Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1989-05-18
1991-10-29
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
359652, G02C 702
Patent
active
050610589
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an ophthalmic lens for use in the correction of astigmatism.
STATE OF THE ART
Ophthalmic lenses with astigmatic action usually have a spherical and a toric surface. Lenses of this kind have a number of disadvantages:
Aberrations are only optimumly corrected for the vertex of the lens, while increasing along the main sections as well as between the main sections toward the edge. In lenses of positive power, center thickness is very great and in lenses of negative power, the thickness of the edge is quite great, moreover, the edge thickness varies along the circumference of the lens due to the toricity of the lens, the latter being extremely bothersome in lenses in so-called rimless frames.
Furthermore, if there is a marked difference in sight impairment between the two eyes, the two lenses will also differ considerably in appearance.
Although aberrations may be diminished by means of aspherical main sections, by way of illustration conical sections, the reduction in thickness that can be achieved is rather minimal.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide an ophthalmic lens for use in the correction of astigmatism, in which the critical thickness, i.e. the center thickness in the case of lenses of positive power and the thickness of the edge in the case of lenses of negative power and/or the variation in the edge thickness along the circumference of the lens, is substantially reduced compared to the state of the art.
An inventive solution to the foregoing object and its further embodiments are set forth in the claims hereto:
In accordance with the present invention it was understood that a considerable reduction in the critical thickness and/or the variation of the edge thickness along the circumference of the lens can be attained by changing the refractive index in the case of plus lenses at least along the stronger refracting main section and in the case of minus lenses at least along the lower refracting main section so that at least part of the cylindrical correction is achieved by changing the refractive index. As in plus lenses, the critical thickness, that is the center thickness or the edge thickness, is determined by the higher refracting main section and in minus lenses by the (in a mathematical sense) lower refracting main section hereinafter this main section will be called the critical main section. Accordingly the other main section will be called the non-critical main section.
Of course, it is also possible within the scope of the inventive concept to change the refractive index in the direction of the other main section and/or in the direction of the optical axis of the lens in addition to changing the refractive index along the critical main section. In this manner, aberrations can be kept at a minimum over the entire ophthalmic lens.
In any event, it is, however, advantageous if the change in the refractive index along the (in a mathematical sense) lower refracting main section is mirror symmetrical to the plane of the second (non-critical) main section.
In most cases of utilization, however, the further embodiment in which the refractive index only changes along the critical main section suffices completely. Strikingly, it is not only possible to reduce the critical thickness considerably with such a simple--one-dimensional--variation of the refractive index, but it is also possible to maintain specific predetermined conditions regarding image properties and, in particular, the quantity of the aberrations along the critical main section, i.e. it is possible to maintain two or even more quantities under predetermined restrictions by changing a single parameter.
Furthermore, the one-dimensional design of the gradient of the refractive index has the advantage that it can be produced comparatively simply. Nonetheless, such a one-dimensional gradient has not hitherto been considered in the relative literature. With regard to this, reference is made to, by way of illustration, the survey "Techno
REFERENCES:
patent: 3486808 (1969-12-01), Hamblen
patent: 4856889 (1989-08-01), Guilino et al.
Altheimer Helmut
Guilino Gunther
Pfeiffer Herbert
Optische Werke G. Rodenstock
Sugarman Scott J.
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