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  Methods of obtaining ophthalmic lenses providing the eye with reduced aberrationsUSPTO Application #: 20070258044Title: Methods of obtaining ophthalmic lenses providing the eye with reduced aberrations Abstract: The present invention discloses methods of obtaining ophthalmic lens capable of reducing the aberrations of the eye comprising the steps of characterizing at least one corneal surface as a mathematical model, calculating the resulting aberrations of said corneal surface(s) by employing said mathematical model, selecting the optical power of the intraocular lens. From this information, an ophthalmic lens is modeled so a wavefront arriving from an optical system comprising said lens and corneal model obtains reduced aberrations in the eye. Also disclosed are ophthalmic lenses as obtained by the methods which are capable reducing aberrations of the eye. (end of abstract) Agent: Advanced Medical Optics, Inc. - Santa Ana, CA, US Inventors: Sverker Norrby, Pablo Artal, Patricia Ann Piers, Marrie Van Der Mooren USPTO Applicaton #: 20070258044 - Class: 351212000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070258044. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] The present application is a continuation application of U.S. Ser. No. 10/606,910, filed Jun. 26, 2003, which is a divisional application of U.S. Ser. No. 09/863,546, filed May 23, 2001, now U.S. Pat. No. 6,609,793, issued Aug. 26, 2003, which was the non-provisional application of Provisional Application No. 60/259,924 filed Jan. 5, 2001, now expired and Provisional Application No. 60/207,734 filed May 26, 2000, now expired. FIELD OF THE INVENTION [0002] The present invention relates to methods of designing ophthalmic lenses that provide the eye with reduced aberrations, as well as lenses capable of providing such-visual improvements. BACKGROUND OF THE INVENTION [0003] It is presently discussed that the visual quality of eyes having an implanted intraocular lens (IOL) is comparable with normal eyes in a population of the same age. Consequently, a 70 year old cataract patient can only expect to obtain the visual quality of a non-cataracteous person of the same age after surgical implantation of an intraocular lens, although such lenses objectively have been regarded as optically superior to the natural crystalline lens. This result is likely to be explained by the fact that present IOLs are not adapted to compensate for defects of the optical system of the human eye, namely optical aberrations. Age-related defects of the eye have recently been investigated and it is found that contrast sensitivity significantly declines in subjects older than 50 years. These results seem to comply with the above-mentioned discussion, since the contrast sensitivity measurements indicate that individuals having undergone cataract surgery with lens implantation lens will not obtain a better contrast sensitivity than non-cataracteous persons of an average age of about 60 to 70 years. [0004] Even if intraocular lenses aimed at substituting the defective cataract lens and other ophthalmic lenses, such as conventional contact lenses, have been developed with excellent optical quality as isolated elements, it is obvious that they fail to correct for a number of aberration phenomena of the eye including age-related aberration defects. [0005] U.S. Pat. No. 5,777,719 (Williams et al.) discloses a method and an apparatus for accurately measuring higher order aberrations of the eye as an optical system with wavefront analysis. By using a Hartmann-Shack wavefront sensor, it is possible to measure higher order aberrations of the eye and use such data to find compensation for these aberrations and thereby obtain sufficient information for the design of an optical lens, which can provide a highly improved optical performance. The Hartmann-Shack sensor provides means for analyzing light reflected from a point on the retina of the eye of a subject. The wavefront in the plane of the pupil is recreated in the plane of the lenslet array of the Hartmann-Shack sensor. Each lenslet in the array is used to form an aerial image of the retinal point source on a CCD camera located at the focal plane of the array. The wave aberration of the eye, in the form resulting from a point source produced on the retina by a laser beam, displaces each spot by an amount proportional to the local slope of the wavefront at each of the lenslets. The output from the CCD camera is sent to a computer, which then performs calculations to fit slope data to the first derivatives of 66 Zernike polynomials. From these calculations, coefficients for weighting the Zernike polynomials are obtained. The sum of the weighted Zernike polynomials represents a reconstructed wavefront distorted by the aberrations of the eye as an optical system. The individual Zemike polynomial terms will then represent different modes of aberration. [0006] U.S. Pat. No. 5,050,981 (Roffman) discloses another method for designing a lens by calculating modulation transfer functions from tracing a large number of rays through the lens-eye system and evaluating the distribution