Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2002-04-10
2004-12-14
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S16000R, C351S16000R, C351S177000, C623S006310
Reexamination Certificate
active
06830332
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ophthalmic lens comprising a diffractive part.
Furthermore it relates to a method for designing said ophthalmic lenses.
BACKGROUND OF THE INVENTION
A wavefront passing the eye will be influenced by the optical parts of the eye such that for example chromatic aberration is provided to the wavefront. The reason is that the refractive indices of the materials in the optical parts of the eye differ for different wavelengths. Thus light having different wavelengths will be refracted a different amount and they will fall on the retina at different places, i.e. different colors can not be focused to the same point. This is called chromatic aberration.
Recently there has been much interest in the correction of the monochromatic aberrations of the eye. It has been revealed that when all monochromatic aberrations are corrected in the human visual system, it serves to unmask the chromatic aberration of the eye. Therefore, in order to optimize the optical quality of the eye, a combination of monochromatic and chromatic aberrations needs to be corrected. A diffractive pattern could be configured to provide a passing wavefront with chromatic aberration of the opposite sign as chromatic aberration from the eye. Thus a diffractive pattern can be used to correct for chromatic aberration introduced to a wavefront from the optical parts of the eye. Some background theory of chromatic aberration can be found in, for example Chapter 17 in “Optics of the Human Eye” written by David A. Atchison and George Smith. A theoretical background of the diffractive pattern could be found in the article “Practical design of a bifocal hologram contact lens or intraocular lens”, Allen L. Cohen, Applied Optics 31(19)(1992). Ophthalmic lenses, which on at least one surface comprises a diffractive pattern for correcting for chromatic aberration are known from for example U.S. Pat. Nos. 5,895,422, 5,117,306 and 5,895,422. These lenses do, however not, compensate for other aberrations provided by the eye surfaces. In SE 0001925-7, and WO 01/89424, aspheric lenses are designed to compensate for spherical aberration. In some applications these lenses will provide the eye with an increase in chromatic aberration. It is therefor a need of an ophthalmic lens for correcting refractive errors that also can correct for monochromatic and chromatic aberrations.
DESCRIPTION OF THE INVENTION
An object of the present invention is to improve the visual quality for a patient.
A further object of the present invention is to provide an ophthalmic lens, which corrects for chromatic aberration and at least one type of monochromatic aberration.
A further object of the present invention is to provide an ophthalmic lens, which corrects for both chromatic and spherical aberration.
Still a further object of the invention is to correct for spherical aberration as expressed by the 11
th
normalized Zernike term.
A yet further object is to provide an aspheric lens capable of correcting for spherical aberration having a diffractive part adding refractive power to the lens and providing compensation for chromatic aberration introduced by the optical surfaces of the eye and by the aspheric lens surface. In this text the term aspheric will refer to rotationally symmetric, asymmetric and/or irregular surfaces, i.e. all surfaces differing from a sphere.
These objects are achieved by an ophthalmic lens as initially described in “technical field of invention”, which according to the invention further comprises a refractive part comprising at least one surface, which is configured to compensate a passing wavefront at least partly for at least one type of monochromatic aberration introduced by at least one of the optical parts of the eye. The diffractive part is according to the invention capable of compensating a passing wavefront at least partly for chromatic aberration introduced by at least one of the optical parts of the eye. Said refractive and diffractive parts together contribute to a required power of the lens. In this text “the optical parts of the eye” refer to the parts of the eye that contribute to the refraction of incoming light. The cornea of the eye and the natural or an implanted lens are optical parts of the eye. But also inhomogeneities, e.g. in the vitreous are considered as the optical parts of the eye. An optical element that combines both diffractive and refractive optics is called a hybrid element. The monochromatic aberration could be for example astigmatism, coma, spherical aberration, trifoil, tetrafoil or higher aberration terms.
Hereby an ophthalmic lens is achieved that is capable of compensating for at least one type of monochromatic aberration and for chromatic aberration introduced by the optical parts of the eye to a passing wavefront.
Preferably the diffractive part also is capable of compensating a passing wavefront at least partly for chromatic aberration introduced by the refractive part of the lens.
In one embodiment of the invention the monochromatic aberration corrected for is spherical aberration.
The longitudinal chromatic aberration of the eye is very well understood and has been shown to have very similar values from subject to subject (Thibos et. al., “The chromatic eye: a new reduced heye model of ocular chromatic aberration in humans”, Applied Optic, 31, 3594-3600, (1992)). It has also been shown to be stable with age (Mordi et. al., “Influence of age on chromatic aberration of the human eye”, Amer. J. Optom. Physiol. Opt., 62, 864-869 (1985)). Hereby an ophthalmic lens to correct for the average chromatic aberration of the eye could be designed.
Diffractive surfaces can be characterised by their so called phase functions. This phase function describes the additional phase that is added to a ray when it passes the diffractive surface. This additional phase is dependent on the radius of the lens where the ray strikes the surface. For radially symmetric diffractive surfaces this function can be described using Equation 1.
φ
(
r
)
=
2
π
λ
(
DFO
+
DF1r
+
DF2r
2
+
DF3r
3
+
DF4r
4
+
…
)
(
1
)
Where r is the radial coordinate, &lgr; the wavelength and DF0, DF1 etc. are the coefficients of the polynomial.
The diffractive part of the lens can also introduce some spherical aberration to a passing wavefront. Preferably, according to the present invention, the refractive part is made capable to compensate a passing wavefront for the spherical aberration introduced by the diffractive part of the lens. Hereby, the spherical aberration could be reduced to a minimum after the wavefront has passed the optical parts of the eye and said lens.
To compensate for the spherical aberration, an aspherical surface, with a lateral height described by Equation 2, could be introduced to the refractive part of the lens. An aspheric surface can be configured to counteract the spherical aberration introduced by the optical parts of the eye and by the diffractive part of the lens. All the optical parts of the eye do not necessarily have to be considered. In one embodiment it is sufficient to measure the spherical aberration introduced by the cornea of the eye and compensate for only the spherical aberration provided by the cornea and optionally also for the spherical aberration introduced by the diffractive part of the lens. For example Zernike terms could be used to describe the optical surfaces of the eye and thus also be used to configure the aspheric surface of the lens, which is adapted to compensate for the spherical aberration. Table 1 shows the first 15 normalized Zernike terms and the aberrations each term signifies. The spherical aberration is the 11
th
normalized Zernike term. The designing of a lens that is adapted to compensate for aberrations as expressed in Zernike terms is explained in further detail in the Swedish patent application SE 0000614-4 to which is given reference.
z
=
(
1
R
)
*
r
2
1
+
1
-
(
1
R
)
2
(
cc
+
1
)
r
2
+
ADr
4
+
AEr
6
(
2
)
Where R is the radal coordinate of the lens, cc
Piers Patricia Ann
Weeber Hendrik Albert
Advanced Medical Optics, Inc.
Gluck Peter Jon
Kozlowski Holly
Sugarman Scott J.
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