The present invention relates generally to ophthalmic lenses (e.g., intraocular lenses) and methods of correcting vision, and more particularly, to such lenses and methods that can better address the particular visual needs of individual patients and/or patient groups.
Intraocular lenses (IOLs) are routinely implanted in patients' eyes during cataract surgery to replace the natural crystalline lens. Some IOLs exhibit both a far-focus power as well as a near-focus power in order to provide a patient not only with far but also near vision. However, the visual needs of different patients, and/or patient groups, typically vary. For example, some patients may favor near vision over far vision, or vice versa. Moreover, the eyes of different patients can exhibit varying ocular parameters (e.g., different maximum pupil sizes). As a result, an IOL that provides an optimal performance for one patient may not perform as well for another patient.
Conventional IOLs and methods of their use for correcting vision, however, do not take into account such variations in patients' needs or ocular parameters.
Hence, there is a need for enhanced methods and ophthalmic lenses for correcting vision, and more particularly, for such methods and lenses that can be employed to compensate for the lost optical power of a removed natural lens.
In one aspect, the present invention provides a method of designing a diffractive ophthalmic lens (e.g., an intraocular lens (IOL)) that includes providing an optic having an anterior refractive surface and a posterior refractive surface, wherein the optic provides a far-focus power. The far-focus optical power can be in a range of about 6 Diopters (D) to about 34 D, e.g., in a range of about 10 D to about 30 D or in a range of about 18 D to about 26 D. Further, in some cases, the far-focus optical power can be in a range of about −5 D to about 5.5 D. A truncated diffractive structure can be disposed on at least one of the surfaces for generating a near-focus add power, for example, in a range of about 2 D to about 4 D, e.g., in a range of about 2.5 D to about 4 D or in a range of about 3 D to about 4 D. And the diffractive structure can be adjusted so as to obtain a desired distribution of optical energy between the near and far foci for a range of pupil sizes. The term “truncated diffractive structure,” as used herein, refers to a diffractive structure that covers a portion, rather than the entirety, of an optical surface of a lens. Further, the effective add power of the IOL when implanted in the eye can be different than its nominal (actual) add power. For example, the combination of the corneal power and the separation between the cornea and the IOL can weaken the IOL's effective add power, e.g., a nominal 4 D add power can result in a 3 D effective add power for the whole eye. In the following sections, unless otherwise indicated, the recited values of add power refer to the lens's nominal (actual) add power, which can be different that the effective add power when the IOL is implanted in the eye.
In another aspect, the diffractive structure is selected so as to obtain a desired shift in a ratio of optical energy in the far-focus relative to the energy in the near-focus as the pupil size varies over a range.
In a related aspect, adjusting the diffractive structure comprises selecting a diameter of the structure and/or the step heights of a plurality of diffractive elements forming that structure.
In another aspect, the diffractive structure can comprise a plurality of diffractive zones that exhibit apodized step heights at their boundaries. In some cases, the number of the diffractive zones can be adjusted to obtain a desired distribution of the optical energy between the near and far foci for a range of pupil sizes. Alternatively, or in addition, the variation of the step heights at the boundaries of the diffractive zones can be adjusted so as to obtain a desired energy distribution.
In another aspect, a method of designing an ophthalmic lens is disclosed that includes providing an optic that exhibits a far focus and a near focus, wherein the optic includes a diffractive structure on at least one surface thereof for generating the near focus. The diffractive structure is adjusted so as to obtain a desired distribution of optical energy between the far and near foci over a range of pupil sizes based on visual needs of a patient population. By way of example, the diffractive structure is adjusted to obtain the desired energy distribution at a design wavelength (e.g., at 550 nm).
In a related aspect, the patient population comprises patients having typical pupil diameters under photopic conditions in a range of about 2 mm to about 5 mm. In some cases, the patient population is one that favors far vision over near vision, or alternatively, favors near vision over far vision.
In another aspect, in the above method, the diffractive structure is adjusted by selecting a particular variation of step heights at boundaries of a plurality of diffractive zones, which form the structure.
In other aspects, the invention provides a method of correcting vision of a patient. The method calls for providing a lens that exhibits a far-focus power and a near focus-power for implantation in one eye of the patient, and providing another lens, which exhibits a substantially similar far-focus power but a different near-focus power, for implantation in the other eye of the patient.
