AP908A

AP908A - An optical apparatus and method.

Info

Publication number: AP908A
Application number: APAP/P/1997/001152A
Authority: AP
Inventors: David Joshua Silver
Original assignee: David Joshua Silver
Priority date: 1995-06-01
Filing date: 1996-06-01
Publication date: 2000-12-04
Also published as: PL182796B1; NO975457D0; AU6229996A; HUP9901447A3; AU707789B2; MX9709320A; EE03979B1; DE69631477T2; TR199701476T1; EP0830620B1; GB9511091D0; SK159397A3; EP0830620A1; CN1191608A; CN1133883C; WO1996038744A1; OA10638A; JPH11505941A; CA2223031A1; KR19990022167A

Abstract

In the field of eyesight correction, there-is a need for "universal" spectacles that can be tailored in situ to suit individual's requirements. The disclosure relates to an apparatus, which may be in the form of a pair of spectacles (10) including one or more liquid lenses (lla, l1b). , The apparatus also includes a sealable duct (24) and a pump (e.g a syringe) for -adjusting the pressure of liquid in the liquid lens. In use, the apparatus is adjusted to provide eyesight correction for an individual. The duct (24) is then sealed, thereby rendering the apparatus subsequently non-adjustable and therefore permanently tailored to the requirements of the individual. The disclosure also relates to an apparatus in the form of a flexible membrane mirror.

Description

This invention relates to an optical apparatus and method. In particular, the invention relates to an optical apparatus comprising at least one liquid lens or flexible membrane mirror, and more particularly to a pair of spectacles constituted by or including such an apparatus.

The invention also relates in particular to a method of adjusting an optical l

apparatus for correcting defective eyesight, io

It is known to provide a liquid, lens . in the form of;one or more 'transparerif, circular, flexible membranes clamped about a peripheral zone to define a cavity. The cavity is filled with a transparent liquid, the pressure of which is adjustable by means of a positive displacement pump

... -15· ··· such as.ύ· syringe.·;·· ·· ; - ‘ T ' ·/ ‘^; ·' *

Adjustments of the pressure of fluid in the cavity cause variations in the curvature of‘the iehs defined by the membranes and fluid, thereby giving rise to a lens of infinitely variable optical power. .

' ' ·'··

US Patent No. 4,890,903 gives further details of liquid lenses, and of optical instruments such as spectacles incorporating such lenses. The entire disclosure of US Patent No. 4,890,903 is incorporated herein by reference.

The history of liquid lenses goes back several decades, yet there has not previously been a proposal for a truly practical sight-correcting device incorporating such lenses.

AP/P/ 9 7/01152

According to a first aspect of the invention, there is provided an optical ife. 5Λ908 . apparatus- comprising: ,-.

at least one liquid lens or flexible membrane mirror; a liquid pump for adjusting the pressure of liquid in the or a cavity of the lens or mirror;

a closeable duct for interconnecting the said cavity and the pump permitting the flow of liquid therebetween; and a closure for closing the duct when the pressure of liquid in the said cavity attains a desired value, whereby to render the lens or mirror subsequently non-adjustable.

The.principal advantage of such an arrangement over previous apparatuses is that the liquid lens or lenses become non-adjustable after adjustment of the lens or lenses to a desired setting. This is in contrast to previous apparatuses, in which the liquid lenses have remained perpetually ·'. 15 '· ·' adjustable? ••'Thus·,- previous liquid lens' apparatuses' could riot'be· incorporated into spectacles partly because of the cumbersome nature of the pumps needed for adjustment of the lenses; and partly because of the • risk of the optical power of the· lenses deviatirig from optima tailored for the' wearer of the spectacles.

'

Thus, an apparatus according to the invention confers a robustness and practicality not achievable with previous liquid lens designs.

