Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1990-10-02
1992-06-30
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 704
Patent
active
051257289
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to contact lenses and in particular relates to a new design for spherical and toric lenses whereby in addition to designing the front surface of a lens the back surface of a lens may be designed for distance correction without compromise to the comfort of the wearer.
BACKGROUND OF THE INVENTION
In the past, soft contact lenses have been designed according to the corneal shape to afford maximum stability, fit and comfort for the wearer such that there is an optimum relationship between the corneal and/or scleral profiles and the back surface of the contact lens. The comfort has generally been achieved by not designing the back surface of a lens. Thus, correcting refractive error has been achieved by designing the front surface of the lens only.
The only exception to this design philosophy has been one form or another of back surface bifocal. This type of lens is of a specific nature and is designed only to correct presbyopia (a condition whereby the eye has some loss or reduction in its power of accommodation). Hence a lens can be made with two or more focal lengths by adding a number of curves to the back or front surfaces on the lens.
Designing contact lenses primarily by back surface comfort criteria has a number of attendant disadvantages which arise with the aim to gain close proximity between the lens and the corneal/scleral profile. One disadvantage is that all refractive error must be corrected from the front surface geometry alone, thus restricting the designer in his/her choice of anterior topography.
Also lens thickness is increased peripherally as the lens power increases. Designers can reduce the front optic zone to a certain extent in order to offset this unwanted thickness somewhat, but they are limited to how small they can go.
Furthermore in back surface toric designs the extension of the toricity out to or towards the circumference of the lens will result in thick and thin areas throughout the lens. This can result in uneven lid forces being exerted on the lens during the blinking phase and cause lens rotation.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the aforesaid disadvantages of the prior art lenses by providing a contact lens, either spherical or toroidal, which is designed with both back and front surface geometry thereby allowing greater design versatility in correcting the refractive error in the eye but without compromising a close comfortable proximity between the lens and the eye of the wearer.
It is one object of the present invention to provide a back lens surface which satisfies the comfort and fit criteria and allows an arbitrary amount of refractive correction of the eye whereby the amount of refractive correction is independent of the topography of the eye.
Due to the facility for re-design of the back surface of the lens the enabled anterior format of the toric lens design is such that the traditional prism or wedge forms normally used to locate the lens' axis stability have been rendered obsolete. There is now provided a front surface design versatility enabled by virtue of the unique back surface format which allows a predetermined front optic junction thickness. The new design versatility in the lens of the present invention has created a number of significant advantages over the prior art lens designs.
Firstly, the lens thickness can be kept to a minimum by relieving the front surface geometry of handling all of the refractive error on its own.
Toric lenses can now be manufactured with an absolutely spherical periphery, thus affording the lids an even surface upon which to blink. This, now, affords the designer an enormous advantage in stabilizing the lens during the blinking phase. If used, any prisms, or wedges used for stabilizing the lens, will have a far more even effect on the lids than previous designs have allowed.
Furthermore, the present invention allows a large range of toric parameters to be covered from a small, concise base stock unit. This type of stock unit is only possible with a toric base de
REFERENCES:
patent: 4256369 (1981-03-01), Wichterle
patent: 4508436 (1985-04-01), Sitterle
patent: 4549794 (1985-10-01), Loshaek et al.
patent: 4573774 (1986-03-01), Sitterle
Newman Steve
Noack Don
Igel International Limited
Sugarman Scott J.
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