In a related aspect, in the above method of correcting a patient's vision, the difference between the near-focus powers of the two lenses is selected so as to enhance the near vision range of the patient and/or to provide the patient with intermediate vision. For example, the far-focus power of each lens can be in a range of about 6 D to about 34 D while the difference between the near-focus powers of the lenses can range from about 0.2 D to about 1.5 D. For example, one lens can exhibit a near-focus power of about 4 D while the other exhibits a near-focus power of about 3 D. Alternatively, one lens can provide a near-focus power of about 4 D while the other provides a near focus power of about 3.25 or 3.75 D.
In another aspect, an ophthalmic lens is disclosed that includes an optic having an anterior surface and a posterior surface, and a diffractive structure disposed on at least one of those surfaces. The diffractive structure comprises a plurality of diffractive zones separated from one another by a plurality of steps having decreasing heights as a function of increasing radial distance from an apex of that surface. For example, the step heights can be defined in accordance with the following relation:
wherein
wherein
In a related aspect, in the above ophthalmic lens, the index of refraction of the material forming the lens (n2) can be in a range of about 1.4 to about 1.6 (e.g., the lens can be formed of a lens material commonly known as Acrysof (a cross-linked copolymer of 2-phenylethyl acrylate and 2-phenylethyl methacrylate) having an index of refraction of 1.55). In many embodiments, the index of refraction of the surrounding medium is taken to be about 1.336. In some embodiments, the parameters phase0, rcontro, rolloff can be, respectively, in a range of about 0.4 to about 0.7, in a range of about 1 to about 2, and in a range of about 5 to about 200.
In another aspect, in the above ophthalmic lens, at least one of the anterior and posterior surfaces includes an aspheric base profile, e.g., an aspheric profile characterized by a conic constant in a range of about −10 to about −100 for the Acrysof lens material, and corresponding values can be utilized for other lens materials. In some cases, the aspheric profile can be characterized by the following relation:
wherein,
z denotes the surface sag at a radial location r from the apex of the surface (the intersection of the optical axis with the surface),
c denotes the curvature of the surface at its apex,
r denotes the radial distance from the apex of the surface, and
k denotes the conic constant. In some embodiments, the parameter c can range, e.g., from about 0.01 mm−1 to about 0.1 mm−1, while parameter k (the conic constant) can range from about −10 to about −1000.
In other aspects, an ophthalmic lens is disclosed that includes an optic comprising an anterior surface and a posterior surface. The lens can further include a diffractive structure disposed on a central portion of at least one of those surfaces, where the diffractive structure is surrounded by a peripheral portion of the surface that is devoid of diffractive elements. One of the central or the peripheral portions includes an aspheric base profile while the other includes a spherical base profile. By way of example, the central portion can exhibit a spherical profile while the peripheral portion exhibits an aspherical profile characterized (e.g., by a conic constant in a range of about −10 to about −1000) or vice versa. In some cases, the aspheric portion can be characterized by the above relation indicating the surface sag as a function of radial distance from the optical axis.
In another aspect, an intraocular lens is disclosed that includes an anterior surface and a posterior surface, on one of which a truncated diffractive structure is disposed. The diffractive structure can be characterized by a substantially uniform step height separating adjacent diffractive elements forming the structure, or alternatively, can be characterized by apodized step heights in accordance with the above apodization function. At least one of the anterior or posterior surfaces exhibits a toric profile.
In other aspects, the above intraocular lenses can be formed from materials that provide some filtering of the blue light (e.g., wavelengths in a range of about 400 nm to about 500 nm)
Further understanding of the invention can be obtained by reference to the following detailed description, in conjunction with the associated drawings, which are described briefly below.
The present invention generally refers to diffractive ophthalmic lenses and methods for correcting vision that employ such lenses. In the embodiments that follow, the salient features of various aspects of the invention are discussed in connection with intraocular lenses (IOLs). The teachings of the invention can also be applied to other ophthalmic lenses, such as contact lenses. The term “intraocular lens” and its abbreviation “IOL” are used herein interchangeably to describe lenses that are implanted into the interior of the eye to either replace the eye's natural lens or to otherwise augment vision regardless of whether or not the natural lens is removed. Intracorneal lenses and phakic intraocular lenses are examples of lenses that may be implanted into the eye without removal of the natural lens.
By way of example, in some embodiments, the present invention provides a method of designing an ophthalmic lens, which utilizes a diffractive structure to optimize the visual performance of the lens by adjusting the distribution of optical energy directed to a near focus and a far focus for a range of pupil sizes. With reference to a flow chart illustrated in
As discussed in more detail below, a number of parameters of the diffractive structure can be varied so as to adjust the distribution of the optical energy between the near and far foci. For example, the size of the diffractive structure, e.g., its radial extent and/or a number of diffractive zones comprising the structure, can be adjusted to obtain a desired shift in a ratio of optical energy in the far-focus relative to energy in the near-focus as the pupil size varies over a pre-defined range. As another example, in embodiments in which the diffractive structure is formed by a plurality of diffractive zones that exhibit apodized step heights at their boundaries, the variation of the step heights can be designed to obtain a desired distribution of energy between the near and far foci. A variation of the step heights is typically accompanied by changes in other parameters of the diffractive structure, such as the surface curvature within a diffractive zone.
