kinoform profiles enable to
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efficiently design a multifocal diffractive lens with a diffraction grating geometry that
causes negative-order light to produce a focal point for far vison, 0-order light to produce
a focal point nearer to the multifocal diffractive lens than that for far vision, and positiveorder light to further produce a focal point nearer to the multifocal diffractive lens than
that of 0-order light.
[10] In still another aspect of the present invention, a correction term of a medium
refractive index is added to the kinoform profiles. In this case, it is possible to correct a
kinoform sag height by the correction term of the medium refractive index with an
assumption of placement in liquid for in-eye use of the multifocal diffractive lens.
[11] In still another aspect of the present invention, a correction term of the pupil dilation
ratio is added to the kinoform profiles. The correction term of the pupil dilation ratio
enables to achieve matching the power acquired for diffracted light with that of refracted
light, even when simulations using design values for two methods where one of which is a
method that adds refracted light power by modifying the curvature and the other is a
method that adds diffracted light power by using a diffraction grating has proved that
acquired power values are different although these two methods are intended to add the
same power value.
[12] In still another aspect of the present invention, the multifocal diffractive lens is a
trifocal diffractive lens that has one additional focal point in addition to two focal points
produced by a bifocal diffractive lens. The near addition power of the trifocal diffractive
lens is twice of that of the bifocal diffractive lens, and the number of diffraction fringes is
the same between the bifocal diffractive lens and the trifocal diffractive lens.
[13] In still another aspect of the present invention, the multifocal diffractive lens is a
quadrifocal diffractive lens that has two additional focal points in addition to two focal
points produced by a bifocal diffractive lens. The near addition power of the quadrifocal
diffractive lens is three times of that of the bifocal diffractive lens, and the number of
diffraction fringes is the same between the bifocal diffractive lens and the quadrifocal
diffractive lens.
[14] In still another aspect of the present invention, the diffraction grating is in a
combined shape of two kinoform profiles and has a height of half of a diffraction grating
height of the two kinoform profiles. Light is allocated to negative-order light that
produces a focal point farther from the multifocal diffractive lens than that of the 0-order
light and positive-order light that produces a focal point nearer to the multifocal
diffractive lens than that of the 0-order light. The order of the negative-order light is the
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same as the order of the positive-order light. In this case, the amounts of changes of the
diffraction grating heights caused by the combining are the same, making it possible to
substantially equalize the light allocation proportions to the negative-order light and the
positive-order light.
[15] In still another aspect of the present invention, the diffraction grating is in a
combined shape of two kinoform profiles. The diffraction grating heights of the two
kinoform profiles are different from each other. Light is allocated to negative-order light
that produces a focal point farther from the multifocal diffractive lens than that of the 0-
order light and positive-order light that produces a focal point nearer to the multifocal
diffractive lens than that of the 0-order light. The order of the negative-order light and
the order of the positive-order light are different from each other. In this case, the
diffraction order light that produces focal points is increased, providing larger adjustment
amounts for focal points.
[16] In still another aspect of the present invention, a jagged part of the diffraction grating
includes planarized regions. In this case, light potentially allocated to an unintended
focal position of high-order light if the jagged part is not planarized can be allocated to a
focal position of low-order light.
[17] In still another aspect of the present invention, the multifocal diffractive lens is
formed of optical material with normal dispersion with a material refractive index
between 1.45 and 1.56, inclusive, at a wavelength of 546 nm. Power setting between
respective focal points is 0.75D or more.
[18] In still another aspect of the present invention, the multifocal diffractive lens has a
pair of optical surfaces. One of the pair of optical surfaces includes the diffraction
grating, and the other optical surface is in a toric shape. In this case, a multifocal
diffractive lens for astigmatism correction is provided due to the toric shape of the other
optical surface.

WE CLAIMS:
1. A multifocal diffractive lens, comprising a diffraction grating,
wherein negative-order light produces a focal point for far vision and 0-order light
produces a focal point nearer to the multifocal diffractive lens than that for the far
vision,
wherein positive-order light produces a focal point nearer to the multifocal diffractive
lens than that of the 0-order light,
wherein a number of focal points is three or more,
wherein the diffraction grating is in a combined shape of kinoform profiles, and
wherein a focal position for the far vision in polychromatic performance evaluation is
located nearer to the multifocal diffractive lens than the focal position for the far
vision in monochromatic performance evaluation.
