Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1990-11-23
1993-05-25
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
351177, G02C 704
Patent
active
052144534
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns contact lenses adapted to ensure correction, through a single dioptric means, for both visual defects related to far range vision (miopia and hypermetropia), and visual defects related to near range vision (presbyopia).
Furthermore, this invention concerns the process for manufacturing said contact lenses, through use of any type of lathe, both numerically controlled and "duplicating" lathe, controlled by a computer or electronic data processing equipment, according to special process computer programs. As it is already known, in the lenses for conventional glasses, the possibility to see correctly both in the near distance range and in the far distance range, is provided by dividing said lenses in two parts, wherein the upper part enables far range vision while the lower part enables near range vision, owing to the eye motions relative to the lens. Therefore, said lenses are called bifocal lenses. Also known are trifocal and multifocal lenses, both with visible or invisible edge. As it should be apparent, this type of lens partitioning in two or more asymmetrical parts is not feasable in contact lenses, since the lens constantly follows the eye motions, and no relative displacements are possible. While striving to overcome said drawback with contact lenses, a compromise has been made, trying to exploit the capacity of the pupil to adapt to the different light conditions. Therefore, it has been contrived to divide the contact lens in two or more concentric areas having a different degree of spherical curvature, whereby the pupil, when expanding or contracting, can use the different areas, according to the light available, while being supported in this process by the discrimination and synthesis capacity of the brain. However, it has been noticed that said lenses having areas with different spherical curvature gave a blurred vision (for instance split vision) and the eye got easily tired.
SUMMARY OF THE INVENTION
The object of this invention is to overcome the above drawbacks by providing contact lenses based on the inventive concept that the central spherical area is designed to provide a perfect far range vision in any light condition, and an optimum near range correction by utilizing the single or plural immediately adjacent concentric areas, having non-spherical progressive curvature. A further important feature of the contact lenses according to this invention is the fact that all corrections are obtained by suitable machining operations of the lens outer surface, both in the neutral and in the positive and negative lenses.
The near range vision correction mechanism is based on the development of at least an external curve whose dioptric power progressively changes while proceeding in a radial direction from the inside to the outside, said difference in dioptric power from the innermost to the outermost point of the area taken into consideration being given by the algebraic sum of the diopters referred to the two visual defects. The term "progressive" is used herein to indicate that the lens outer surface curvature changes according to a perfect linear progression between the two end values. Said geometrical pattern is obtained by progressively reducing the outer radius, starting from the central spherical area, at a progressive rate and such as to obtain the sagittal of the curve provided for near range correction. The higher is the difference between the far range correction and the near range correction, the faster will be the progression. This type of contact lens may be manufactured by means of numerically controlled lathes, or "duplicating lathes" of any model, and may be applied to any type of material, both hard and soft.
For the purpose of making this invention more easily understood, some definitions of terms currently used in the art of contact lenses. The definition "base radius" means the radius of the spherical surface facing the eye; the term "sagittal" means the base depth; "optical area" means the diameter of the lens area assigne
REFERENCES:
patent: 4580882 (1986-04-01), Nuchman et al.
Hanrath James P.
Sugarman Scott J.
Vigil Thomas R.
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