density of the rays in the image position. This is repeatedly performed by varying at least one lens surface until a lens is found which results in a sharp focus and a maximum modulation transfer function. [0007] U.S. Pat. No. 6,224,211 (Gordon) describes a method of improving the visual acuity of the human eye by successively fitting aspheric lenses to the cornea and thereby finding a lens that can reduce spherical aberration of the whole individual eye. [0008] The methods referred to above for designing are suitable for the design of contact lenses or other correction lenses for the phakic eye which can be perfected to compensate for the aberration of the whole eye system. However, to provide improved intraocular lenses aimed to replace the natural crystalline lens, it would be necessary to consider the aberrations of the individual parts of the eye. [0009] U.S. Pat. No. 6,050,687 (Bille et al) refers to a method wherein the refractive properties of the eye are measured and wherein consideration is taken to the contribution of the individual surfaces of the eye to the total wavefront aberrations. The method described herein particularly aims at analyzing the topography of the posterior corneal surface in order to improve refractive correction techniques. [0010] There has recently been a focus on studying the aberrations of the eye, including a number of studies of the development of these aberrations as a function of age. In two particular studies, the development of the components of the eye were examined separately, leading to the conclusion that the optical aberrations of the individual components of younger eyes cancel each other out, see Optical Letters, 1998, Vol. 23(21), pp. 1713-1715 and IOVS, 2000, Vol.41(4), 545. The article of S. Patel et al in Refractive & Corneal Surgery, 1993, Vol. 9, pages 173-181 discloses the asphericity of posterior corneal surfaces. It is suggested that the corneal data can be used together with other ocular parameters to predict the power and the asphericity of an intraocular lens with the purpose of maximizing the optical performances of the future pseudophakic eye. Furthermore, it was also recently observed by Antonio Guirao and Pablo Artal in IOVS, 1999, Vol. 40(4), S535 that the shape of the cornea changes with age and becomes more spherical. These studies indicate that the cornea in the subjects provides a positive spherical aberration, which increases slightly with the age. On the other hand, the rotationally symmetric aberration of the anterior corneal surface does not seem to be different between younger and older eye according to results found by T Oshika et al in Investigative Ophthalmology and Visual Science, 1999, Vol. 40, pp. 1351-1355. In Vision Research, 1998, 38(2), pp. 209-229, A Glasser et al. investigated the spherical aberration of natural crystalline lenses from eyes obtained from an eye bank after the cornea has been removed. According to the laser scanner optical method used herein it was found that the spherical aberration from an older lens (66 years) shows positive spherical aberration, whereas a 10-year-old lens shows negative spherical aberration. In addition, Vision Research, 2001, 41, pp. 235-243 (G Smith et al) discloses that the natural crystalline lens appears to have negative spherical aberration when in the relaxed state. Smith et al suggest that because older eyes have a larger aberration, it is likely that the spherical aberration of the crystalline lens becomes less negative with age. [0011] In Ophthal. Physiol. Opt., 1991, Vol. 11, pp. 137-143 (DA Atchison) it is discussed how to reduce spherical aberrations in intraocular lenses by aspherizing the lens surface. The methods outlined by Atchison are based on geometric transferring calculations, which do not consider diffraction effects and any variations in refractive index along the ray path in inhomogeneous elements. These calculations will lead to errors close to the diffraction limit. Also in WO 98/31299 (Technomed) a ray tracing method is outlined according to which the refraction of the cornea is attempted to be considered for the design of an intraocular lens. In view of the foregoing, it is apparent that there is a need for ophthalmic lenses that are better adapted or compensated to the aberrations of the individual surfaces of the eye and are capable of better correcting aberrations other than defocus and astigmatism, as provided by conventional ophthalmic lenses. DESCRIPTION OF THE INVENTION [0012] It is an object of the invention to provide for methods that result in obtaining an ophthalmic lens, which provides the eye with reduced aberrations. [0013] It is another object of the invention to provide methods of obtaining an intraocular lens capable of reducing the aberration of the eye after its implantation into the eye. [0014] It is a further object to provide for methods of obtaining an intraocular lens capable of compensating the aberrations resulting from optical irregularities in the corneal surfaces. [0015] It is a still further object of the present invention to provide an intraocular lens which is capable of restoring a wavefront deviating from sphericity