AP/P/ 9 7 / 0 11 5 2

Preferably the closure includes a portion of the duct plastically deformable 25 to close the duct. In particularly preferred embodiments, the duct is plastically deformable when compressed and or when heated.- A further possibility is for the duct to be plastically deformable when subjected to ultrasonic excitation.

The foregoing features mean that apparatus according to the invention_can

C t 0 3 _ ...·/. · readily .be adjusted to'a preferred optic's! power* of the lenses.' and easily ' set at the preferred optical power.

Conveniently, the pump is a positive displacement pump capable of 5 increasing and decreasing the pressure of liquid in the cavity. In particularly preferred embodiments, the pump is a syringe.

Syringes are mass-produced at extremely low cost, and therefore they provide a simple, inexpensive means of setting the power of the lenses of an apparatus according to the invention, eg. in a harsh environment.

In some embodiments of the invention, the closure preferably includes a member retentively deformable to close the duct. One form of such a member is a resiliently deformable bung closing the duct. For use with

*.:· 15 .· such 'a' bung, -thepump may-include or be Operatively connected to a further duct capable of removably piercing the bung to permit the flow of liquid between the pump and the cavity, the resilience of the bung (a) creating a liquid-tight seat about the further duct when the bung is pierced thereby; and (b) causing closure of the aperture pierced by the further duct on removal thereof from the bung.

In particularly preferred embodiments, the further duct is a hollow needle.

Thus it is possible to devise embodiments of the invention in which the 25 pump is a conventional syringe having a conventional hypodermic needle secured thereto, in order to piece a resiliently deformable’bung that re-sealably closes the duct of the apparatus.

Yet a further possibility for closing the duct is for the retentively 30 deformable member to include opposed, interior walls of the duct capable

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“..’a*/.'·.·; »* *·’'-’'* **'-' V.·'·. *' “*· ; ' ·’ '·.' ’ ·. · '' ¹ ··' .....: _;0f;seaIirigly.;adhering, one to'.another on' compression Of the duct. 'Γη .

preferred embodiments, this is achieved by virtue of adhesive matter secured on the opposed, inner walls of the duct.

Using this embodiment, it is possible advantageously to seal the duct without employing any additional components, other than a simple apparatus such as a pair of pliers or pincers to compress the duct.

I

The invention is also considered to reside in a pair of spectacles including an apparatus as defined hereinabove, the apparatus preferably including a pair of liquid lenses. .._; .....

The advantageous features defined hereinabove in relation to the apparatus are of particular benefit when the apparatus is incorporated in a pair of .·.··· .15··. · spectacles.Tn particular,.spectacle's a&cordirigtc) the'inveritibh provide the’' possibility of correction of many eyesight defects, without the need for a skilled optometrist in assessing the optical power of the lenses required for siich'correction/ This in turn makes the spectacles particularly suitable for use in so-called developing countries, where the incidence of various eyesight defects is high yet there are few skilled opticians and very little equipment for testing of eyesight in conventional ways.

Furthermore, since spectacles according to the invention can be manufactured in large numbers without the need for variation between different pairs of spectacles at the manufacturing stage, the purchase price of spectacles according to the invention can if desired be made sufficiently low to enable their purchase by inhabitants of developing countries or by charities providing aid in such countries.

AP/P/ 97 / 0 1152

Conveniently the pair of spectacles includes a respective liquid pump and

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a.respectire-.ctosable -duct for-each.-lens/ -These·, features 'advantageously·· permit employment of an inventive method of adjusting the spectacles for correcting eyesight defects, as defined hereinbelow.

Preferably the or each closable duct is flexible and the frame of the spectacles includes one or more recesses for receiving the or a duct after closing thereof. More preferably, the or each recess is closable to conceal the closed ducts. This permits the construction of an aesthetically pleasing pair of spectacles, in which the closable ducts are protected from damage.

io

In practical embodiments of the spectacles according to. the invention, each lbns includes a'rigid/transparent cover for protecting a flexible membrane of the lens. Optionally, the or each transparent cover has an optically corrective effect. Multiple protective covers may be supplied if desired, . · .··· 15.·· -Qg.·· on? the -front-and- rear.'face or each·'liquid -lens of the Spectacles·, in ' ' order to protect the lenses against damage.

