APPARATUS AND METHOD OF TREATING CONTACT LENSES

Abstract: Contact lenses (8) are placed in a storage case (1) that contains hypotonic saline solution. The container (1) containing the lens and the solution is placed in a microwave oven and the hydrophillic contact lens (8) and the solution are both subject to direct microwave irradiation. During irradiation water vapour is lost from the solution which thereby goes from being hypotonic to isotonic.

Description: APPARATUS AND METHOD OF TREATING CONTACT LENSES The present invention relates to a method of treating contact lenses and to apparatus for treating contact lenses. According to one aspect of the present invention a method of treating contact lenses comprises immersing at least one lens in an aqueous solution and heating with microwaves characterised in that both the solution and the lens are exposed to microwave irradiation. The solution may be altered from a hypotonic solution to a generally isotonic solution during the exposure to microwave irradiation. According to a further aspect, a method of treating contact lenses comprises immersing at least one lens in an aqueous solution and heating with microwaves characterised in that solution is altered from being a hypotonic solution to a generally isotonic solution during the exposure to microwave irradiation. Both the solution and the lens may be exposed to microwave irradiation. The aqueous solution may be less than 0.85% w/v or less than 0.8% or less than 0.7% w/v or in the region of 0.6% w/v or less or in the region of 0.4% w/v or less or in the region of 0.2% w/v sodium chloride to water. Water vapour may be lost during microwave exposure. - 4 - predetermined amount above ambient pressure fluid within the container can escape from the container. The sealing means may be arranged to seal the container after the pressure within the container drops below a predetermined amount. The sealing means may be arranged to seal the container after the pressure within the container drops below a predetermined amount. The present invention comprises apparatus to be used in a domestic microwave oven that enables the wearers of hydrophillic (soft) contact lenses to establish a daily process that in one step simultaneously cleans, disinfects, or sterilises their lenses and storage cases, as well as prepares their own daily supply of disinfected or sterile saline solution. There are already existing patens and patent applications for disinfecting and sterilising soft lenses by use of microwave irradiation. Some of these propose apparatus to shield, or part shield the lenses from direct irradiation and thus to use the microwave cooker to clean the lenses by simply heating the cleaning solution in which they are immersed (see e.g. Kutner et al. PCT number 20 93/15772 & 93/18798 and Stepanski et al. U.S. Patent number 5,164,166). Others propose exposing the lenses to direct irradiation in such a way as to actually dehydrate them during the sterilisation process (see e.g. Rohrer et a, U.S. Patent number 4,971,773). This can damage the structure of the lens and also make it difficult to rehydrate the lens adequately prior to using the lens again. The method may comprise locating the lens in a container during microwave irradiation which container includes a valve. Vapour from the solution in which the lens is immersed may be allowed to escape once the pressure of the vapour is in the region of, or exceeds two bars. The method may comprise treating two or more lenses simultaneously. A weight may be arranged to prevent escape of vapour below a predetermined pressure. A thermal load may be provided in addition to the aqueous solution in which the lens is immersed. The thermal load may comprise an aqueous thermal load. Alternatively or additionally the thermal load may comprise a radar absorbent material. According to a further aspect of the present invention apparatus for treating contact lenses comprises a first container for aqueous solution and at least one contact lens, the apparatus further including a second container for aqueous solution which second container is in fluid communication with the first container whereby, in use, fluid from said first container may leave the first container on heating and fluid from said second container can subsequently enter the first container. According to yet another aspect of the present invention apparatus for treating contact lenses comprises a container for at least one contact lens, the container being associated with releasable sealing means whereby, when the pressure within the container rises above a - 6 - A process comprising of one operation that simultaneously exposes a) hydrophillic contact lenses, b) a conventional type of contact lens storage case and c) an aqueous cleaning solution such as saline, to direct irradiation inside a microwave cooker. Whereby the said lenses and said storage case are cleaned, disinfected or sterilised and the said solution is disinfected or sterilised and where the said solution is saline the process reduces the said saline to an isotonic solution the wearer may use to place the said lenses onto the eye. A secondary process following from process above, where once the said process of irradiation is completed, the said storage case is aseptically filled by back siphonage of disinfected solution, while the cap of the said case is secured. Whereby, the disinfected contents of the said case are left closed off from further inlet of fluid and subsequently, the said storage case may be completely sealed by screwing or pushing the cap of the said storage case tight on its casing. A first apparatus for the method and processes in which the apparatus exposes hydrophillic contact lenses mounted in the lens holder of a conventional type of lens storage case to direct irradiation inside a microwave cooker, whilst keeping the said lenses immersed in an aqueous cleaning