Patent Application
20080147185
The present invention relates generally to ophthalmic lenses, and more particularly, to ophthalmic lenses that provide compensation for the chromatic aberrations of the eye.
The refractive power of the human eye varies as a function of the wavelength of incident radiation such that the eye is more myopic for blue light and more hyperopic for red light. For example, the optical power of the eye can vary by about 2 Diopters (D) over a wavelength range of 400 nm to 700 nm. This change of optical power as a function of wavelength, which is commonly known as chromatic aberration or chromatic defocus, can degrade the image contrast. Such chromatic aberrations can adversely affect the optical performance of ocular ophthalmic lenses and implants, which are utilized by a growing segment of the population. In addition, ocular ophthalmic lenses and implants generally exhibit chromatic aberrations of their own, which can further degrade their optical performance.
Accordingly, there is a need for enhanced ophthalmic lenses, such as intraocular lenses, that provide better optical performance for polychromatic incident light.
The present invention is generally directed to multi-element intraocular lenses (IOLs) that can compensate for natural chromatic aberrations of the eye, particularly the longitudinal chromatic aberration. More specifically, various parameters of the lens elements, such as their chromatic dispersions (variations of index of refraction as a function of wavelength) as well as surface curvatures, are adapted so that those elements collectively provide a desired degree of chromatic aberration correction.
In one aspect, the invention provides an intraocular lens that includes a posterior optic and an anterior optic. The optics have different chromatic dispersions adapted to cooperatively provide compensation for natural chromatic aberrations of the eye over a wavelength range of interest. In other words, the optics are adapted to at least partially correct the effects of the chromatic aberrations exhibited by the eye (variations of focal lengths for different wavelength components of incident light).
In a related aspect, the wavelength range over which the compensation of the chromatic aberration is achieved can be centered about 570 nm, and extend from about 400 nm to about 700 nm. By way of example, the optics can be adapted to collectively provide a chromatic aberration correction in a range of about 0.5 to about 3.5 Diopters over a wavelength range of about 400 nm to about 700 nm.
In another aspect, one of the optics provides a positive optical power and the other provides a negative optical power. In many cases, the optics jointly provide a total optical power in a range of about 6 Diopters to about 34 Diopters.
The optics can be axially separated, or can be in contact via two of their surfaces. More generally, the distance between the optics (e.g., separation between centers of the optics) can be in a range of about 0 to about 5 millimeters (e.g., in a range of about 0.1 to about 5 mm). Further, an optical axis of one optic can be preferably substantially coincident with an optical axis of the other optic.
In a related aspect, both optics are formed of a biocompatible material. Some examples of such materials include, without limitation, soft acrylic polymers with sub-ambient glass transition temperatures, hydrogel, polymethylmethacrylate, polysulfone, polystyrene, cellulose acetate butyrate or other biocompatible polymeric materials having a requisite index of refraction for a particular application. By way of example, in some cases, one optic is formed of polymethylmethacrylate (PMMA) and the other is formed of polysulfone. In another example, one optic is formed of a soft acrylic material (a cross-linked copolymer of 2-phenylethyl acrylate and 2-phenylethyl methacrylate) known as Acrysof and the other optic is formed of a cross-linked terpolymer of ethyl acrylate, ethylmethacrylate and 2,2,2-trifluoroethyl methacrylate commonly known as Sensar.
In another aspect, an intraocular lens is disclosed that includes a posterior optic exhibiting a chromatic dispersion over a wavelength range, and an anterior optic exhibiting a different chromatic dispersion over that wavelength range. The optics include a plurality of curved surfaces having curvatures that are adapted to generate, together with the difference in the chromatic dispersions of the optics, chromatic focal shifts for compensating chromatic aberrations of the eye over that wavelength range.
In a related aspect, the chromatic focal shifts provide a correction in a range of about 0.5 Diopters to about 3.5 Diopters over the wavelength range of interest, which can extend, e.g., from about 400 nm to about 700 nm.
In another aspect, an ophthalmic lens system is disclosed that includes a posterior lens and an anterior lens. A diffractive pattern is disposed on a surface of one of those lenses such that the lenses cooperatively provide a near focus and a far focus. The anterior and posterior lenses exhibit different chromatic dispersions adapted to compensate for chromatic aberration of the eye at the far focus over a wavelength range, e.g., over a wavelength range of about 400 nm to about 700 nm.
In a related aspect, the optical power associated with the far focus is in a range of about 6 D and 34 D, and the diffractive pattern provides an add power in a range of about 1 to about 6 D.
In another aspect, the invention provides an intraocular lens system that includes a posterior optic and an anterior optic. The optics are movably coupled to one another so as to allow movement of at least one optic, in response to application of a compressive force thereto, relative to the other. Further, the optics have different chromatic dispersions adapted to cooperatively provide compensation for natural chromatic aberrations of the eye over a wavelength range.
In a related aspect, the above lens system provides an accommodation (pseudo-accommodation) in a range of about 1 to about 6 Diopters when implanted in a patient's eye.