• ·' If one or more of the protective covers has an opticallycorrective effect, a number of. advantages may inure to spectacles according to the invention. For example, the protective covers may provide a degree of inherent correction in the spectacles regardless of the pressures in the liquid lenses, thereby conveniently limiting the range of adjustment of the liquid lenses required to provide improvements in eyesight for the majority of users of the spectacles.

Also, although it is possible to construct liquid lenses that have a concavoconvex shape, it is far simpler to construct liquid lenses of convex lens shape. Such lenses do not provide correction for conditions such as astigmatism. The protective covers may, particularly if present at the front and rear faces of the liquid lenses, be shaped to provide correction

AP/P/ 97 / 0 1152

- , β? Ο 0 90 5 -/,. - -,,-...-,-¾ · ’·' for such conditions, thereby obviatingthe need for the'liquid lenses'to'· ' provide correction for conditions other than myopia and presbyopia.

Optionally the or each transparent cover has an optical filtering effect.

Thus it is possible in accordance with the invention to manufacture eg. corrective sun glasses and welding masks.

, Preferably the optical apparatus also includes one or more compound, fluid lenses. Further details of such lenses are provided in the io aforementioned US Patent No. 4,890,903.

Embodiments of apparatuses, including spectacles, in accordance with the invention may optionally be such that the or a fluid lens thereof contains a predetermined quantity of liquid, the pump thereof being capable of

15· /'-adjusting thefluid pressure irr the lens -cavity” in a limited'range. Thus it would be possible to manufacture and supply spectacles having a predetermined quantity of fluid, in each lens, and simply connect the . pump, including a small reservoir of the fluid, to each lens at the point of use, ie. when it is required to adjust and set the spectacles for use by an ...

individual. This avoids the need for the pump to include a sufficiently large supply of liquid to fill the lens from empty, although such lens and pump combinations are considered to be within the scope of the invention.

According to a second aspect of the invention, there is provided a method of adjusting an apparatus for correcting defective eyesight, comprising the steps of:

(i) placing an apparatus as defined hereinabove in front of a patient’s eye such that the eye receives light through the or a lens thereof;

(ii) operating the pump of the apparatus until the patient sees an

AP/P/ 9 7 / 0 1 1 5 2 optimum clarity image;

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(iv) detaching the pump from the apparatus.

Desirably, the patient views a distant object during step (ii).

This method is particularly suitable when the apparatus is configured as eg. a monocle or similar device intended for use by one eye only of a patient. Thus this aspect of the inventive method is particularly suitable for patients who have sight in only one eye, a condition common in many io developing countries.

According^;to a'third aspect of the invention, there is provided a method of adjusting an apparatus for correcting defective eyesight, comprising the steps of, in any practical order:

.15 . .... (i). .;.· placing, a pair, of-spectacles-as defined hereinabove in front·'· of a patient’s eyes so that each of the patient’s eyes receives light via a respective lens of the spectacles;

. ^: , (ii) ' obscurihg'the pupil of a first of the patient’s eyes;

(iii) operating the pump of the lens associated with the second of ' the patient’s eyes until the said second eye sees ah optimum clarity image;

AP/P/ 97/01152 (iv) closing the duct between the said lens and its associated pump;

(v) uncovering the pupil of the first eye;

(vi) obscuring the pupil of the patient's second eye;

(vii) repeating steps (iii) and (iv), tmaatis mutandis, with respect to the .patient’s second eye; and .

(viii) detaching the or each pump from the apparatus.

. ;· Desirably step (iii) is carried out each time while the'patient views an · 30 object, which may be either distant or proximal.