In some embodiments, the above method can be utilized to address differences in visual needs among different patients. For example, variations of the pupil diameter (e.g., typical pupil diameter) among different patients can be addressed by providing different diffractive structures, each designed to provide a particular distribution of optical energy between the near and far foci for a given range of pupil sizes. Further, the methods of the invention can be utilized to design an ophthalmic lens that is particularly suited to the visual needs of a patient, or a group of patients. For example, for patients who favor distance vision over near vision, the diffractive structure can be selected to transmit more of the optical energy to the far focus rather than the near focus. Alternatively, the diffractive structure can be designed to emphasize near vision.
The methods of the invention can be applied to design a variety of diffractive ophthalmic lenses. By way of example,
The lens 18 can be formed of a variety of materials, preferably biocompatible. Some examples of suitable materials include, without limitation, a soft acrylic material utilized for forming commercial lenses commonly known as Acrysof, silicone and hydrogel. By way of further examples, U.S. Pat. No. 6,416,550, which is herein incorporated by reference, discloses materials suitable for forming the IOL 18.
With reference to
r
i
2
=r
0
2+2iλf Eq. (1)
wherein
i denotes the zone number (i=0 denotes the central zone)
λ denotes the design wavelength,
f denotes a focal length of the near focus, and
r0 denotes the radius of the central zone
In some embodiments, the design wavelength λ is chosen to be 550 nm green light at the center of visual response. In some cases, the radius of the central zone (r0) can be set to be 2 f.
Further, the step height between adjacent zones can be defined in accordance with the following relation:
wherein
λ denotes the design wavelength (e.g., 550 nm),
n2 denotes the refractive index of the material from which the lens is formed,
n1 denotes the refractive index of the medium in which the lens is placed, and
p is a fraction, e.g., 0.5 or 0.7.
The diffractive structure 28 can be adjusted to shift the ratio of optical energy directed to the near and far foci. For example, the diameter of the diffractive structure 28 can be adjusted to vary this ratio. By way of example,
In some embodiments, the height of the step at the zone boundaries of the diffractive structure in the above diffractive lens 20 can be adjusted so as to shift the energy balance between the near and far foci. By way of example,
In some embodiments, the step heights at the diffractive zones vary as a function of their radial distance from the optical axis, that is, the step heights are apodized. By way of example,
wherein
p is a phase height,
λ is a design wavelength (e.g., 550 nm),
n2 is the refractive index of the material forming the lens, and
n1 is the index of refraction of the medium surrounding the lens,
fapodize denotes an apodization function.
A variety of apodization functions can be employed. For example, in some embodiments, the apodization function is defined in accordance with the following relation:
wherein
ri denotes the distance of each radial zone boundary from the intersection of the optical axis with the surface,
rin denotes the inner boundary of the apodization zone,
rout denotes the outer boundary of the apodization zone, and
exp denotes an exponent to obtain a desired reduction in the step heights. Further details regarding apodization of the step heights can be found, e.g., in U.S. Pat. No. 5,699,142, which is herein incorporated by reference.
The above energy distribution curves indicate that various parameters of an apodized diffractive structure (e.g., the diameter of the diffractive structure, phase height, and apodization exponent) can be adjusted to optimize the performance of the lens for a particular patient and/or a patient group. For example, for a patient, or a patient group, that favors near vision over far vision, a diffractive structure with a larger diameter can be selected to divert more of the incident energy to the near focus (i.e., 1st order diffraction).
In another embodiment, a different apodization of the step heights of the diffractive structure can be employed to obtain a different set of energy distribution curves indicative of the ratio of the incident light energy directed to the near and far foci. In one such embodiment, the phase delay at each diffractive step can be defined in accordance with the following relation:
wherein
b represents the phase delay as a fraction of 2π,
phase0 represents the overall (cumulative) optical phase delay across the diffractive steps,
rcontrol represents the overall extent of the apodization region,
rolloff defines the steepness of the slope of the apodization profile.
