Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-06-21
2004-03-30
Schwartz, Jordan M. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S177000
Reexamination Certificate
active
06712467
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a progressive-power lens (progressive multifocal lens) for use in spectacles for both near and far use, and more particularly to a progressive-power lens affording comfortable wear even when the curve of the lens is shallow, and to a design process therefor.
BACKGROUND ART
Spectacles with progressive-power lenses that function as spectacles for both near and far use are used in cases where the ability of the eyes to adjust has diminished due to presbyopia, for example. A progressive-power lens comprises an upper far zone for distance vision and a lower near zone for near vision. The intermediate portion between the far zone and near zone is for intermediate vision.
Typically, of the two faces, namely front and back faces of a progressive-power lens, the front face, directed towards objects, is the progressive face on which the refractive power (hereinbelow, refractive power is occasionally referred to as “power”) changes progressively, and the back face, directed towards the eyes, is of relatively simple prescription, for example, spherical or astigmatic. The surface refractive power of the distance portion on the progressive face is termed the “base curve” and is used as a reference face when designing the progressive face. Accordingly, progressive faces with substantially identical progressive characteristics can be obtained with different base curves, at least insofar as surface refractive power is concerned. Typically, a deeper base curve (i.e., a smaller radius of curvature on the curving face) is associated with greater center thickness in a (+) lens, or with greater edge thickness in a (−) lens. Conversely, a shallower base curve allows the lens to be made thinner, but presents certain disadvantages in terms of power (transmission power) and aberration (transmission aberration).
When the eye travels from a visual target at infinite distance ahead to a visual target closer ahead, wearing these spectacles, a continuous line of the set of points of intersection of the line of vision with the lens can be assumed. This line is typically termed the “principal sight line,” “principal meridonal line,” or “center reference line,” It is a line that extends vertically through the center of the lens so as to divide it into substantially left and right portions; of the front and back faces of the lens, the line is defined on the progressive face where progressive action is present.
The assessment of a progressive-power lens is typically performed in terms of analysis of the level of error in refractive power and/or the level of astigmatism along the principal sight line, as well as the refractive power error distribution and astigmatism distribution in the zones to the left and right of the principal sight line, etc. The criteria for conventional evaluation generally dictate that astigmatism on the principal sight line be zero. That is, there is a series of minute spherical faces on the principal sight line; such a principal sight line is sometimes termed a “umbilical curvature.”
Even if it is possible to eliminate the refractive power error or astigmatism of a spectacle lens per se in an ideal manner, this will not necessarily make it possible to eliminate aberrations such as astigmatism, curvature of field, etc., which are caused in an image produced in the eye when the spectacle lens is worn. It is assumed that the quality of sight which is obtained by wearing spectacles is determined, after all, by such aberrations of the intraocular and not solely by the optical characteristics of the lens surface. In other words, aberrations in intraocular image and the like are also affected by various factors including the position on the lens through which the line of sight passes, the distance from the lens to the center of rotation of the eye, the refractive power of the ocular lens, and the angle of rotation of the eye. Accordingly, there will be cases when, even if the astigmatism on the lens surface is zero, the astigmatism of the intraocular image obtained when the lens is worn will not be zero. Conversely, it will also be found that, when attempts are made to obtain zero aberration of intraocular image, the astigmatism on the lens surface will assume a value other than zero.
Japanese Patent Publication S47-23943 discloses a method for improving astigmatism and aberration (e.g., curvature of field, distortion, etc.) in distance vision, intermediate vision, and near vision with spectacle wear. Where the correction affording the improvement is implemented on the progressive face, surface astigmatism along the principal sight line on the progressive face is not zero; in other words, this progressive-power lens has a so-called “non-umbilical curvature” portion.
In Japanese Patent Applications Laid-Open (JP-A) S56-78817, Japanese PCT Patent Application Laid-Open H4-500870, JP-A H6-18823, JP-A H8-136868, Patent Application S57-170627 and the four divisional applications thereof, and elsewhere are disclosed inventions purporting to improve astigmatism during spectacle wear.
These publications suggest that, when the surface curve of a spectacle lens is designed, it is necessary to take into consideration the astigmatism of intraocular image, etc. observed when spectacles are worn. However, research carried out by the inventors of the present invention has shown that the plurality of error factors such as astigmatism, etc. occurring with spectacle wear include factors which cancel each other out, and that good results cannot be obtained through the simple approach of minimizing the respective error factors.
With respect to this point, during wear of the aforementioned progressive-power lens, where the intraocular image of an object point viewed through an arbitrary location on the spectacle lens is not focused at a single point, but rather imaged as two line segments separated by an interval, let the difference of the two refractive powers for these two focal locations be defined as transmission astigmatism at the aforesaid location on the spectacle lens; and let the difference between the average value of refractive powers for the two focal locations and the refractive power for the correct focal location be defined as the transmission average refractive power error (curvature of field). Where correction is performed, for example, so as to simply minimize the astigmatism in intraocular image (i.e., transmission astigmatism) in the principal zone of the lens, or at least in the principal zone on the principal sight line, the error resulting from focusing of the image at a location diverging from the correct focal location in the eye (i.e., transmission average refractive power error) will increase, and this will often result in decreasing the wear comfort.
Accordingly, it is important, when designing a lens, to consider the balance between the astigmatism and the transmission average refractive power error. However, it has been found that an ideal balance cannot be achieved by such a simple approach as to make these two equivalent in the principal zone of the lens. Particularly where a shallow base curve is employed in order to make the lens lighter and thinner, the distance between the eye and the distance portion increases, as does the angle of the normal between the visual axis and the lens face, resulting in a marked increase in transmission astigmatism and the transmission average refractive power error. Accordingly, greater correction is required, and this correction has the drawback of creating side effects that can in turn cause aberration to increase.
The present invention was developed with the foregoing in view, and has as an object to provide a progressive-power lens affording superior wear comfort, even where a shallow base curve is employed in order to make the lens lighter and thinner, and a design method for such a lens.
DISCLOSURE OF THE INVENTION
To solve the aforementioned problems, the first invention is a progressive-power lens comprising a distance portion formed in the upper region of the lens; a near portion f
Hoya Corporation
Oliff & Berridg,e PLC
Schwartz Jordan M.
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