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·.··., This'aspect of the inventive.hie'thod-is suitable for patients fiavinglhe•’use'· \ of both eyes, one or both of which require correction.

Conveniently, when the spectacles include a recess as defined hereinabove, the method may include the further steps of:

(ix) after closing, placing each duct in a recess of the spectacles; and (x) covering the or each recess.

io Thus it will be seen that the apparatuses and methods of the invention provide a.convenient, cheap and rapid· means, of correcting eyesight., through use of monocles and spectacles. However, the ability to set the power of the liquid lens deriving from the invention is not limited to applications in which correction of defective sight is required. Further . .-.-is. . exemplary-applications include adjustment of convex mirror's provided for. security in shops and for safety purposes at difficult road junctions; focusing of light beams eg. for use in illuminating buildings, either ’·/· through use of fluid lenses or flexible membrane mirrors; and numerous other occasions when it is required to.tailor the optical power of a lens or mirror to a particular requirement and set the optical power so that it is subsequently non-adjustable.

There now follows a description of preferred embodiments of the invention, by way of example, with reference being made to the accompanying drawings in which:

Figure 1 is a partly sectioned view of a pair of spectacles manufactured in accordance with the invention;

Figure 2a is a cross section on line 2-2 of Figure 1 showing details 30 of the securing arrangement for the membranes of the lenses;

AP/P/ 9 7 / O H 1 5 2

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Figure -2b showsa portion of the Figure '2a arrangement in more detail

Figure 3 shows one form of re-sealable closure for the duct of the spectacles of Figure 1 ;

Figure 4 shows another form of closure; and

Figure 5 shows a pair of spectacles incorporating the Figure 4 embodiment.

Referring to the drawings, there is shown a pair 10 of spectacles in accordance with the invention. As is best shown in Figure 1, the . spectacles .10. include a pair 1.1a, 1 lb of liquid, lenses each of which .may .^Jgenerally be of the kind disclosed in US Patent No. 4,890,903. The lenses 11a, lib are secured in a frame 12 shaped in the conventional manner of spectacles, and including a bridge 12a and a pair of side arms ·15 . 12b.(one^- of Avhich'is visible in’Figure 1) sectired to the frame 12 in a conventional manner eg. through use of rivets or screws 13.

• As is best shown in Figures 2a and 2b, the frame 12 is in the vicinity of each;lens Ila, lib a laminar structure.having a top plate' 14, a bottom· plate 16 and a middle plate 17 sandwiched between the top and bottom plates. A pair of flexible, transparent membranes 18, 19 (eg. of 23 micron thickness type D “Mylar” (RTM) material) are secured respectively between the middle plate 17 and the upper plate 14; and between the middle plate 17 and the lower plate 16, to define a liquid lens cavity 20.

The membranes 18, 19 are circular, and the plates 14, 16, 17 include a circular series of aligned apertures 22 for receiving eg. set screws 23 for clamping the'membranes 18, 19 between the plates.

AP/P/ 97/0115 2 • '.... AF^5, f Ο 9 Ο 8 ; Each*, .aperture' 22 irt·.. the; bottom·· pi ate-1.6- may be^: suitably-tapped for ' engagement with the threaded end of a set screw 23.

As is best shown in Figure 2b, the membranes 18, 19 are clamped by 5 virtue of opposed O-rings 24 in the manner described in US Patent No.

4,890,903. This arrangement ensures that each membrane experiences a radially outwardly directed tension.

The components of Figures 2a and 2b are shown spaced apart, but in use io of the apparatus would of course be clamped tightly together by virtue of the screws 23.

As is shown in Figure 1, the cavity 20 of each lens 11a, 1 lb is connected to a filling duct 24 passing through a portion of intermediate plate 17.

... -.15 . ..Filling·.duct 24 opens-into a· recess 25 that is .open-ended On the exterior of the frame 12 of the spectacles 10. Recess 25 is capable of sealingly receiving eg. a filler tube for the transparent liquid intended to fill the ' lens. Thus, filling of each lens is possible via its associated recess 25 and filler duct 24. .

