WO2011107723A1

WO2011107723A1 - Multifocal lens

Info

Publication number: WO2011107723A1
Application number: PCT/GB2010/000404
Authority: WO
Inventors: John Trevor De Carle
Original assignee: John Trevor De Carle
Priority date: 2010-03-05
Filing date: 2010-03-05
Publication date: 2011-09-09

Abstract

A multifocal, in particular bifocal contact lens has a plurality of annular concentric refractive zones which alternate between a first zone having a first refractive length such as reading vision and a second zone having a second refractive length such as distance vision. At least one of the first zones has a greater annular area than both a second zone radially inward of it and a second zone radially outward of it. The contact lens may be provided such that when fitted to an eye at least 50% of light enters the pupil through the reading zones for each size of pupil between the maximum and a minimum so that a greater amount of light comes through the parts correcting for near vision.

Description

Multifocal Lens

This invention relates to multifocal lenses, such as bifocal contact or intraocular lenses.

Bifocal contact lenses which have a plurality of annular zones designed to correct for both near and distance vision have been known for some time and have proved reasonably popular. Examples of such lenses are described for example in British Patent No. 2295686 and lenses made according to the design described therein have seen the market share for bifocal contact lenses rise. However, despite improvements it is understood that relatively few patients who try bifocal contact lenses keep using them.

An improvement was made to the bifocals according to GB2295686, by providing a much greater number of zones and EP1212652 describes such a lens.

A feature common to both the lenses mentioned above is the aim for a ratio of 50:50 in terms of light reaching the retina from the reading zones and the distance zones so that one does not overpower the other.

Pupil size varies between people and varies according to light (generally speaking a maximum diameter of 8-9mm is not unusual for young people, with size shrinking with age such that once presbyopia sets in around age 45, the diameter may be as small as 2-3mm). The average pupil diameter for people who are likely to wear bifocal lenses is around 4mm. In order to achieve close to the intended 50:50 ratio (and come within the acceptable range of 40:60 to 60:40 set out in both patents mentioned above) despite the fact that pupil diameter varies, it is typical for each annular zone to have approximately the same width (the distance measured between the inside radius and outside radius).

Accordingly, moving away from the optical axis of the contact lens the area of each adjacent reading/distance zone increases owing to the relationship of the area of a circle (or segment thereof) to the square of its radius. Obviously the larger the number of zones, the closer the lens will come to the ideal 50:50 at all pupil diameters. In view of the relatively low percentage of people who are happy with the result from current bifocal contact lenses, the invention seeks to provide an alternative that provides improved performance for at least some patients.

Accordingly, the invention provides a multifocal contact lens having a plurality of annular concentric refractive zones which alternate between a first zone having a first refractive length corresponding to one of distance vision or reading vision and a second zone having a second refractive length corresponding to the other of distance vision or reading vision; characterised in that at least one of said first zones has a greater annular area than both a second zone radially inward of it and a second zone radially outward of it.

The invention may also include at least one second zone that has a greater annular area than both a first zone radially inward of it and a first zone radially outward of it.

There may be a plurality of first zones that have greater annular areas than both second zones inward of them and second zones outward of them.

There may also be a plurality of second zones that have a greater area than both first zones inward of them and first zones outward of them.

The lens may include a radially inner region where a plurality of first zones each have a greater area than both the adjacent inward second zone and the adjacent outward second zone. In this case it is preferable that the first zone is a reading zone The lens may also include a radially outer area where a plurality of second zones each have a greater area than both the adjacent inward first zone and the adjacent outward first zone. In this way, the greater area of the first, preferably reading, zones in the inner region can be compensated by the greater area of the second, preferably distance zones in the outer region.

Alternatively the contact lens may be provided such that when fitted to an eye at least 50% of light enters the pupil through the first zones for each size of pupil between the maximum and a minimum. In this case, it is preferable that the first zones are reading zones, so that a greater amount of light comes through the parts correcting for near vision.

Conventional thinking is that 50:50 for every size of pupil is the ideal, otherwise one image will appear pale and superimposed on the other. However, it seems that at least for some patients greater than 50% presents an improvement, with indications that the best overall vision could be where the ratio of light entering through the reading zones to light entering through the distance zones is about 63:37. Other suitable ranges are specified in claims 11-13.