And the local diffraction efficiency as a function of radial distance from the lens center (r) can be determined in accordance with the following relation:
wherein the parameter α can be defined in accordance with the following relation:
α=π*(b−p) Eq. (7)
wherein b is defined above, and p denotes the diffraction order. The zeroth order diffraction is typically associated with the distance lens power.
The physical heights of the diffractive steps as a function of radial distance from the lens center can then be given by the following relation:
wherein
h represents the physical step height,
λ denotes the design wavelength (e.g., 550 nm),
n1 denotes the refractive index of a medium surrounding the lens (e.g., 1.336 of IOLs), and
n2 denotes the refractive index of the material forming the lens (e.g., 1.55 when Acrysoft is used to form the lens)
In some embodiments, the step heights follow the above relation up to a selected threshold step height (i.e., up to a certain radial location), beyond which the remaining step heights (the step heights at greater radial distances) decrease linearly to zero.
The parameters associated with the above step height apodization function (Eq. 8), such as phase0, rolloff, rcontrol, can be adjusted to shift the distribution of the optical energy between the near and far foci of a diffractive lens. By way of example,
These graphs show that energy balance between the far-focus and the near-focus lens power as a function of the pupil size can be adjusted by varying one or more of the apodization parameters. For example, the parameters can be selected to maintain a substantially constant ratio of the optical energy directed to the near and far foci up to a selected pupil size, and to provide a ratio that varies as the pupil size grows beyond the selected value (e.g., the energy ratio would favor directing more of the light to the far focus for large pupil sizes).
In some embodiments, one or more surfaces of the IOL can include an aspherical profile so as to reduce spherical aberration. For example,
wherein,
z denotes the surface sag at a radial location r from the apex of the surface (the intersection of the optical axis with the surface),
c denotes the curvature of the surface at its apex,
r denotes the radial distance from the apex of the surface, and
k denotes the conic constant. By way of example, in some embodiments in which the lens is formed of Acrysof lens material, the conic constant (k) can be in a range of about −10 to about −1000.
In other aspects, the present invention discloses methods for correcting vision that can enhance the range of a patient's near vision and/or to provide a patient with not only far and near vision but also an intermediate vision. For example, one diffractive IOL having one add power can be implanted in one eye of a patient and another diffractive IOL having a different add power can be implanted in the other eye. The difference in the add powers can be, e.g., in a range of about 0.1 D to about 1.5 D (e.g., in a range of about 0.2 to 1 D). For example, a combination of the following add powers can be employed to enhance a patient's range of near vision: 4 D, 3.75 D, 3.5 D, 3.25 D and 3 D. In some embodiments, two diffractive IOLs having substantially similar far focus powers but different add powers can be implanted in a patient's eyes (each in one eye of the patient) such that the IOL with the lower add power would provide a degree of intermediate vision and/or enhance the range of the near vision. In some embodiments, the difference between the add powers of the two lenses can be selected such that their near vision energy curves would at least partially overlap so as to enhance the depth of focus for near vision.
The above method of implanting a different IOL in each eye of a patient can be combined with the previous methods of optimizing the distribution of energy between the near and far foci so as to enhance a patient's vision. For example, for a patient favoring near and intermediate vision over far vision, the diffractive structures of the lenses can be adjusted, in a manner discussed above, so as to optimize the incident light energy that is directed to the near focus over a range of pupil sizes.
In other embodiments, one or both optical surfaces of a truncated diffractive lens can exhibit a selected degree of toricity to provide, e.g., astigmatic correction. By way of example,
In some embodiments, the diffractive IOL (having a truncated diffractive structure characterized by a substantially uniform or a non-uniform step heights) can be formed of a material that can provide some filtering of the blue light. By way of example, the IOL can be formed of Acrysof Natural material. By way of further example, U.S. Pat. No. 5,470,932, herein incorporated by reference, discloses polymerizable yellow dyes that can be utilized to block or lower the intensity of blue light transmitted through ocular lenses.
The various lenses discussed above can be formed by employing manufacturing techniques known in the art.
Those having ordinary skill in the art will appreciate that various modifications can be made to the above embodiments without departing from the scope of the invention.
The present application is a divisional of U.S. patent application Ser. No. 11/444,112 filed on Aug. 23, 2006 which is a continuation-in-part (CIP) of U.S. patent application Ser. No. 11/000,770 entitled “Apodized Aspheric Diffractive Lenses,” filed on Dec. 1, 2004, both of which are herein incorporated by reference in their entirety.
Number | Date | Country | |
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Parent | 11444112 | Aug 2006 | US |
Child | 12847214 | US |
Number | Date | Country | |
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Parent | 11000770 | Dec 2004 | US |
Child | 11444112 | US |