The Figure 1 embodiment shows a valving member 27 comprising a shaft 27a having a through-going aperture 27b that is alignable with the longitudinal axis of duct 24 in order to permit flow of fluid along duct 24. Shaft 27a is rotatable by virtue of knurled ring 28 in order to rotate aperture 27b out of alignment of the longitudinal axis of duct 24, thereby closing the duct when desired.

AP/P/ 97/01 1 52

The spectacles of Figure 1 include a further, threaded recess 29 extending between a peripheral edge of the middle plate 17 and a further duct 30 also connected to the cavity 20 of each lens 11a, lib. A threaded plug 31

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7'.'is sealirigly ihsertab'iS-.ihtO’recesS -29,. in order ^selectively to seal duct-30

The presence of duct 30 and recess 29 permits the expulsion of gas from cavity 20 during filling thereof. After filling, plug 31 is used to close duct 30 against leakage of liquid.

Although the spectacles of Figure 1 are highly effective in correcting defective vision-, they are likely, by virtue of the valving member 27, plug 31 and generally heavy design of the frame 12, to be regarded as unacceptably cumbersome by potential wearers. The embodiments of

Figures 3 to 5 therefore serve to make the spectacles lighter and more aesthetically appealing.

It is envisaged that production embodiments of the spectacles would be supplied with the lens cavities 20 pre_rfilled with a predetermined volume . ,..15 ; of transparent-liquid;. Since-the'pre-filling-would -be'carried in'a'factory environment, the duct 30 could, after filling, be sealed permanently, eg. by welding, insertion of a settable material or by screwing a flush-fitting plug into a' threaded' aperture' similar to recess 29.- Therefore, mass produced versions of the spectacles would dispense with the plug 31 per se thereby lightening the spectacles and· making them more pleasing aesthetically.

AP/P/ 9 7 Λ0 1152

In the Figure 3 embodiment, the valving member 27 and the recess 25 are dispensed with. Instead, each duct 24 includes a portion 24a that is of enlarged diameter in order snugly to receive a resiliently deformable bung ·· 33 that normally seals duct 24 in a liquid-type manner.

When it is required to adjust the pressure in cavity 20, a hypodermic-type needle 34, operatively secured to a syringe 35 serving as a positive displacement pump for the transparent liquid (eg an inert silicone oil) is λ·'··

-X: J AW'q'q.':?’ 'inserted.· .into duct'24- 'so-'as-'CpmpleteTy· to pierce' bung .33·, 'thereby providing, a fluid communication path between syringe 35 and cavity 20. During this process, the resilience of the material of bung 33 causes bung 33 to seal about needle 34 in a liquid-tight manner, thereby preventing leakage of liquid from the cavity 20.

After adjustment of the pressure in cavity 20, by virtue of movement of the piston of syringe 35, needle 34 is withdrawn from bung 33. The resilience of bung 33 causes the aperture previously formed by needle 34 io to self-seal, thereby closing duct 24 in order to prevent further adjustment of the optical power of the lens 20.

If desired, a suitable cap may be inserted into the upper end 24b of duct 24, in order to prevent in the ingress of dirt, etc.

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An alternative arrangement is shown in Figure 4. In this embodiment, duct 24 opens into an enlarged-diameter portion 36 that itself opens into • an elongate recess 37 formed as'a depression’in the outer surface of the middle portion 17 of frame 12.

'

Enlarged-diameter portion 26 contains seated therein in a conventional manner an O-ring grommet 38 that serves to retain a flexible, hollow tube 39. Grommet 38 seals around tube 39 and around the interior of enlarged diameter portion 36 in a liquid-tight manner, so that tube 39 is capable of communicating liquid, via duct 24, and from cavity 20. Alternatively, tube 39 may be bonded directly e.g.-to duct 24, thereby obviating the need for grommet 38.