In another aspect, in the above pseudo-accommodative lens system, the optics are adapted to collectively provide a chromatic aberration correction in a range of about 0.5 to about 3.5 Diopters over a wavelength range extending from about 400 nm to about 700 nm.
In another aspect, in the above pseudo-accommodative lens system, one optic provides a positive optical power (e.g., in a range of about 20 D to about 80 D) while the other optic provides a negative optical power (e.g., in a range of about −5 D to about −60 D). Further, the optics can be formed of two different materials, preferably biocompatible, whose Abbe numbers differ by at least about 10. For example, one optic can be formed of PMMA and the other of a soft acrylic material. In another example, one of the optics can be formed of a cross-linked copolymer of 2-phenylethyl acrylate and 2-phenylethyl methacrylate and the other optic can be formed of a cross-linked terpolymer of ethyl acrylate, ethylmethacrylate, and 2,2,2-trifluoroethyl methacrylate.
Further understanding of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, described briefly below.
The present invention generally provides ophthalmic lenses that are capable of compensating, either fully or partially, for the natural chromatic aberrations of the eye. Although the following embodiments are primarily directed to intraocular lenses, the teachings of the invention can be applied to a variety of lenses and ocular implants, such as, contact lenses. Further, the terms “intraocular lens” and its abbreviation “IOL” are used herein interchangeably to describe lenses that are implanted into the interior of an eye to either replace the eye's natural lens or to otherwise augment vision regardless of whether or not the natural lens is removed.
With reference to
Although in this embodiment the lenses 12 and 14 are in contact with one another, in other embodiments they can be separated along an axial direction by a distance, e.g., less than about 5 mm. In many embodiments in which the lenses are axially separated, they are preferably positioned relative to one another such that their optical axes are aligned. By way of example,
Referring again to
where nD, nF and nC represent the refractive indices of the material at wavelengths of 589.2 nm, 486.1 nm and 656.3 nm, respectively, that correspond to Fraunhofer D-, F-, and C-spectral lines. In general, materials having high values of V exhibit low dispersions. In many embodiments, the materials forming the lenses 12 and 14 have sufficiently different V numbers so as to minimize, and in some cases eliminate, the chromatic aberration of the IOL 10 and/or cause the net power of the IOL 10 to vary as function of incident light wavelength in a manner that would compensate for (counter) chromatic dependent refractive error of the eye.
By way of example, the chromatic aberration exhibited by the IOL can be in a range of about 0.5 D to about 3.5 D. Further, in some embodiments, the materials forming the lenses 12 and 14, and the relative power of the two lenses, are selected so as to compensate for natural chromatic aberrations of the eye over a wavelength range, e.g., a wavelengths range of about 400 nm to about 700 nm. The phrase “to compensate for natural chromatic aberrations of the eye,” as used herein is intended to encompass not only those cases in which the chromatic aberrations are fully counteracted but also cases in which some residual chromatic aberrations remain, e.g., a residual longitudinal aberration less than about 50%. For example, the IOL 10 can provide a chromatic aberration correction in a range of about 1 to about 2 Diopters over a wavelength range of about 400 nm to about 700 nm.
The lenses 12 and 14 can be formed from a variety of materials, which are preferably biocompatible. By way of example, one lens (e.g., lens 14) can be made from polymethylmethacrylate (PMMA) (Abbe number V=55) and the other lens (e.g., lens 12) can be made from polysulfone (Abbe number V=30.87). Other suitable materials include, without limitation, soft acrylics, such as Acrysof (cross-linked copolymer of 2-phenylethyl acrylate and 2-phenylethyl methacrylate, (Abbe number V of about 37), polystyrene (Abbe number V=30.87), polycarbonate (Abbe number V of 29.9), or cellulose acetate butyrate (Abbe number V in a range of about 80 to 84), and the materials disclosed in U.S. Pat. No. 4,834,750 that is herein incorporated by reference, so long as the differences between the Abbe numbers of the materials forming the two lenses are sufficiently large (e.g., greater than about 10) to provide a desired chromatic compensation. For example, in one embodiment, lenses 12 and 14 can be made, respectively, from PMMA and Acrysof with the lens 12 having an optical power of about −43.17 Diopters and the lens 14 having an optical power of about +64.17 Diopters.
In some embodiments, the lens 12 having a positive optical power can be formed of a material with low dispersion (high V number) and the lens 14 having a negative optical power can be formed of a material with higher dispersion (lower V number) such that the combined optical power of the two lenses is positive.
An achromatizing IOL of the invention can be employed for capsule implantation in an aphakic eye or for anterior or posterior implantation in a phakic eye.
By way of illustration, a prototype achromatizing doublet lens, such as the above lens 10, was theoretically designed by utilizing a model eye with an aspheric cornea characterized by a conic constant (cc) of −0.183 and OSLO™ lens design software, marketed by Lambda Research Corporation of Littleton, Mass., U.S.A. An aperture of about 4.5 mm at the pupil plane of the model eye was employed and the wavelengths of 550, 488 and 633 nm were weighted to approximate photopic response of the eye.
