WO2001075510A1

WO2001075510A1 - Variable focus optical apparatus

Info

Publication number: WO2001075510A1
Application number: PCT/GB2001/001449
Authority: WO
Inventors: Joshua David Silver
Original assignee: Joshua David Silver
Priority date: 2000-03-30
Filing date: 2001-03-30
Publication date: 2001-10-11
Also published as: AU2001244344A1; GB0007810D0

Abstract

A variable focus optical apparatus (10), particularly suitable for the correction of presbyopia, comprises at least one variable focus lens (12) having a cavity formed by two sheets (20, 22), at least one of which is flexible. The apparatus is supplied with the lens connected to a pump for introducing fluid into the cavity. The lens as supplied has little or no optical power, and the amount of fluid in the pump is preferably sufficient, and more preferably only sufficient, to increase the power to around 5 dioptres. In a preferred form, the sheets of the lens are positioned on either side of a first ring (24), and a second ring (26) is clamped over the first ring and the sheets to retain them in place. The invention also extends to the lens itself.

Description

VARIABLE FOCUS OPTICAL APPARATUS

The present invention relates to a variable focus optical apparatus, and more particularly to an optical apparatus suitable for the correction of presbyopia.

Presbyopia is a problem with vision which is normally associated with aging. The elasticity of the crystalline lens of the eye tends to reduce with increasing age, and this reduction in elasticity reduces the range of accommodation of the lens. As a result, it becomes harder for a presbyopic person (presbyope) to focus on objects near to the eye, and the near point of distinct vision is moved further from the eye, thus impairing the presbyope's near vision.

The onset of presbyopia usually occurs in the mid 40s in North America and Europe. However, it has been reported that the onset is earlier for people living near the equator, and can occur in the early 30s.

Presbyopia is normally treated using spectacles with positive lenses. The use of such spectacles allows a presbyope to focus at nearer distances than can be achieved with uncorrected vision, which can be essential for close work, reading and so on.

There are several different ways in which a presbyope can obtain spectacles to correct their near vision in this way. One way is to visit an optician, who will be able to measure the person's eyesight accurately and prescribe lenses which will correct the vision in each eye. However, this approach can be rather expensive, particularly if the presbyope's vision deteriorates further and a further pair of spectacles are required. A cheaper option is to buy a pair of mass-produced spectacles. A number of companies produce spectacles of this nature, with simple positive lenses in a range of powers. The differently powered spectacles can be sold from displays in pharmacies or the like, and a presbyope can try various powers until he or she finds the most appropriate spectacles.

While obtaining correction in this way is relatively simple and cheap, the correction is unlikely to be perfect, as the lens power is selected from a relatively limited range of possibilities. For example, if the correction required is 1.6 dioptres (1.6 D) , but the spectacles only come with I D, 1.5 D or 2 D lenses, then perfect correction is not possible. It is also the case that correction may not be selected for the actual working distance for which the spectacles will be used.

In addition, it is common for both lenses in spectacles of this type to be of the same power. However, the degree of presbyopia is not necessarily the same in both eyes of a presbyope, and so a pair of spectacles which corrects the vision in one eye may not correct vision in both.

It would be desirable to provide a cheap device for correcting presbyopic vision, which can accurately correct the vision in both eyes, even if the degree of correction required by each eye is different .

According to a first aspect of the present invention, there is provided a variable focus optical apparatus for the correction of presbyopia, comprising at least one variable focus lens, said lens having a cavity containing a variable amount of transparent fluid defined between first and second transparent sheets, at least one of said sheets being flexible, the cavity being connected to a pump to allow fluid to be introduced into and removed from the cavity, wherein said lens as originally supplied has little or no optical power, and wherein the pump can be used to pump fluid into the cavity to increase the optical power of the lens.

The use of variable focus lenses allows proper correction of eyesight, as the focus of the lens can simply be varied until the appropriate power is reached at the actual working distance. Since the lens as supplied has little or no optical power, it is merely necessary for the user to use the pump to pump fluid into the lens until the appropriate power is attained. Further, if, as preferred, the optical apparatus includes two variable focus lenses, proper correction can be achieved, even if the correction required differs for each eye .

