Multifocal multizone diffractive ophthalmic lenses

The present invention relates to multifocal vision correction lenses and more specifically relates to bifocal lenses having at least one diffractive zone which is added to the basic refractive power of the lens.

BACKGROUND OF THE INVENTION

Ophthalmic lenses that have two or more distinct focal lengths are known. Such lenses have been used in the past as contact lenses that are placed on the surface of the eye, or as surgically implanted intraocular lenses (IOLs) to replace the lens of the natural lens after its removal, for example in cataract surgery. Diffractive lenses are well known in the field of optics in general, but have still been little used as intraocular lenses or contact lenses. Thus, while numerous co-ops for multifocal optics have been presented for use in contact and intraocular lenses, few practices have been considered in any way.

<img file="PT97656A_D0001.tif" />

Refraction-only lenses have already been presented. For example, US Patent 4,636,211, to Nielsen et al., Discloses a bifocal intraocular lens that has concentric oriented near vision and refractive distant vision, with the eentral zone being adapted. for near vision and surrounded by a coaxial zone for far vision · The lens presented has a flat-convex or biconvex shape · US Patent 4,813,955, Aehatz et al. discloses a multifocal intraocular artificial ophthalmic lens divided into zones for short and long distance viewing, symmetrically arranged around the lens axis, which uses the refractive power of the lens material and its shape to obtain bifocal vision.

Bifocal lens designs which are based solely on the refractive properties of Fresnel lenses are also known. For example, Cohen US 4,162,122, discloses a bifocal zone contact lens consisting of a non-spherical or concave back surface. spherical shape and a continuous anterior surface which is divided into concentric annular rings which are inclined alternately with respect to the epic axis, corresponding to appropriate curvatures for near and far vision foci · Annular zone interfaces are continuous and do not create any steps or heights on the anterior surface. Each zone consists of only one refractive element, the zones forming a smooth anterior surface.

Also known are lenses which use combined properties of Fresnel lenses and Zone Fresnel plates and which are based on their diffractive effect. Cohen US Patent 4 210 391, discloses multifocal epic lenses having their multifocal properties distributed throughout the entire lens · The presented lenses share the incident light between the focal points using a zone plate and dividing the incident light into discrete beams *, each directed to a particular focal point. The beta design utilizes both Fresnel lens and Fresnel zone plate elements, based on the fact that such epic elements consist of rings or concentric zones, thus providing designs of the lens with reduced diffractive and chromatic aberrations. US Patent 4,338,005 to Cohen also discloses a multifocal phase plate lens having multifocal properties distributed throughout the lens. The disclosed lens is comprised of concentric zones, whose diameters are derived from the desired focal length and wavelength of light to focus on. • The effectiveness of the lens is not degraded by overlapping confusing images in the foci. • Cohen patent US 4,340,283 also discloses a plate construction. Multifocal zones suitable for use in optical systems with multifocal requirements. A phase shifted multifocal zone plate provides multiple foci by adjusting the zone plate spacings so that the zone plate foci coincide with the focal points of the multifocal Fresnel lens »adjustment is obtained by ion implantation at certain sections of the zone. thus changing the refractive index of the lens in that section.

In addition, others have attempted to combine refractive and diffractive powers to create multifocal lenses. · US Patent 4,673,707 »Freeman discloses multifocal contact lenses that use diffraction and refraction by adding diffractive power to the basic refractive power of the lens. by a series of concentric zones defined by surface discontinuities or refractive index variations · In the bifocal application, diffractive power is provided in addition to the basic refractive power of the lens while maintaining the basic curvature of the front and rear surfaces. Diffractive zones deflect all incident light in a manner analogous to that of a phase zone plate (Fresnel zone plate) · Freeman Patent US 673 697 teaches that it is important to maintain the radius of curvature of the rear surface of the lens with a value which is in close agreement with that of the meat. Freeman U.S. Patent 4,642,112 discloses bifocal artificial ophthalmic lenses using a transmission hologram to provide diffractive power on a selective basis of wavelengths or amplitudes in a manner that is additive to the refractive power of the lens.

When using a diffraction element to provide two separate focal lengths, the maximum theoretical yield is about 40.5% of incident light forming an image at each focal length. Therefore, the overall overall lens yield is about 81%. The remaining light (about 19 $) is scattered in higher order diffraction patterns, thus degrading the formed images rather than improving them. it would be desirable to provide multifocal lenses that use both diffractive and refractive lenses that have a total overall efficiency closer to 100%,

SUMMARY BA INVENTION

It is therefore an object of the present invention to provide a slow, high performance multifocal. Therefore, the present invention provides higher performance multifocal lenses using at least one diffractive zone situated on a defined portion of the surface of a refractive lens. embodiment of the present invention thus fall into two areas, a first high yield diffractive power area and a second area which does not substantially have diffractive power. More preferably, the diffraction zones provide substantially 100% yield in the + 1 diffractive order. The non-diffractive zones allow light to be transmitted without appreciable deviation due to diffraction. »More preferably, the zones have roughly equal areas so that half of the incident light focuses on each of the two focal planes, resulting in this. an overall lens yield approaching $ 100,