The invention will be illustrated by the following, non-limiting, description and the accompanying drawings in which:

Figure 1 shows a plan view of a first kind of lens;

Figure 2 shows a plan view of the inner region of the central viewing area of a lens;

Figure 3 shows a cross section of part of the inner region of the central viewing area of the lens shown in figure 2;

Figure 4 shows a cross section of part of the intermediate region of the central viewing area of the lens;

Figure 5 shows a cross section of part of the outer region of the central viewing area of the lens;

Figure 6 shows a cross section of a lens according to a second embodiment of the invention; and

Figure 7 shows a cross section of a lens according to a third embodiment of the invention.

Referring to figure 1 it will be seen that the lens 1 has a central viewing area 2 which should be large enough to cover an entire pupil at its maximum opening. This depends of course on the eye concerned, but is suitably between 4.5 to 8mm in diameter. The central viewing area 2 is divided into three regions, an inner region 2A, an intermediate region 2B and an outer region 2C. In this embodiment the three regions have approximately the same radial width (i.e. distance from their inner diameter to their outer diameter). The inner region 2A, intermediate region 2B and outer region 2C are all provided with a series of closely spaced alternating distance zones 4 and reading zones 5 (not visible in figure 1 ).

Figure 2 shows a plan view of the inner region 2A in which a central circular distance vision zone 3 is shown shaded and is surrounded by annular concentric refractive zones. The annular concentric reading zones alternate between first, reading, zones 5 having a first refractive length corresponding to reading vision and second, distance, zones 4 having a second refractive length corresponding to distance vision. (In order to distinguish easily between the distance and reading zones, distance zones 4 are shown shaded and reading zones 5 are shown unshaded. The skilled reader will of course appreciate that to be effective, both types of zones must allow light to pass through them and will therefore usually be transparent.) It will be seen that there are seven reading zones 5 and six distance zones 4, but as has been previously discussed a large total number of zones is preferable and there could be up to 50 zones in the inner region, or even more.

It will be seen that at least one of said first reading zones has a greater annular area than both a second zone radially inward of it and a second zone radially outward of it. In fact, in this embodiment all the reading zones have a radial width of at least double that of the adjacent distance zones and therefore they all satisfy the criteria of having a greater area than the adjacent inward zone and than the adjacent outward zone.

The reader may gain a greater understanding of the invention from figure 3 which shows a cross section of the inner region 2A along a radius. This view has been greatly exaggerated to show the different reading zones 5 and distance zones 4 and it will be clear from this view that in the inner region the total area of the reading zones through which light will enter the pupil is greater than the area of the distance zones through which light will enter the eye.

It will be understood that although not shown in figure 3, the width of the reading zones 5 to the distance zones 4 may vary across the radius of the inner region, in this case it is preferable for the width to decrease from the centre.

Figure 4 shows the intermediate region 2B of the lens 1 in which the width of the reading zones 5 and the distance zones 4 are approximately equal. Again only seven reading zones 5 and seven distance zones 4 are shown, but it is preferred to have as many zones as possible - current lathes are quite capable of manufacturing bifocals with as many as 80 zones, and it is considered that as many as 150 zones may be optimal, so it may be preferred to have more zones in the intermediate region. Because of the approximately equal widths of the zones in the intermediate region 2B, this region is most similar to prior art bifocal contact lenses and in this region, the annular area of each zone increases outwardly step by step.

Figure 5 shows the outer region 2C of the lens, which in this first embodiment have second, distance, zones 4 which are wider than their adjacent first, reading, zones 5 and therefore have a larger annular area than both first zones immediately adjacently inward of them and first zones immediately adjacently outward of them. This feature of the sum of the second zones 4 in the outer region having an overall area that is larger than the sum of the area of the first zones 5 means that although in the inner region 2A there may be substantially more than 50% of the light entering through the reading zones 5, this is compensated for by the fact that in the outer region 2C a greater amount of light enters through the distance zones 4.

It will of course be appreciated that for a given radial width, the outer region 2C covers a much greater area than the inner zone 2A, and that because of this the relative difference in the annular areas of the reading zones 5 and distance zones 4 in the outer region 2C can be less than those in the inner region 2A, or that the outer region 2C can have a smaller radial width than that of the inner region 2A.