Preferably, the pump contains sufficient fluid for the power of the lens to be increased to a level suitable for the correction of presbyopia. In a particularly preferred form, the pump contains sufficient fluid for the power of the lens to be increased to around 5 dioptres . It has been found that most cases of presbyopia can be treated with lenses having powers between 1 and 5 dioptres. It is therefore desirable for the apparatus as supplied to have enough fluid in the pump to enable most cases of presbyopia to be treated. It is further preferred that the pump contains only enough fluid for the power of the lens to be increased to around 5 dioptres. This reduces the overall weight of the apparatus, and in addition reduces the amount of fluid required in the manufacturing process, while still allowing most cases of presbyopia to be treated. In a preferred construction, the sheets are positioned on either side of a first ring and held in place by a second ring, which comprises a main part extending circumferentially around said first ring and first and second flanges extending radially inwardly from said main part, and each sheet is retained between a flange and a side of the first ring. It should be appreciated that the rings need not be circular, and can have any desired shape. It is preferred that the first and second rings are arranged to retain the flexible sheet under tension. It has been found that this improves the optical characteristics of the flexible sheet. In a preferred form, one of the sheets is rigid. It is further preferred for this rigid sheet to have substantially no optical power. Preferably, the front sheet of the lens is rigid and the rear sheet of the lens is flexible.

According to a second aspect of the invention, there is provided a variable focus lens for use in optical apparatus, comprising a cavity containing a variable amount of transparent fluid defined between first and second transparent sheets, at least one of said sheets being flexible, the cavity being connectable to a pump to allow fluid to be introduced into and removed from the cavity, wherein the sheets are positioned on either side of a first ring and held in place by a second ring, said second ring comprising a main part extending circumferentially around said first ring and first and second flanges extending radially inwardly from said main part, each sheet being retained between a flange and a side of the first ring. A preferred embodiment of the invention will now be described by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a front view of the apparatus ,- Figure 2 is a schematic cross-sectional view of a lens of the apparatus; and

Figure 3 is an enlarged view of a part of Figure 2. As can be seen from Figure 1, the apparatus takes the form of a pair of spectacles 10. However, rather than the lenses 12, 14 of the spectacles 10 being formed from glass or plastic, and thus having a fixed power after their manufacture, the lenses 12, 14 of the spectacles are formed as variable focus lenses.

Variable focus lenses are known per se, and can take the form of a volume of fluid enclosed by flexible transparent sheets. Normally, there are two such sheets, one forming the front surface of the lens and one forming the back surface. The sheets are attached to one another at their edges, either directly or to a carrier between the sheets, to form a sealed chamber containing the fluid. Fluid can be introduced into or removed from the chamber to vary its volume. As the volume of liquid changes, so the curvature of the sheets, and thus the power of the lens, also varies. It is also possible to construct such lenses with one flexible sheet and one rigid sheet .

As best seen in Figure 2, which shows a cross- section of one of the lenses of a preferred embodiment of the optical apparatus, the lens 12 is formed with a rigid front sheet 20 and a flexible rear sheet 22.

The front sheet 20 is formed from polycarbonate, or a similar plastic. In the preferred embodiment, it is formed as a curved plate, but does not have appreciable optical power.

The flexible rear sheet 22 is preferably formed from Mylar, although other transparent flexible materials can be used.

The sheets 20, 22 are attached to the front and rear sides, respectively, of a central ring 24. It is the shape of this ring which determines the overall shape of the lens 12. The lens can be circular, oval, or of any desired shape, and an example of a lens shape obtainable in this way is shown in Figure 1. Preferably, the ring 24 is made from titanium, but any material with similar qualities of strength and lightness, including certain plastics materials, could be used.

The sheets 20, 22 are retained on the ring 24 by means of a second ring 26, which (as best shown in

Figure 3) has a generally "U" -shaped cross-section. The limbs of the "U" , which are in the form of inwardly- directed flanges 28, 30, are arranged to overlie the edges of the rigid and flexible sheets 20, 22, and clamp them against the central ring 24. It is this clamping that holds the lens together. The clamping also maintains a fluid seal between the sheets and the rings. The second ring 26 can again be formed of titanium, aluminium or a similar material .

In order to achieve good optical quality, the flexible sheet 22 should be held under tension at all times. This can be done by configuring the surfaces of the central ring 24 and the second ring 26 between which the edge of the flexible sheet 22 is held in such a way as to hold the membrane under tension.

