MULTIFOCAL CONTACT LENSES

Abstract: A multifocal contact lens (1) provides zones each of differing focal characteristics each zone (N) and (F) extending radially. The zones (N) and (F) comprise segments radially extending from a common centre (C) with adjacent segments defining different radial curvatures of the surface of thelens producing different focal characteristics. In a preferred construction the zones as seen in sideprofile have a sinuous form with the adjacent zones smoothly blending into one another.

Description: Multifocal contact lenses. This invention relates to multifocal contact lenses which have the ability to provide simultaneous near and distance vision to a wearer by projecting two images onto the retina, which images blend into each other. Such lenses may be of rigid or of soft material. In a known construction the lens comprises a series of concentric rings each ring zone producing an area having different focal length. A disadvantage of this construction is that operation differs according to the diameter of the iris at any one time and thus significant changes occur according to the ambient light. An object of this invention is to provide a multifocal contact lens which reduces the disadvantages of the known types. A further object is to provide a contact lens which provides a more continuous focus to the eye. According to this invention there is provided a multifocal contact lens, the surface of the lens providing zones each of differing focal characteristics, characterised in that each said zone extends radially. In a preferred construction the zones comprise radially extending segments, adjacent segments having differing focal characteristics achieved by a different surface curvature. Advantageously the adjacent zones blend smoothly or steplessly together, preferably through curved transition zones. In one construction, a section through a mid point between the centre of the lens and the periphery and which section extends concentrically about the centre axis has a sinuous profile. The advantage is that each zone blends into the next giving a continuous focus to the eye. Further and preferred features of this invention will now be described with reference to the drawings showing embodiments by way of examples. In the drawings: Fig. 1 shows in perspective view the front surface of a contact lens according to this invention, Fig. 2 shows a detail view of the edge of the lens of Fig. 1 , Fig. 3 shows a plan view of a second embodiment of lens with twelve radial segments, Fig. 4 shows a side elevation looking in the direction IV of the lens of Fig. 3, and Fig. 5 shows a section on V-V of the lens of Fig. 3, Figs. 1 and 2 show one embodiment of a lens according to this invention as example. The lens 1 is of any conventional material and is divided into a number of adjacent radially extending segments F and N. The segments F define a curvature in the radial direction from the centre C to the edge of the lens with a characteristic for far vision requirements and the segments N define a curvature in the radial direction from the centre C to the edge of the lens with a characteristic for near vision requirements. In other words the peaks F define a surface of the lens with a lesser curvature than the surface defined by the troughs N. Fig 2 shows a detail of the edge portion of the lens and as may be seen the transitions between the zones blend with a smooth curvature. All the segments merge to a common point at the centre C. It may be seen that the construction according to this invention is suitable for any size pupil and will work equally well whether the pupil is enlarged or reduced due to ambient light. The arrangement provides a radial configuration for each segment defining the lens surface curvature. The adjacent segments may blend into one another smoothly through a curve and in a stepless manner or abruptly through a step. The lens also provides infinite variability, by increasing the power on either the near or far zones; by enlarging or reducing either the near or far zones or by increasing or reducing the number of zones totally or in relation to each other. The lens may be produced using a lathing technique on a conventional contact lens manufacturing lathe but with a oscillating reciprocating tool head post on a radius attachment to give the varying curvatures as shown on the front surface. Figs. 3 to 5 show a further embodiment having twelve radial segments. The radial zones are wider and blend together with a wave-like profile as shown in Fig 4 with a thicker apex F and a thinner trough N. Each adjacent segment is thus thinner in one part and thicker in another part. In this lens a wearer would thus see, through the lens, for distance and near simultaneously as is the case when optical correction is not required. The number of radial segments provided may be as few as four and as many as desired, theoretically infinite, although there will clearly be a practical limit. This invention thus provides a multifocal contact lens (1) with zones each of differing focal characteristics each zone (N) and (F) extending radially. The zones (N) and (F) comprise segments radially extending from a common centre (C) with adjacent segments defining different radial curvatures of the surface of the lens producing different focal characteristics. In a preferred construction the zones as seen in side profile have a sinuous form with the adjacent zones smoothly blending into one another.

Claims: Claims: 1. A multifocal contact lens wherein the surface of the lens provides zones each of differing focal characteristics, characterised in that each said zone extends radially. 2. A multifocal contact lens according to claim 1 , characterised in that the zones comprise radially extending segments, adjacent segments defining different radial curvatures of the lens producing different focal characteristics. 3. A multifocal contact lens according to claim 1 or 2, characterised in that the adjacent zones blend smoothly or steplessfy together in a circumferential direction 4. A multifocal contact lens according to claim 3, characterised in that the adjacent zones blend together through curved transition zones. 5. A multifocal contact lens according to any preceding claim, characterised in that a section through a mid point between the centre of the lens and the periphery and which section extends concentrically about the centre axis has a sinuous profile. 6. A multifocal contact lens according to any preceding claim, characterised in that the number of segments is four or more 7. A multifocal contact lens according to any preceding claim, characterised in that adjacent segments have different widths. 8. A multifocal contact lens according to any preceding claim, characterised in that the peak defined by a segment has width and/or a curvature which differs from that of a trough. 9. A multifocal contact lens according to any preceding claim produced by a method using a lathing technique on a conventional contact lens manufacturing lathe but with a oscillating reciprocating tool head post on a radius attachment to give the varying curvatures as shown on the front surface. 10. A multifocal contact lens as described herein and illustrated with reference to the drawings.

Inventors: CANTOR BRIAN DAVID, CANTOR, BRIAN, DAVID
Applicants: CANTOR BRIAN DAVID, CANTOR, BRIAN, DAVID
Application year: 2001
Main classification: G02C7
IPC codes: G02C7