In another preferred embodiment, lenses are provided which have two different diffractive elements arranged substantially across the entire surface of the lens. The two diffractive patterns are different in that they have different diffractive powers. As the diffractive powers are additive to a basic power of the provided by the lens on which the diffractive elements are arranged, a high power multifocal lens with high performance is obtained. »For example, high efficiency zones can be provided», which are highly efficient with diffractive powers of about 10 diopters and 14 diopterias for foot and distance vision, respectively. These diffractive powers are additive to the basic refractive power of the lens on which they are placed, for example a 10 diopter biconvex lens. Thus, in this example, an optical power of 20 diopter for long distance vision and 25 diopter for short distance vision are proposed. Since diffractive zones are preferably high yield diffractive elements, a bifocal lens approaching 100% yield is provided.

DESCRIPTION OF DRAWINGS

The figures of the drawings represent:

Fig. 1, a graph of the optical yield of a diffractive lens element}

Fig. 2 is a plan view of a preferred embodiment of a lens made according to the present invention having two diffractive elements divided into an annular zone and a circular zone.

Fig. 3 is a plan view of another preferred embodiment of a lens made in accordance with the present invention having a single diffractive element consisting of an annular zone.

Fig. 4 is a plan view of a preferred embodiment of the present invention having two diffractive elements each divided into two zones.

Fig. 5 is a plan view of an intraocular lens made in accordance with the present invention having a far vision zone and a near vision zone defined by bisecting the lens.

Fig. 6 is a plan view of an intraocular lens made in accordance with the present invention which has a far vision zone and a near vision zone dividing the lens into quadrants.

Fig. 7 is a schematic representation of the passage of light through a slow intraocular bifocal taken 5;⁼ according to the present invention?

<img file="PT97656A_D0002.tif" />

<img file="PT97656A_D0003.tif" />

<img file="PT97656A_D0004.tif" />

Fig. 8 is a schematic representation of the moon passing through a bifocal contact lens made in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention has numerous advantages over the above described designs. Primarily, the present invention increases the aggregate overall lens yield. Ideally, 50% of the inefficient light is provided for each focal point. An image of distant objects and an image of nearby objects is provided. The present invention provides the maximum possible contrast and image definition. Preferably, the high throughput diffraction zone has an optical yield with maximum practical value, ie about 98%. In a preferred embodiment, a high performance diffraction grating is produced. As about 9θ% of the light passing through the diffractive zones will be focused on the retina to nearby objects and substantially all light passing through the refractive zones will be focused on the retina for distant objects, better multifocal vision is achieved. Therefore, the present invention overcomes the problem of unwanted light scattering caused by higher order diffraction. Thus, the lenses according to the present invention have a higher potential yield than any prior art conception.

As mentioned above, the maximum theoretical yield available from a normal phase zone plate is about 81%. The diffractive / non-diffractive intermittent construction according to the present invention can yield considerably higher yields. The performance of a diffractive lens element is shown graphically in FIG. 1 as a percentage of transmitted light * Yield. It is plotted against the step height, in micrometers, on the lens surface for a silicone water lens. A first curve (50) illustrates the zero-order diffraction yield. A second curve (52) illustrates the s-diffraction yield.

<img file="PT97656A_D0005.tif" />

5736776- f.7 ”'

<img file="PT97656A_D0006.tif" />

X * first order. In the typical prior art lenses described above, a step height equivalent to slightly more than 3 micrometers was chosen to equally divide the first order and zero order diffraction gradients, thus making about 40% of the light be distance-focused, long-distance focal · Overall performance and thus about 80% · But in lenses according to the present invention, a step height of 6 micrometers is chosen. As shown clearly in fig. 1, for this step height value, almost 100% of the incident light is refracted in the first order. Thus, almost 100% of the light can be focused both at short and long distance focal lengths. Providing alternating sectors with 100% yield, joining focused for the short distance and others for the long distance, a slow with about 100% yield is achieved.

In fig. 2 is a plan view of a slow embodiment according to the present invention. The lens may be used in either a contact lens or an intraocular lens, therefore, unrelated features such as contact elements for attaching an intraocular lens to the eye are not shown in the figure.

The bifocal vein is preferably obtained by providing a lens, such as a biconvex diffractive lens, which has basic power and creating high performance diffractive zones (10, 12), which provide additive diffractive power to the basic power of the lens. It will be understood that the term additive power refers to the arithmetic addition of the power of the lens elements, so in certain embodiments, the diffractive power may be negative and reduce the overall power of that zone.

As shown, in a preferred embodiment, it is desirable to place a circular diffractive zone (10) approximately on the central axis of the lens and to arrange a second diffractive zone in a spaced annular relationship with the first. Situated between the diffractive zones (10, 12) are refractive zones (2, 22), which have only the basic power of the lens. Therefore, a part of the incident light will fall into the refractive zones «7«

<img file="PT97656A_D0007.tif" />

vas (20, 22) · provides focus at first focal length · optical yield of this aerial zone equal to optical yield of basic slow a, if manufactured to high Mayan commercial standards, will approach $ 100 . Another portion of the incident light will fall into the diffractive zones (10, 12) and also pass through the basic lens. Thus, the power of this part of the lens will be the additive sum of the diffractive or refractive powers and will provide focus at a second focal length. Higher commercially available techniques for applying a diffractive element are used to create diffractive zones (10, 12), thus providing a yield of about 98%. Therefore, the overall lens effectiveness is close to 100% yield.