AP/P/ 9 71 0 1 1 5 2 . . The-free end 40 of tube'39 maybe connected to-a positive displacement 30 pump such as syringe 35 for adjustment of the pressure of liquid in the

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cavity 20.·'.After adjustment of the liquid pres sure'in· order to'achieve'a” ' desired dioptre setting of the lens 20, the tube 39 is sealed by virtue of a pair of jaws 42 being moved towards one another to seal tube 39.

Tube 39 may be such as to deform plastically under the influence of heat, pressure and/or ultrasonic excitation. Jaws 42 may be such as to supply such forms of energy to tube 39 when jaws 42 are brought into contact , with opposed sides of tube 39.

One particularly preferred form of the jaws 42 that may be of benefit in , .developing countries is a pair of.jaws 42.heated by virtue of a propane ··· burner that would cause plastic, sealing deformation of tube 39 when the jaws 42 are brought together about tube 39.

15··. · Numerous other methods of-sealing tube 39 are possible/ for example a ' constricting collar may be applied to tube 39. Also, alternative methods of securing tube 39 in enlarged-diameter portion 36 may be employed.

After sealing of tube 39, it is tucked into recess 37. A cover 43 may be snap-fitted to the exterior surface of frame 12 as shown in Figure 5, in order to provide an aesthetically pleasing appearance to the spectacles 10.

AP/P/ 9 77 0 1 1 52

The Figure 5 embodiment also shows schematically, in dotted lines, a pair of rigid, transparent covers 44, 45 secured respectively on either side of each lens 11a, lib in order to prevent damage to the lenses. If desired, as previously discussed', the covers 44, 45 may have optically-corrective and/or filtering properties.

In practice, the covers 44, 45 may be contained within the “envelope” 30 defined by the profile of the frame 12, in order to provide an aesthetically f-i.· ?··OT is· /72 ft .a#

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pleasing .appearance to the spectacles-. 'Alternatively;· the-cbvefs'44;-45‘·^:······ύ. · ·’'. · may be retained by virtue of slots or clips on the exterior of frame 12.

There now follows a description of a method of adjusting apparatus for 5 correcting sight defects, in accordance with the invention.

As previously mentioned, the spectacles are likely to be supplied pre-filled with a suitable transparent fluid. The wearer puts the spectacles on, closes one eye and adjusts the pressure of liquid in the lens in front of the other eye whilst looking at e.g. a distant or proximal object object so as to achieve sharp focus for .that eye. The. wearer then.closes the eye. previotisly open, and opensithe eye previously closed. He then adjusts the pressure of liquid in the lens in front of the now open eye, whilst looking at distant object to achieve sharp focus for that eye.

At suitable points in the procedure (after each lens has been set to a desired pressure) the ducts 24 for the respective lenses are closed by one ’· of'the methods disclosed herein, thereby rendering the lenses of the spectacles subsequently non-adjustable. ..

If the embodiment of Figures 4 and 5 is used, after closing of the duct 24 the cover 43 is applied to the recess 37 for each tube 39.

AP/P/ 97 / 0 1 152

A simplified procedure may be adopted when it is required only to correct the vision of one eye of a user of apparatus in accordance with the invention. The simplified procedure involves' looking through an apparatus according to the invention and having at least one liquid lens, whilst looking at a distant object. The pressure of liquid in the lens is then adjusted in order to achieve sharp focus' for the eye the eyesight of which is being corrected. Subsequently, the duct 24 of the apparatus is

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.'•’closed;in g’ccb^dahce’with. one)bftheafOteraenUoned..methods' to' renderthe lens subsequently non-adjustable.

It will thus been seen that the apparatus conveniently provides a iow-cost 5 solution to the problem of correcting eye defects in a great number of people.