medium. The said apparatus comprises of: - a contact lens storage case comprising of a lens holder assembly with an adjustable cap closure and a lens cup constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 120°C The present invention disinfects or sterilises the lenses by exposing them simultaneously to the combined effects of direct irradiation and of heating in an aqueous cleaning solution. This exposure enables a number of important cleaning and care steps to be combined in just a single process that: removes organic deposits from lenses through the action of intensive heating in a turbulent medium: disinfects or sterilises the lenses; prepares a disinfected or sterile saline solution that the wearer can use to place contact lenses onto the eye: cleans, disinfects or sterilises contact lens storage cases, including existing types of carrying case. Thus the apparatus described under the present invention permits the lens wearer to follow a daily cleaning regime that is more practicable and familiar than earlier microwave methods. Compared to conventional chemical systems, the said regime offers the wearer the opportunity to clean, disinfect or sterilise their lenses and storage cases and prepare their own saline on a daily basis that is much cheaper, quicker, is hypoallergenic and uses less pharmaceutical packaging. A method of treating hydrophillic contact lenses, comprising immersing the said lenses in an aqueous solution and heating with microwaves, characterised in that both the said solution and said lenses are exposed to microwave radiation. - 8 - a contact lens storage case comprising of a lens holder assembly with a turn cap closure and a lens cup constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 120°C. the said storage case being dimensioned so that microwave radiation can penetrate through the saline solution it contains and into the contact lenses immersed in the said solution; a cap closure for the said storage case that can be adjusted, by screwing or pushing, to make either a fluid tight seal on the said lens cup, or to restrict the free movement of fluid in and out of the said lens cup; a lens cup of sufficient size to hold contact lenses completely immersed in aqueous cleaning solution for the time it takes to disinfect or sterilise the said lenses by microwave irradiation; a lens holder assembly that extends sufficiently far into the said lens cup to hold contact lenses completely immersed in aqueous cleaning solution for the time it takes to clean, disinfect or sterilise the said lenses by microwave irradiation; a second container constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 140°C, formed to contain material that absorbs surplus microwave energy. a one way valve that may be fitted to the cap of the said second apparatus, the said valve comprising of a chamber with an inlet isolated from an outlet by a seal a cap closure for the said storage case that can be adjusted by screwing or pushing, to make either a fluid tight seal on the said lens cup, or to restrict the free movement of fluid in and out of the said lens cup: a container constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 120°C. - the said container being formed so that it can hold the said contact lens storage case immersed in an aqueous cleaning solution for the time it takes to clean, disinfect or sterilise contact lenses by microwave irradiation: the said container and storage case being dimensioned so that when the said storage case is placed inside the said container, microwave radiation can penetrate through the aqueous solution contained by both said vessels and directly into the contact lenses within the storage case; a lid for the said container constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 120°C the said lid may be formed both to contain material that absorbs surplus microwave energy, and to have a projection(s) extending from the underside of the said lid, such that when the said apparatus is assembled ready for irradiation, the bottom of said projection is positioned just above the top of the said storage case. A second apparatus for the method and processes recited in Claims l, 2 and 3 comprising of: - 10 - a second container constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 120°C, formed to contain material that absorbs surplus microwave energy. An apparatus for the method the said apparatus comprising of: a top plate having a channel(s) of appropriate depth and width to hold the tops of contact lens storage bottles; a bottom plate having a channel(s) of appropriate depth and width to hold the bottoms of contact lens storage bottles; a locking bolt and nut to joint the two said plates together, whereby the said assembly of plates can clamp a number of the said storage bottles in a single assembly of plates and bottles, ready for placing inside a microwave cooker; the said plates being constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 140°C; the said nut and bolt being constructed of materials suitable to be used within a microwave cooker; - the said top plate being constructed of material that allows for an elastic movement at its rim when the said rim is subjected to a static force greater than 1 bar, whereby the rim of the said plate acts as a spring when subjected to upward forces. that is weight or spring loaded to open at the pressures arising from a required operating temperature of 120-140°C, whereby steam can escape from the said apparatus, via the said valve outlet. An apparatus for the method and process the said apparatus comprising of: a pair of separate storage chambers, each of sufficient size to hold an individual contact lens completely immersed in an aqueous cleaning solution for the time it takes to disinfect or sterilise the said lens by microwave irradiation; - the said chambers being dimensioned so that microwave radiation can penetrate through the