A second embodiment of the invention is shown in figure 6 in which the central viewing area 2 is not split into regions and the first zones 5 and second zones 4 extend across it. In this case, the annular area of the first, reading, zones 5 is consistently greater than the annular area of the adjacent inward distance zone and greater than the area of the adjacent outward distance zone. In this way, when fitted to an eye at least 50% of light enters the pupil through the first zones 5 for each size of pupil between the maximum and a minimum, so that a greater amount of light comes through the parts correcting for near vision .

In this embodiment it can be seen that there is a gradual reduction in the width of the first and second zones away from the central circular distance vision zone 3.

In tests, good results have been achieved by a contact lens made according to this specification, but with a total of 80 zones of decreasing width. The lens had the following dimensions when dry: a central circular distance vision zone 3 of radius

0.207mm; followed by a reading zone 0.266mm wide; then a distance zone 0.166 mm wide; and decreasing to a final pair of zones with the near measuring 0.035mm and subsequent distance zone 4 measuring 0.024mm over a total diameter of the central viewing area of 4.274mm. As will be well understood, once the lens is wet and ready for wearing, there is a certain amount of swelling, bringing the total wet diameter of the central viewing area 2 to 5.50mm. The total wet diameter of the lens 1 was 14.2mm.

A third embodiment is shown in figure 7 where the relative width of the first, reading, zones 5 to the second, distance, zones 4 begins in favour of the reading zones with the ratio of the areas of the reading zones to the adjacent distance zones at least 60:40, but with the ratio between the relative areas of the first, reading, zones 5 to the second, distance, zones 4 in the inner region 2A gradually coming closer to 50:50 away from the central circular distance zone. It may be considered in this embodiment that the design has an inner zone 2A which merges straight into the outer zone 2C without the intermediate zone and once the outer zone is reached, the ratio begins to favour the distance zones 4. Again, only 28 zones are shown because of the difficulties of distinguishing between so many zones on a page. However, a greater total number of zones would be favoured.

As for the method of manufacture of the lenses described above, it can be seen in figures 1 and 2 that the lens is generally circular, and from figures 3-7 that the lens has an anterior power surface and a posterior base curve with the distance and reading vision zones formed in the posterior base curve. It can also be seen that in these examples half of the reading addition effect is achieved by the portions which are flatter than the cornea (i.e. the reading zones) and half is provided by the curve that is steeper than the cornea (i.e. the distance zones). It would of course be possible for the distance curvature to match the corneal curve and produce the entire reading effect from the reading zones.

Lenses in accordance with the invention may be made from hard materials

(preferably gas-permeable), or from high water content soft lenses of a central thickness typical of minus lenses such as 0.06mm. Specifically, material of the hydrated hydrophilic polymer type are suitable, so that the lenses are formed by machining or moulding a xerogel and the resulting products are then swollen by hydration to produce the final lenses. When the lenses are made as proposed above, with the reading and distance zones formed on the posterior base curve, the gap between the junction of the zones and the cornea, where the lens is the greatest distance away from the cornea should be minimised to avoid the inner surface of the lens being pressed onto the cornea deteriorating the effect of its reading addition. Preferably, this distance should be less than about 0.007mm, preferably between 0.003 and 0.006 or less.

It will be appreciated that by forming the reading correction on the rear surface of the lens, the same profile of the rear surface can be used with a variety of front surface curvatures, depending on the basic distance correction required. Thus if lenses in accordance with the invention are manufactured by casting a monomer composition, the same rear surface mould half can be used with a number of different front surface mould halves to reduce the inventory required.

Lenses in accordance with the invention may be manufactured by machining, or by moulding (casting). In the case of casting, the master moulds will be produced by machining the desired profile into the master mould half from which the casing moulds are produced.

The zones may be formed on the posterior lens surface by continuously changing the radius of the cutting tool. As will be appreciated, the alternate distance and reading refractive zones may be formed directly using a high precision computer controlled lathe, or cut into the surface of the mould from which the lenses are produced.