The following relation among the V numbers of the two lenses and their respective optical powers were utilized in these design examples:
where φ1 and φ2 represent the optical powers of the two lenses, and V1 and V2 are the Abbe numbers of the materials from which the two lenses are formed.
In the illustrative design, the material of one lens was selected to have a low refractive index and a high Abbe number while the material of the other lens was selected to have a high refractive index and a low Abbe number. The lens formed of the material having a lower refractive index was chosen to have a positive optical power while the lens formed of the material having a higher refractive index was selected to have a negative optical power.
As a comparative reference for evaluating the achromatizing design, the chromatic properties of a pseudophakic model eye having an aspheric monofocal implant formed of soft acrylic material (a material used in an implant marketed as Acrysof™) were calculated. More specifically, the following model eye was set up in OSLO design software for these calculations:
As shown in the Table 2 below, the above pseudophakic eye exhibits a power change of 3.16 D over a wavelength range of 400 to 700 nm and a power change of 1.41 D over a wavelength range of 488 to 656 nm.
In the lens design example, the properties of an achromatic doublet lens having an equiconvex PMMA positive lens (with an optical power of 39 D) and a meniscus polysulfone (V=22.5) lens (with an optical power of −19 D) in contact with a posterior surface of the PMMA lens were evaluated. This doublet lens was substituted for the monofocal IOL in the above eye model, as shown schematically in
In another case, the PMMA/polysulfone lens was incorporated in the eye model, but the lens parameters were optimized to correct half of the chromatic aberration associated with the reference eye model. A polychromatic MTF associated with this case, shown in
In some embodiments, an achromatizing doublet includes a positive lens formed of a material utilized in commercially available lenses sold under trademark Acrysof (cross-linked copolymer of 2-phenylethyl acrylate and 2-phenylethyl methacrylate), and a negative lens formed of a material commonly known as Sensar (cross-linked terpolymer of ethyl acrylate, ethylmethacrylate, and 2,2,2-trifluoroethyl methacrylate). By way of illustration, the optical property of such an achromatizing multifocal doublet was simulated by computing the polychromatic MTF exhibited by an average eye model in which the doublet was incorporated. More specifically, a doublet lens having a negative Acrysof multifocal lens having a distance power of about −15 D and a positive Sensar lens having a power of about 35 D was incorporated in an average model eye, and a polychromatic MTF (wavelengths of 488 nm, 550 nm and 633 nm) was calculated at the focal plane of the model. The two lenses were configured to provide 1.26 D of chromatic aberration correction.
The teachings of the invention can also be applied to multi-focal ophthalmic lenses, such as, intraocular lenses that can provide both near and far vision. By way of example,
By way of example, the step height at each zone boundary of the diffractive pattern can be defined in accordance with the following relation:
wherein
λ denotes a design wavelength (e.g., 550 nm),
α denotes a parameter that can be adjusted to control diffraction efficiency associated with various orders, e.g., a can be selected to be 2.5,
n2 denotes the index of refraction of the optic,
n1 denotes the refractive index of a medium in which the lens is placed, and ƒapodize represents a scaling function whose value decreases as a function of increasing distance from the intersection of an optical axis with the anterior surface of the lens. By way of example, the scaling function ƒapodize can be defined by the following relation:
wherein
ri denotes the radial distance of the ith zone,
rout denotes the outer radius of the last diffractive zone.
Other apodization scaling functions can also be employed, such as those disclosed in a co-pending patent application entitled “Apodized Aspheric Diffractive Lenses,” filed Dec. 1, 2004 and having a Ser. No. 11/000770, which is herein incorporated by reference.
The diffractive pattern 26 covers a portion of the anterior surface (it is truncated) and is surrounded by a refractive portion of the surface lacking diffractive structures.
In this embodiment, the lens 22 provides a positive optical power (e.g., an optical power in a range of about 20 D to about 80 D) and the lens 24 provides a negative optical power (e.g., a power in a range of about −5 D to about −60 D), although the signs of the optical powers of the lenses can also be reversed. In many embodiments, the materials from which the lenses 22 and 24 are formed are selected to have sufficiently different refractive dispersions so as to allow compensating for the natural chromatic aberrations of the eye at the far focus. By way of example, the materials described above in connection with the previous embodiments can be utilized to form the lenses 22 and 24. For example, in one embodiment, the lens 22 can be formed of Acrysof lens material and the lens 24 can be formed of Sensar lens material.
In some embodiments, the ophthalmic lens 20 is configured to provide partial compensation of the eye's chromatic aberration. For example, it can be adapted, in a manner discussed above, to correct about 50% of the eye's longitudinal chromatic aberration. In other embodiments, the lens 20 is adapted to provide a full compensation for the eye's chromatic aberrations.
In some embodiments, multi-optic intraocular systems are disclosed that not only provide compensation for natural chromatic aberrations of the eye but also provide some degree of accommodation, e.g., in a range of about 1 to about 6 Diopters. By way of example,
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.