saline solution it contains and into the contact lenses immersed in the said solution. - a single lid, or two adjustable cap closures, that either rest upon, or fix to the apertures of the said chambers; the said lid and closures being formed to keep them seated over the said chambers in a fit that permits heated fluid to escape from the said chambers when the said apparatus is exposed to microwave irradiation and closes off the chamber to airborne contaminants after the said irradiation has ceased; the said apparatus being constructed of materials that are transparent to microwave radiation and not deformed by temperatures in the order of 120°C ; - 12 - In typical operation, the contact lenses are removed from the eye and placed into the lens holder assembly 4 in the normal way. The lens cup 3 is filled with 7.5 ml of purified 0.6% w/v saline solution that is hypotonic. Thus the saline is made up with less than the 0.9% w/v sodium chloride added to purified water that is required to make isotonic saline. This allows for a proportion of the saline solution to be lost as vapour during heating, after which the solution will be left in a generally isotonic concentration. Then the loaded lens holder 4 is screwed into the cup 3 so that the seal 5 in the lens holder cup is secured on the rim of the lens cup neck - but not actually screwed down tight onto the rim. Another 30 ml of 0.6% w/v saline solution is poured into a circular cleaning bath 2, having a diameter of less 40 mm at a lower cylindrical end - and the loaded storage case 1 is then put into the filled bath 2. Then 100 ml of tap water may be poured into the load vessel 7, in order to raise the thermal load of the apparatus to the minimum load recommended by the manufacturers of microwave cookers. Alternatively, the additional thermal load may be provided by fixing a block of radar absorbent material into the vessel 7 during manufacture. This load vessel 7 is then placed as a lid on top of the cleaning bath 2. The load vessel 7 has a fin 9 projecting from its underside, that acts to hold the storage case 1 down below the liquid level inside the cleaning bath 2 during heating. The whole apparatus is then placed into a microwave cooker and typically heated at full power for 3 minutes. Alternatively the power may be applied at a medium level REFERENCES CITED AND HEREBY INCLUDED PATENTS: Kutner et al. PCT number WO 93/15772, 1993 & WO 93/18798, 1994 Roher et al, U.S. number 4,971,773, 1990 Stepanski et al, U.S. number 5,164,166, 1992 OTHER PUBLICATIONS: Rohrer M.D. et al, . "Microwave Sterilisation of Hydrophillic Contact Lenses" - American Journal of Ophthalmology, 101(1) : 49-57, 1986 Olsen CM. et al, "Some biological effects of microwave energy",. Journal of Microwave Power 1:45, 1966 The present invention may be carried into practice in various ways, but several embodiments will now be described by way of example and with reference to accompanying drawings in which: Figure 1 shows a schematic drawing of an indicative apparatus. The parts of the apparatus are constructed of appropriate materials like the temperature resistant thermoplastics that can be used in a microwave cooker. The soft lenses 8 are placed in the lens holder assembly 4 of a conventional barrel type of contact lens storage case 1 that comprises of closable baskets for securing the lenses, the said baskets being fixed into a screw cap 6 that screws onto a vessel called the lens cup 3. - 14 - Radiation from a microwave cooker can penetrate aqueous matter inside a microwave transparent container to a depth of 20-40 mm. The diameter of the bath 2 in Figure 1 reduces to 30 mm in the area immediately surrounding the lenses, which permits the lenses and any organisms on them, to be directly penetrated by microwave radiation. During a 2 or 3 minute irradiation, typically about half to one third of the fluid inside the storage case 1 which may originally contain 7.5 ml escapes past the seal and screw threads of the lens holder cap 6. After irradiation, as the temperature and pressure inside the storage case 1 decreases, a siphon effect is created and saline from the bath 2, that may have gone from being hypotonic to isotonic, is drawn back into the case 1, refilling it completely, in an aseptic manner. Hence, at the end of the cleaning and disinfecting cycle, the lenses are left isolated from airborne contaminants inside a closed storage case 1, located inside a covered bath chamber 2 and surrounded by isotonic solution. The closed storage case 1 can then have its disinfected contents completely sealed for transport or long term storage, by lifting it out of the bath 2 and screwing the cap 6 tight on the lens cup 3, which requires about l/8th of a turn. As soon as the saline solution in the case has cooled to room temperature, which solution has gone from being a hypotonic solution to an isotonic solution, the same solution may be used to place the lenses on to the eye. The remaining solution in the bath 2 can be kept as an additional daily supply of disinfected saline for rinsing the lenses, by replacing the load vessel 7 on top of the bath 2 and storing. It will be appreciated that the placing of a lens having a hypotonic solution on the eye can cause liquid from the eye to be drawn off the eye into for 2 minutes. The time and power setting is dependent upon the power rating of the particular microwave cooker. During irradiation, heated vapour can escape from the bath 2 by raising the load vessel 7 off its seating on the rim of the cleaning bath 2. Heated vapour can also escape from the storage case, by passing around the seals and screw threads of the storage case cap 6, which action then cleans and disinfects these parts. Cleaning, disinfecting and sterilising of the lenses and their storage case is effected by the combination of two actions: 1) heat transfer to the lenses from the aqueous medium in which they are