One way of doing this, as shown in Figure 3, is to form the rings such that one of the surfaces 32 has a recess 34 in it, into which a projection 38 on the other surface 36 engages. Before the projection 38 enters the recess 34, it contacts the flexible sheet 22, and frictionally engages with it. Then, as the projection 38 enters into the recess 34, it stretches the sheet 22, putting it under tension. When the projection is fully received in the recess, the sheet is held under tension.

The space 40 between the sheets 20, 22 is filled with a transparent fluid, such as silicone oil. As mentioned above, the power of the lens is varied by varying the volume of the fluid in the lens 12, and so it is necessary to be able to introduce fluid into and remove fluid from the space 40 in order to adjust it. To this end, a passage 42 is formed through the central ring 24 and the second ring 26, as shown in Figures 2 and 3. This passage 42 allows fluid to pass into or out of the space 40, to adjust the volume of fluid therein.

As the passage 42 is the only way for fluid to enter or leave the space 40, it is desirable for the cross-sectional area of the passage 42 to be as great as possible, to increase the flow rate of fluid in the passage, and thus increase the speed at which the lens 12 can be adjusted. It will be appreciated that it is also desirable for the thickness of the lenses to be as small as possible, both for aesthetic purposes and to reduce the overall weight of the optical apparatus. Thus in the preferred embodiment, the passage 42 is formed as a slot which extends for a short distance around the edge of the lens 12. This allows the passage to have a relatively large cross-section without increasing the thickness of the lens .

In an alternative form, the central ring 24 can be formed with a region which is "honeycombed" with a large number of holes. This increases the total area of the central ring which is available for fluid flow, while maintaining a sufficient level of strength in the central ring. The central ring is subjected to a crushing force when the second ring is clamped over it, and obviously has to resist this force in order to avoid damage to the lens .

A polycarbonate cover 44 is attached to the rear surface of the second ring 26. The purpose of the cover 44 is to protect the flexible sheet 22. It will be appreciated that if the flexible sheet 22 is punctured, the lens will not be usable, as the fluid inside the space 40 will leak out. Protection of the flexible sheet 22 is therefore very important. It will be appreciated that, in reality, there are no gaps between the various parts of the lens through which fluid could leak. In the drawings, gaps are shown between the various parts to show the construction of the lens more clearly. The optical apparatus is supplied with the spaces of the lenses filled with fluid. Each space is connected via a duct to a pump, which can be used to pump fluid into or out of the space to vary the focus of the lens. The pumps may be rotary pumps of the type described in WO 99/47948.

The optical apparatus can be adjusted by a user to correct his or her own near vision, as follows. The user puts on the apparatus in the same way as a normal pair of spectacles, and then attempts to focus on a nearby object (for example, a book, a computer screen or the like) . Due to the user's presbyopia, he or she will probably be unable to obtain a sharp focus of the object on the retina. The user then closes or covers one eye, and uses the pump to pump fluid into or out of the space of the lens in front of the open or uncovered eye. As mentioned previously, this adjusts the power of the lens . The user continues pumping until the lens reaches the appropriate power to correct the user's near vision in the open or uncovered eye, obtaining sharp focus of the object on the retina. The user then changes eyes, and adjusts the other lens until it is also at the appropriate power for the other eye .

The ducts joining the spaces 40 (more accurately, the passages 42) to the pumps can be sealed at this stage, and the pumps removed. This renders the optical apparatus 10 less bulky, and also reduces its weight, which can be important considerations if a user is carrying out close work. However, closing the ducts and removing the pumps means that the optical apparatus can no longer be adjusted.

Alternatively, the ducts and pumps can remain attached to the apparatus, allowing further adjustment to the apparatus. This may be preferred in practice, as the lens power needed to correct the user's near vision for reading may differ from that needed to correct their vision for using a computer, and so on. If the pumps are left attached, then the power of the optical apparatus can be adjusted to allow for this.

The apparatus has the advantage that the lens power can be set at the actual working distance in which the apparatus is to be used. There is no need for a user to guess at the power required, as may be necessary if, for example, spectacles are bought from a display in a pharmacy or the like as mentioned above.