into a substantially more spherical wavefront. [0016] It is a also an object of the present invention to provide an intraocular lens which is capable of correcting for mean optical irregularities and imperfections found in a particular group of people and thereby provide a lens with improved optical performance for an individual belonging to the same group. [0017] The present invention generally relates to an ophthalmic lens and to methods of obtaining said ophthalmic lens that is capable of reducing the aberrations of the eye. By aberrations in this context is meant wavefront aberrations. This is based on the understanding that a converging wavefront must be perfectly spherical to form a point image, i.e. if a perfect image shall be formed on the retina of the eye, the wavefront having passed the optical surfaces of the eye, such as the cornea and a natural or artificial lens, must be perfectly spherical. An aberrated image will be formed if the wavefront deviates from being spherical. In this context the term nonspherical surface will refer to rotationally symmetric, asymmetric and/or irregular surfaces, i.e. all surfaces differing from a sphere. The wavefront aberrations can be expressed in mathematical terms in accordance with different approximate models as is explained in textbook references, such as M. R. Freeman, Optics, Tenth Edition, 1990. [0018] In a first embodiment, the present invention is directed to a method of designing an intraocular lens capable of reducing aberrations of the eye after its implantation. The method comprises a first step of characterizing at least one corneal surface as a mathematical model and by employing the mathematical model calculating the resulting aberrations of the corneal surface. An expression of the corneal aberrations is thereby obtained, i.e. the wavefront aberrations of a spherical wavefront having passed such a corneal surface. Dependent on the selected mathematical model different routes to calculate the corneal aberrations can be taken. Preferably, the corneal surface is characterized as a mathematical model in terms of a conoid of rotation or in terms of polynomials or a combination thereof. More preferably, the corneal surface is characterized in terms of a linear combination of polynomials. The second step of the method is to select the power of the intraocular lens, which is done according to conventional methods for the specific need of optical correction of the eye, for example the method described in U.S. Pat. No. 5,968,095 From the information of steps one and two an intraocular lens is modeled, such that a wavefront from an optical system comprising said lens and corneal model obtains reduced aberrations. The optical system considered when modeling the lens typically includes the cornea and said lens, but in the specific case it can also include other optical elements including the lenses of spectacles, or an artificial correction lens, such as a contact lens, a corneal inlay implant or an implantable correction lens depending on the individual situation. [0019] Modeling the lens involves selection of one or several lens parameters in a system which contributes to determine the lens shape of a given, pre-selected refractive power. This typically involves the selection of the anterior radius and surface shape, posterior radius and surface shape, the lens thickness and the refractive index of the lens. In practical terms, the lens modeling can be performed with data based on a conventional spherical lens, such as the CeeOn.RTM. lenses from Pharmacia Corp., as exemplified with the CeeOn.RTM. Edge (Model 911). In such a case, it is preferred to deviate as little as possible from an already clinically approved model. For this reason, it may be preferred to maintain pre-determined values of the central radii of the lens, its thickness and refractive index, while selecting a different shape of the anterior and/or posterior surface, thus providing one or both of these surfaces to have an nonspherical shape. According to an alternative of the inventive method, the spherical anterior surface of the conventional starting lens is modeled by selecting a suitable aspheric component. Preferably the lens has at least one surface described as a nonsphere or other conoid of rotation. Designing nonspherical surfaces of lenses is a well-known technique and can be performed according to different principles and the description of such surfaces is explained in more detail in our parallel Swedish Patent Application 0000611-4 to which is given reference. [0020] The inventive method can be further developed by comparing wavefront aberrations of an optical system comprising the lens and the model of the average cornea with the wavefront aberrations of the average cornea and evaluating if a sufficient reduction in wavefront aberrations is obtained. Suitable variable parameters are found among the above-mentioned physical parameters of the lens, which can be altered so as to find a lens model, which deviates sufficiently from being a spherical lens to compensate for the corneal aberrations. Continue reading... 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