Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2000-06-16
2002-06-25
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C623S006240
Reexamination Certificate
active
06409339
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a multifocal lens, having a reading part in the bottom part and another lens in the top part. This lens can be a hard or soft contact lens as well as an intra ocular lens.
BACKGROUND OF THE INVENTION
A multifocal lens is known from U.S. Pat. No. 4,854,089. In the general prior art it is known to provide a part with smaller radius of curvature in the centre of the lens. This part with smaller radius of curvature is, as it were, placed on a larger part with a larger radius of curvature. This is a rotationally symmetrical lens where there is no need for stabilizing means. Due to the fact that there is a kink at the position of the R
lecs
-R
verte
(reading-distance) transition, a great deal of reflection occurs in the direction of the optical axis, which means that the optical characteristics of this lens are inadequate.
Designs are also known from the prior art in which a reading part is moulded or cast into the lens material, or is disposed on the front side in a half moon shape. Such systems can work only if the lens can move fully from distant to close up. The reading part covers about 50% of the pupil if the lens is centred on the cornea. In order to obtain an undistorted image, the lens will have to move downwards until it is at or below the lower eyelid. The lens has to move up again for reading. These systems are characterized in that the optical axes do not lie level, with the result that an image discontinuity always occurs. This causes an unsteady image for the wearer, and leads to complaints of double vision and shadow images.
In another system (tangent streak) the optical axis does remain level. It lies precisely in the centre of the lens. The disadvantage of this lens is that the distance/close-up division is always 50%. The lens is divided exactly into two halves. This optical system is characterized in that the two outer radii for the reading and distance part are monocurved, i.e. they are spherical from the centre to the edge. This produces a very thick lens. This design also means that at the edge quite a large height difference arises between the two curves. Both have a very negative influence on wearing and vision comfort.
On the other hand, the reading part on the lens is designed as a sort of half moon. The characteristic feature of this lens is the enormous image discontinuity which occurs. The reason for this lies in the fact that the lens has to be prismatic, in order to obtain a stable position on the eye, on the one hand, and in order to leave sufficient material to be able to make the reading part, on the other hand, This prismatic effect is present optically in the distance part. However, the reading part is not provided in the second instance with prism effect. The optical centre points do not lie on the optical axis, nor can they be joined tangentially in the centre. A further disadvantage is that the shape of the ‘half moon’ on the front side, which is the reading part, is not adjustable. This is a resultant. The dimensions of this part are different in the case of each lens power combination, with the result that much too large a reading part and too small a distance zone are produced. The consequence is that this lens has many reflections for the user. The lens requires a great vertical movement in order to function. This causes a high degree of discomfort for the user.
It is therefore the object of the present invention to provide a multifocal lens which has bivisual features, without the presence of a kink or similar transition which causes troublesome reflections in the direction of the optical axis or an image discontinuity, and which lens has such features that no great movement on the cornea is needed for fulfilment of the distance and reading functions.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a multifocal lens is provided with a reading portion in the lower lens part and another lens portion in its upper part, wherein the reading portion comprises a recess which is bounded on all sides by the remaining lens part, and in that the outer limit of the reading portion lies on or within an imaginary sphere having its origin and radius of curvature coinciding with the radius R
v
of said other lens portion.
The reading part is taken from the remaining part of the lens, i.e. instead of the lens being provided with a thickening for the reading part, it is provided with a thinner part or recess. This means that an extremely gradual transition between reading and distance part can be provided, with the result that irritation, image discontinuity and reflection are avoided. The lens need not move any more than an ordinary monofocal lens, because the distance/close-up ratio in the lens system can be selected in the optimum way. A ratio with 30-40% reading part and 60-70% distance part is a good value. In some cases where lenses are in a low position on the eye, another ratio, for example 50% reading and 50% distance, can give a better solution. The size and position and shape of the zones can be tailored exactly by the invention to the needs of the lens wearer. There is no transition in the centre of the lens because the two curves merge into each other at the position of the transition, i.e. the angle at which the two curves touch each other is the same. The height difference at a occurring further position in the surface is reduced sinusoidally without an optically appreciable effect, or is reduced in such a way that optically an effectively working intermediate zone is produced. An optically working transition zone is then produced between sectors with multifocal effect. This means that a lens can be made extremely thin, so that the oxygen permeability of the lens is also optimal. At the outer periphery of the lens, it will have the dimensions of the remaining part of the lens surface, i.e. there will be a transition zone between the outer periphery of the lens and the reading part. Irritation is avoided in this way.
According to a further aspect of the invention, provision is made for a multifocal lens which is provided with a reading part in the usual way at the bottom side. According to an further aspect of the invention, at least one additional reading part, which is disposed opposite (relative to the axis of the lens) the first reading part is provided. This means that the stabilization of the lens is less critical, or may even be superfluous. This additional reading part can have the same power as or a different power from the first reading part.
Location of the lens is of course of importance. In a contact lens to that end stabilisations means are provided. According to a further aspect of the invention, the lens does comprise an intra ocular lens which is positioned through locating means in the lens cavity of the eye.
Such a lens is preferably provided with the position-stabilizing means to be described below, but it must be understood that it is also possible to work with other position-stabilizing means known in the prior art. It has been found that the human eye becomes accustomed to the presence of such a second reading part, so that the position of the lens on the eye becomes less critical.
Both the reading part and the distance part are preferably symmetrical relative to the vertical axis of the lens in the use position Moreover, a transition zone, comprising 10-30% of the surface area of the distance part, is preferably present between the reading part and the distance part.
The position-stabilizing means described above can comprise any designs known in the art. With bifocal lenses and other lenses which are not rotationally symmetrical, it is important in some way to fix the position of such a lens on the cornea. In the abovementioned European patent application it is proposed that elevations should be disposed on the horizontal axis of symmetry. This achieves stabilization each time that the eyelids are closed. The height of such elevations relative to the remaining part of the lens lies between 0.1 and 0.2 mm.
The condition for proper functioning of such
Handal & Morofsky
Procornea Holdings B.V.
Sugarman Scott J.
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