In a typical application to an intraoarar lens, the lenses as shown in FIG. 2 have a total diameter of about 7 * 0 mm · More preferably, the inner diffractive zone (io) will have an air diameter of 1.72 mm, the first refractive zone (20) will have an outer diameter of about 2.90 mm, the next diffractive zone will have an outer diameter of about 4.60 mm and the second refractive zone will have an outer diameter of about d * 7 * 00 mm · As one of ordinary skill will understand, project dimensions may vary somewhat to obtain particular corrective effects. You will also understand that the order of placement of diffractive and refractive zones may be reversed, i.e. the central zone may be refractive, etc.

In Fig. 3 another embodiment of a lens having similar properties to that shown in Fig. 2 is illustrated. The drawing of the illustrated lens has a centrally located first refractive zone 30, preferably about 1.3 mm in length. diameter if used with an intraoeular lens d * 7.00 mm. Surrounding the first refractive zone (30) is a diffractive zone (4θ), which preferably has an outer diameter of about 3 * 36 mm. · A second refractive zone (32) surrounds the refractive zone (4θ) and has an outer diameter of about 7,00 mm · As mentioned above, in certain embodiments '8'

<img file="PT97656A_D0008.tif" />

It may be desirable to change the dimensions given or to reverse the arrangement of zones.

Referring now to FIG. 4 shows an embodiment of a high performance lens using both diffractive and surface refractive elements to obtain bifocal vision. The lens illustrated in fig. 4 has two zones of a first diffractive power (110, 112) for distance vision and two zones of a second diffractive power (120, 122) for near view. Although the distance from the zones shown places the zones in a series of rings, it should be understood that many other arrangements may be ineluded with the present invention. Also, as shown with reference to FIGS. 2 and 3, the number of zones may be increased or decreased. In this embodiment of the present invention, two different diffractive power zones will be placed in an additive manner relative to a lens with a basic power to obtain multiple focal points. As one of ordinary skill in the art will readily understand, the arrangement, shape and relative dimensions of the zones depends on the intended specific correction.

In a preferred embodiment of the lens illustrated in fig. 4, a lens preferably provides a basic refractive power of about 10 diopter obtained using a biconvex lens or other known lens designs. An additional 10 diepores of a first diffractive power are added by two diffractive zones (110, 112), thereby providing a total power of 20 diopter for distant viewing. Also provided are near vision zones (120, 122) which They have a second diffractive power of about 14 diopters, resulting in a total power of 2 ° dioptres to see on foot.

Referring now to FIGS. 5 and 6, intraocular lenses (200) made in accordance with the present invention are shown. Lenses 200 have contact locking means 210 for retaining the lenses in place. As shown, each lens has foot-sight zones (N) and far-sight zones (f). According to one aspect of the present *

<img file="PT97656A_D0009.tif" />

In the present invention, the paddle or far view zone may comprise a high performance diffractive element, while the other zone comprises a refractive element of the basic lens. Alternatively, as discussed with reference to FIG.

4, in certain embodiments of the present invention, both the paddle and the far-sighted zones will comprise diffractive elements, each respectively having a different diffractive power.

The lenses illustrated in fig. 5 · 6 also illustrate other variations of the geometry of the different focal length zones created on the basic lens. As shown in FIGS. 2 to 4, it will be desirable in certain cases to create one or more circular or annular diffractive zones. As shown in fig. 5 and it is also possible to divide the lenses diametrically into halves or quadrants, thereby alternating the paddle and far-sight zones. As will be readily appreciated by those skilled in the art, the same zone arrangements illustrated in FIGS. 2 to 6 may be applied to contact lenses and other forms of lenses, thus not limited to intraocular lenses.

The operation of an intraocular lens 200 within the eye (250) is shown in FIG. · Light coming from a nearby object (N) is in focus and over the retina (R) through the near vision zone. Light from a distant object (f) is focused on the retina (r) by the far-sighted area of ​​the lens. Therefore, all light from both near and far objects is focused, respectively, by the near or far vision zones, resulting in a lens with a near 100% yield.

Similarly, fig. 8 illustrates a contact lens (100) made in accordance with the present invention placed on the cornea of ​​an eye (250). Contrary to the example of fig. 7, the patient wearing a corrective contact lens also has a natural lens (260) inside the eye.

As one skilled in the art will understand, the above discussed lenses may have a basic reflective power provided by the shape of the lens. The present invention may be applied to biconvex or flat-convex lenses, as well as meniscus lenses, such as as contact lenses ·

Although certain embodiments of the present invention have been set forth in detail, these examples do not represent any limitation. Numerous other embodiments and variations thereof will occur to those skilled in the art. Therefore, reference should be made to the appended claims in determining the subject matter. purpose of the present invention ·

CLAIMS