Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2002-05-28
2004-07-20
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
Reexamination Certificate
active
06764179
ABSTRACT:
INCORPORATED BY REFERENCE
The disclosure of Japanese Patent Application No. 2001-159654 filed on May 28, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel method of designing ophthalmic lenses including a contact lens, an intraocular lens and a spectacle lens, which permits a high-precise and quick design of a lens shape capable of providing a desired refractive power. The present invention relates also to an ophthalmic lens provided according to this method.
2. Description of the Related Art
Conventionally, contact lenses, intraocular lenses, spectacle lenses, and various other ophthalmic lenses have been provided in order to correct or otherwise improve the refractive abnormalities of the human eyes. An important issue concerning these lenses is to precisely establish a refractive power needed for the eyes worn with these lenses.
An refractive power of an ophthalmic lens can basically be obtained according to known equations based on Snell's Law, while taking into account of configurations of the front and back surfaces of the lens, lens thickness, and the refractive index of the lens material.
However, an inherent problem of optical lenses, i e., effects of aberrations makes it practically impossible to provide a desired refractive power to every light rays passing through the various points on a lens. When the lens is designed and shaped on the basis of a specific refractive power existing at a certain point on the lens surface, the lens is very likely to fail in providing the desired refractive with consideration for the total range of the optical zone.
In practical cases of single-focus ophthalmic lenses for correcting myopia, hyperopia, and the like, for example, a front and a back lens surface are usually provided with a spherical shape having a single radius of curvature. This arrangement may cause significant spherical aberration, particularly when such a single-focus ophthalmic lens has high refractive power. This makes it difficult to obtain the desired refractive power with high accuracy. In multifocal lenses for presbyopia and the like, a plurality of concentric or otherwise structured segmented optical areas may be formed inside the optical zone. Such a multifocal lens is provided with a complex surface configuration in which surfaces of the segmented optical areas have spherical shapes with mutually different radii of curvature. This complex surface configuration of the multifocal lens causes an increase of spherical aberration as viewed over the entire range of the optical zone, and generates interference between the segmented optical areas that makes it more difficult to stably obtain the desired refractive power as long as the plurality of segmented optical areas are considered together. As to contact lenses, typical tendency in designing back surfaces of the lenses affects both single-focus and multifocal lenses. Namely, the back surface of a contact lens is generally provided with a relatively small radius of curvature in conformity with a cornea of a wearer, whereby the effect of spherical aberration becomes even more significant, making it difficult to obtain the desired refractive power with high precision in the entire optical zone.
To cope with these drawbacks, one method has been proposed wherein ray tracing is performed at numerous points in the optical zone to trace and analyze paths of light rays through the optical zone, and an optimal lens surface configuration is designed on the basis of analysis results to accurately establish the desired refractive power, for example. However, this method requires complex and time-consuming calculations for analyzing the paths of the light rays at the numerous points by the ray tracing, and suffers from difficulty in determining the overall configuration of the lens surface on the basis of the mutually independent analysis results obtained for the numerous points in the optical zone, as well. Therefore, the proposed method is not always effective.
Another method has also been proposed wherein MTF (modulation transfer function) is used to evaluate the effect of aberration in an ophthalmic lens whose shape is designed on the basis of general optical equations derived from Snell's Laws. However, such a conventional method merely involves a use of MTF as a simple aberration evaluation means, and fails to propose an effective design method to provide ophthalmic lenses capable of generating desired refractive powers.
SUMMARY OF THE INVENTION
It is therefore one object of this invention to provide a novel method of designing an ophthalmic lens in which a desired refractive power is given to an optical zone of the lens with ease and high precision, while taking into account of the effect of aberration.
It is another object of this invention to provide an ophthalmic lens whose optical zone is designed to provide a desired refractive power with high precision.
The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A method of designing an ophthalmic lens comprising the steps of: (a) defining a preliminary lens shape by preliminary determining a shape of the ophthalmic lens; and (b) varying the preliminary lens shape so as to adjust a peak position of MTF in relation to an image surface distance concerning the preliminary lens shape such that the peak position of the MTF conforms to a desired focal length of the ophthalmic lens.
According to the method of this mode of the invention, Modulation Transfer Function or MTF can be used as an index of an actual refractive power, and the preliminary lens shape is varied on the basis of the MTF measurements so as to establish a desired refractive power of the ophthalmic lens. This is unlike conventional lens design method wherein the MTF is simply utilized as a measure for evaluating aberrations. Described in detail, the present method utilizes MTF data computed concerning the preliminary lens shape, and detects an image distance or an image surface position where the MTF has a peak value. This image surface position is referred to as the “peak position of the MTF”. An attention paid to the difference in distance between the peak position of the MTF (i.e., the image surface distance) and a desired focal position (i e., the desired focal length) of the ophthalmic lens has revealed that the difference between these distances provides indexes in the form of direction and magnitude, which are useful for varying the preliminary lens shape desirably. That is, the present method has been developed on the basis of a novel technical finding and concept that varying of the preliminary lens shape on the basis of these indexes makes it possible to define the desired refractive power of the ophthalmic lens with high accuracy. In the present method, accordingly, the peak position of the MTF is finally equal to the desired focal position, i.e., the desired focal length, thereby establishing an excellent actual refractive power of an obtained ophthalmic lens with high accuracy. As well known in the art, MTF describes the reduction in contrast of a pattern of lines, black and white, arranged at regular intervals, which is imaged through a lens. The MTF is given as a function of a spatial frequency, and is usually demonstrated on a graph in which the
Oyama Yoshihiko
Sakai Yukihisa
Beyer Weaver & Thomas LLP
Collins Darryl J.
Menicon Co. Ltd.
Sugarman Scott J.
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