As mentioned above, the spectacles are initially supplied with the chambers filled with fluid, and are preferably at zero power as supplied. To adjust the lenses to the correct power, it is then necessary for a user to pump fluid into the chambers of the lenses, to increase their power. The apparatus can be supplied with enough fluid in the pumps to give a maximum power for the lenses of around 5 D, which will accommodate most presbyopes . However, the spectacles can be capable of a higher maximum power if desired. Further, although the front sheet was described above as having no appreciable power, it can act as a positive lens, if desired. This can be useful as it can reduce the overall mass of the apparatus following the removal of the pumps, by reducing the amount of fluid present in the chambers of the lenses. Normally, in order to increase the power of the lens, more fluid must be pumped into it. As a result, when the variable focus lens has a power of 2 dioptres, it contains more fluid (and so has a greater mass) than when it has a power of 1 dioptre. If the front sheet has no optical power, then all of the power must be supplied by the variable focus lens, with a consequent increase in mass. However, if the front sheet acts as a lens of, say, 1 dioptre, then the variable focus lens need only have a power of 1 dioptre to provide an overall power of 2 dioptres, and so less fluid is required to achieve this correction.

In addition, the front sheet 28 and/or the rear cover 44 can have some cylindrical lens power. Non- circular lenses can introduce astigmatic errors, which are obviously undesirable. However, the provision of some cylindrical lens power can compensate for these errors .

It will be appreciated that the optical apparatus described above allows for simple and accurate correction of presbyopia.

Claims

1. A variable focus optical apparatus for the correction of presbyopia, comprising at least one variable focus lens, said lens having a cavity containing a variable amount of transparent fluid defined between first and second transparent sheets, at least one of said sheets being flexible, the cavity being connected to a pump to allow fluid to be introduced into and removed from the cavity, wherein said lens as originally supplied has little or no optical power, and wherein the pump can be used to pump fluid into the cavity to increase the optical power of the lens.

2. Apparatus as claimed in claim 1, wherein said pump contains sufficient fluid for the power of the lens to be increased to a level suitable for the correction of presbyopia.

3. Apparatus as claimed in claim 1 or claim 2, wherein said pump contains sufficient fluid for the power of the lens to be increased to around 5 dioptres.

4. Apparatus as claimed in claim 3 , wherein said pump contains only enough fluid for the power of the lens to be increased to around 5 dioptres .

5. Apparatus as claimed in any preceding claim, wherein the apparatus comprises two variable focus lenses, one for each of a user's eyes.

6. Apparatus as claimed in any preceding claim, wherein the sheets are positioned on either side of a first ring and held in place by a second ring, said second ring comprising a main part extending circumferentially around said first ring and first and second flanges extending radially inwardly from said main part, each sheet being retained between a flange and a side of the first ring.

7. Apparatus as claimed in claim 6, wherein said first and second rings are arranged to retain said flexible sheet under tension.

8. Apparatus as claimed in claim 6 or claim 7, wherein one of said sheets is rigid.

9. Apparatus as claimed in claim 8, wherein said rigid sheet has substantially no optical power.

10. Apparatus as claimed in any preceding claim, wherein the front sheet of the lens is rigid and the rear sheet of the lens is flexible.

11. A variable focus lens for use in optical apparatus, comprising a cavity containing a variable amount of transparent fluid defined between first and second transparent sheets, at least one of said sheets being flexible, the cavity being connectable to a pump to allow fluid to be introduced into and removed from the cavity, wherein the sheets are positioned on either side of a first ring and held in place by a second ring, said second ring comprising a main part extending circumferentially around said first ring and first and second flanges extending radially inwardly from said main part, each sheet being retained between a flange and a side of the first ring.

12. A lens as claimed in claim 11, wherein said first and second rings are arranged to retain said flexible sheet under tension.

13. A lens as claimed in claim 11 or claim 12, wherein one of said sheets is rigid.

14. A lens as claimed in claim 13, wherein said rigid sheet has substantially no optical power.

15. A lens as claimed in any preceding claim, wherein the front sheet of the lens is rigid and the rear sheet of the lens is flexible.

16. Optical apparatus substantially as described herein with reference to Figures 1 to 3.

17. A lens substantially as described herein with reference to Figures 1 to 3.