Although in the embodiments described above, the central circular zone 3 is designed for distance vision and the adjoining annular zone 5 for reading, it will be appreciated that the situation may be reversed. It will also be appreciated that the embodiments described above are mere examples and having read this disclosure, the skilled man should be able to envision various alternative variations of the zones that fall within the scope of the invention as defined by the claims.

Although the embodiments described above refers to bi-focal lenses, other multifocal lenses such as trifocals with vision zones divided into alternate near, intermediate and distance zones may be manufactured according to the invention. It would also be possible for the lenses to have the reading and distance zones blending into one another where they meet.

It is also possible that some or all of the zones may be formed by diffractive rings rather than the refractive annular zones described; see US4637697 for more information.

The power surface is not discussed in detail above, but as in prior art lenses, the shape of the power surface can introduce a progressive variation of power across the viewing area of the lens. Alternatively the progressive variation can be introduced by introducing the aspherical surface on the posterior surface by progressively varying the power of the distance zones towards the periphery. The progressive power changes suggested in US6685315 may be suitable, i.e. negative changes from the centre to the periphery not exceeding about 1 Dioptre, preferably not more than about 0.75-0.8 dioptres and generally within the range of 0.25-0.75 dioptres. Specifically, a power change of -0.5 dioptres from the centre to the periphery may be useful.

Claims

Claims:

1. A multifocal lens having a plurality of annular concentric refractive zones which alternate between a first zone having a first focal length corresponding to one of distance vision or reading vision and a second zone having a second focal length corresponding to the other of distance vision or reading vision; characterised in that at least one of said first zones has a greater annular area than both a second zone radially inward of it and a second zone radially outward of it.

2. A multifocal lens according to claim 1 further comprising at least one second zone having a greater annular area than both a first zone radially inward of it and a first zone radially outward of it.

3. A multifocal lens according to claim 1 or 2 comprising a plurality of first zones having greater annular areas than both second zones inward of them and second zones outward of them.

4. A multifocal lens according to claim 3 further comprising a plurality of second zones that have a greater area than both first zones inward of them and first zones outward of them.

5. A lens according to any of the preceding claims having a radially inner region where a plurality of first zones each have a greater area than both the adjacent inward second zone and the adjacent outward second zone.

6. A lens according to any of the preceding claims wherein the first zones are reading zones.

7. A lens according to any of the preceding claims comprising a radially outer area where a plurality of second zones each have a greater area than both the adjacent inward first zone and the adjacent outward first zone.

8. A lens according to any of the preceding claims wherein the second zones are distance zones.

9. A multifocal lens according to claim 1 comprising an inner region wherein the overall area of the first zones is greater than the overall area of the second zones wherein the ratio of the area of the first zones to the area of the second zones gradually decreases towards the periphery so as to provide an outer region where the overall area of the second zones is greater than the overall area of the first zones.

10. A multifocal lens according to claim 1 wherein the ratio of the annular area of the first zones to the annular area of the second zones are such that when fitted to an eye at least 50% of light enters the pupil through the first zones for each size of pupil between the maximum and a minimum.

11. A multifocal lens according to claim 10 wherein the ratio of the annular area of the first zones to the annular area of the second zones are such that when fitted to an eye at least 60% of light enters the pupil through the first zones for each size of pupil between the maximum and a minimum.

12. A multifocal lens according to claim 11 wherein the ratio of the annular area of the first zones to the annular area of the second zones are such that when fitted to an eye between 60% and 65% of light enters the pupil through the first zones for each size of pupil between the maximum and a minimum.

13. A multifocal lens according to claim 10 wherein the ratio of the annular area of the first zones to the annular area of the second zones are such that when fitted to an eye approximately 63% of light enters the pupil through the first zones for each size of pupil between the maximum and a minimum.

14. A multifocal lens according to any one of claims 10 to 13 wherein the first zones are reading zones, so that a greater amount of light comes through the parts correcting for near vision.

15. A multifocal lens according to any of the preceding claims comprising third zones of intermediate focal length interposed between at least some of the alternating first and second zones.

16. A multifocal lens according to any of the preceding claims in the form of a contact lens or an intraocular lens.

17. A multifocal lens substantially as described herein, with reference to the accompanying drawings.