Claims

Claims

1. A pair of spectacles comprising: a pair of liquid lenses;

5 a pair of liquid pumps for adjusting the pressure of liquid in a cavity in each said lens;

a pair of closeable ducts for interconnecting each said cavity and the pump permitting the flow of liquid therebetween; and

10 a closure associated with each duct for closing each duct when the pressure of liquid in the said cavity attains a desired value, whereby to render the lens subsequently non-adjustable;

wherein each closeable duct is flexible and the

15 frame of the spectacles includes one or more recesses for receiving the duct after closing thereof.
2 . A pair of spectacles according to claim 1 wherein each closure includes a portion of the duct plastically 20 deformable to close the duct.
3. A pair of spectacles according to claim 2 wherein the said portion of the duct is plastically deformable when compressed.
4. A pair of spectacles according to claim 2 wherein the said portion of the duct is plastically deformable when heated.

30
5. A pair of spectacles according to claim 2 wherein the said portion of the duct is plastically deformable when subjected to ultrasonic excitation.
6. A pair of spectacles according to any preceding

35 claim wherein each pump is a positive displacement pump capable of increasing and decreasing the pressure of liquid in the said cavity.

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- 17
7. A pair of spectacles according to claim 6 wherein the pump is a syringe.
8. A pair of spectacles according to any preceding 5 claim, wherein each closure includes a member retentively deformable to close the duct.
9. A pair of spectacles according to claim 8 wherein:

(i) the said member includes a resiliently
10 deformable bung closing the duct; and (ii) the pump includes or is operatively connected to a further duct capable of removably piercing the bung to permit the flow of liquid between the pump and the said cavity, the resilience of the bung (a) creating a

15 liquid-tight seal about the further duct when the further duct pierces the bung, and (b) causing closure of the aperture pierced by the further duct on removal thereof from the bung.

20 10. A pair of spectacles according to claim 9 wherein the further duct is a hollow needle.
11. A pair of spectacles according to claim 8 wherein the retentively deformable member includes opposed,

25 interior walls of the duct capable of sealingly adhering one to another on compression of the duct.
12. A pair of spectacles according to claim 11 including adhesive matter secured on the opposed, inner

30 walls of the duct.

AP/P/97/Ol 152
13. A pair of spectacles according claim wherein the or each recess is the closed ducts.

to any preceding closeable to conceal
14. A pair of spectacles according to any preceding claim wherein each lens includes a rigid, transparent

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18 cover for protecting a flexible membrane of the lens.
15. A pair of spectacles according to claim 14 wherein the or each transparent cover has an optically corrective effect.
16. A pair of spectacles according to claim 14 or claim 15, wherein the or each transparent cover has an optical filtering effect.
17. A pair of spectacles according to any preceding claim, wherein the optical apparatus includes one or more compound, fluid lenses.
18. A pair spectacles according to any preceding claim, wherein the or a fluid lens thereof contains a predetermined quantity of liquid, the pump therefor being capable of adjusting the fluid pressure in the lens cavity in a limited range.

1S2
19. A method of adjusting a pair of spectacles correcting defective eyesight, comprising the steps of, in any practical order:

(i) placing a pair of spectacles according to any preceding claim in front of a patient's eye so that each of the patient's eyes receives light via a respective lens of the spectacles;

(ii) obscuring the pupil of a first of the patient's eyes;

(iii) operating the pump of the lens associated with the second of the patient's eyes until the said second eye sees an optimum clarity image;

(iv) closing the duct between the said lens and its associated pump;

(v) uncovering the pupil of the first eye;

(vi) obscuring the pupil of the patient's second eye;

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- 19 (vii) repeating steps (iii) and (iv), mutatis mutandis, with respect to the patient's second eye; and (viii) detaching the or each pump from the apparatus .
20. A method according to claim 19 comprising the further steps of :

(ix) after closing, placing each duct in a recess of the spectacles; and (x) covering the or each recess.