2. The multifocal diffractive lens of claim 1,
wherein a correction term of a medium refractive index is added to the kinoform profiles.
3. The multifocal diffractive lens of claim 1 or 2,
wherein a correction term of a pupil dilation ratio is added to the kinoform profiles.
4. The multifocal diffractive lens of any one of claims 1, 2, and 3,
wherein the multifocal diffractive lens is a trifocal diffractive lens that has one additional
focal point in addition to two focal points produced by a bifocal diffractive lens,
wherein a near addition power of the trifocal diffractive lens is twice of that of the
bifocal diffractive lens, and
wherein a number of diffraction fringes is the same between the bifocal diffractive lens
and the trifocal diffractive lens.
5. The multifocal diffractive lens of any one of claims 1, 2, and 3,
wherein the multifocal diffractive lens is a quadrifocal diffractive lens that has two
additional focal points in addition to two focal points produced by a bifocal
diffractive lens,
wherein a near addition power of the quadrifocal diffractive lens is three times of that of
the bifocal diffractive lens, and
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wherein a number of diffraction fringes is the same between the bifocal diffractive lens
and the quadrifocal diffractive lens.
6. The multifocal diffractive lens of any one of claims 1 and 2 to 4,
wherein the diffraction grating is in a combined shape of two kinoform profiles and has a
height of half of a diffraction grating height of the two kinoform profiles,
wherein light is allocated to negative-order light that produces a focal point farther from
the multifocal diffractive lens than that of the 0-order light and positive-order light
that produces a focal point nearer to the multifocal diffractive lens than that of the
0-order light, and
wherein an order of the negative-order light is the same as an order of the positive-order
light.
7. The multifocal diffractive lens of any one of claims 1, 2, 3, and 5,
wherein the diffraction grating is in a combined shape of two kinoform profiles,
wherein diffraction grating heights of the two kinoform profiles are different from each
other,
wherein light is allocated to negative-order light that produces a focal point farther from
the multifocal diffractive lens than that of the 0-order light and positive-order light
that produces a focal point nearer to the multifocal diffractive lens than that of the
0-order light, and
wherein an order of the negative-order light and an order of the positive-order light are
different from each other.
8. The multifocal diffractive lens of any one of claims 1 and 2 to 7,
wherein a jagged part of the diffraction grating comprises planarized regions.
9. The multifocal diffractive lens of any one of claims 1 and 2 to 8,
wherein the multifocal diffractive lens is formed of optical material with normal
dispersion with a material refractive index between 1.45 and 1.56, inclusive, at a
wavelength of 546 nm, and
wherein power setting between respective focal points is 0.75D or more.
10. The multifocal diffractive lens of any one of claims 1 and 2 to 9,
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wherein the multifocal diffractive lens has a pair of optical surfaces,
wherein one of the pair of optical surfaces includes the diffraction grating, and
wherein the other of the pair of optical surfaces is in a toric shape.
11. The multifocal diffractive lens of any one of claims 1 and 2 to 10,
wherein the diffraction grating is in a combined shape of a diffraction grating geometry
with a positive-power addition and a diffraction grating geometry with a negativepower addition.
12. The multifocal diffractive lens of any one of claims 1, 2 to 4, and 6,
wherein the multifocal diffractive lens is a trifocal diffractive lens of -1-order, 0-order,
and +1-order,
wherein the diffraction grating is in a combined shape of a first kinoform profile with a
diffraction grating geometry with a positive-power addition corresponding to +1-
order light and the 0-order light and a second kinoform profile with a diffraction
grating geometry with a negative-power addition corresponding to -1-order light
and the 0-order light.
13. The multifocal diffractive lens of any one of claims 1, 2, 3, 5, and 7,
wherein the multifocal diffractive lens is a quadrifocal diffractive lens of -1-order, 0-
order, +1-order, and +2-order,
wherein the diffraction grating is in a combined shape of a first kinoform profile with a
diffraction grating geometry with a positive-power addition corresponding to +1-
order light and +2-order light and a second kinoform profile with a diffraction
grating geometry with a negative-power addition corresponding to -1-order light
and the 0-order light.