immersed - as occurs in a conventional heat disinfection unit for contact lenses: 2) the effect of microwave radiation within living organisms in or on the lens. Radiation within a microwave cooker reverses the polarity of the bipolar molecules in an aqueous medium at frequencies in the order of 2450 MHz. This oscillation causes internal friction within the irradiated medium, which leads to a rapid rise in its temperature. Most living organic cells contain aqueous matter which can be affected in this manner by microwave irradiation. Therefore, even organisms having membranes that resist external heat transfer, can have their cell contents rapidly subjected to the said effects of microwave radiation, providing the membranes are transparent to the radiation. In addition, there is some evidence to suggest that certain cell types may be killed by the so-called non-thermal effects of microwave irradiation, such as cleavage (see e.g. Rohrer et al (1986) and Olsen et al (1966). - 16 - 14 to be screwed down tightly onto the cup 11 immediately after microwaving, sealing the case and making it transportable. A load vessel may also be provided for use with this apparatus. In order to permit a sterilisation equivalent to autoclaving, this apparatus of Figure 2 may have a one way valve fitted into its cap or casing (see Figure 2) . The valve piston 16 is held closed at room temperature by the spring 25. When the temperature inside the case has risen to the order of 120°C, with an internal pressure of around 2 bars, steam can escape the case into the valve chamber 23, via the outlet 29, raising the valve piston 26 and exiting via the valve outlet 24. The required pressure is predetermined by the retaining force of the spring or weight. The operating pressure of this system may then be controlled during irradiation by one or more of the following combination of factors: i) adjusting the power setting of the microwave cooker, ii) adding additional thermal load to the load vessel, iii) calculating the additional thermal load created when more than one unit is irradiated simultaneously. Figure 3 shows yet another apparatus that facilitates the care regime described under the present invention. This storage case does not use baskets to hold the lenses in a vertical position during treatment. As shown in Figure 3, this embodiment is not a carrying case, but could be made into one, if the chambers were mounted by screw caps or other types of locking closure. A load vessel may also be provided for use with this apparatus. The apparatus comprises of two chambers 31 and 32, into which the left and right lenses can be individually placed along with saline solution. A common lid 33 rests the lens. If the lens is in a hypertonic solution then the eye can sting and the lens is reluctant to stay on the curvature of the eye as the as the osmotic pressures are different and the eye will generate excess water. The same apparatus also allows for another modified regime of cleaning and disinfection. In this alternative regime, instead of placing the loaded lens holder 4 into the lens cup 3, the lens holder is placed directly into a larger amount (typically 30 - 40 mm) of 0.6% saline solution inside the cleaning bath 2 and the empty lens cup 3 is placed loosely on top of the lens holder 4. The whole assembly is then irradiated as described above, after which the lens holder 4 and cup 3 can be removed from the bath 2 - the lens 8 can be inserted - and treated solution from the bath 2 poured into the storage case 1 as an additional daily supply. Figure 2 shows a second indicative apparatus for effecting the same care regime. In this apparatus, the lens cup 11 accommodates at least twice as much solution as the 12 ml lens cup of a conventional carrying case, in order to keep the lenses fully immersed during a three minute irradiation, which typically loses at 10 ml of saline solution from the cup. The apparatus in Figure 2 comprises of a contact lens carrying case, with a lens holder assembly 12 similar to that in Figure 1, except that the stem 13 of the lens holder assembly is elongated to carry it down into its larger cup 11. In the operation of apparatus 2 , the cap of the case 14 is tightened in the same manner as for apparatus 1. This creates a loose fit between the lens holder assembly 12 and cup 11 that permits vapour to escape around the screw threads during microwaving, and then allows the cap - 18 - Plates 44 and 45 are locked around the bottles 41 by screwing a wing nut 47 onto the bolt 46. The whole assembly is then loaded into the microwave cooker and irradiated for a time typically around 4 minutes, the exact power and time being determined by the type of cooker used and the required outcome of disinfection or sterilisation. As in the case of apparatus 2 above, the operating temperature and treatment time may be calculated by adjusting either or both the total thermal load and the power setting of the microwave cooker. The thermoplastic material of the plate 44 is naturally elastic over linear distances corresponding to the 120 - 150 mm radius of the plate 44. Thus as the temperature and pressure rises inside the bottles 41 during irradiation, their caps 42 are pushed upwardly, which pushes up the rim of the plate 44, that is only fixed at its centre. When the cups 42 are pushed 1-2 mm out of their bottles 41, hot vapour can escape and further movement of the caps 2 is resisted by the plate 4 above, which arrangement keeps the caps 2 still seated some 2 mm within the bottle necks 1 throughout irradiation. Trials have shown that a lid weighing 2 kg can keep silicone rubber caps seated 2 mm inside 30 glass storage bottles during irradiation, whilst still permitting the free escape of hot vapour from the said bottles. Thus an operating temperature of just over 100°C can be maintained by a relatively weak spring, and full disinfection achieved within 60 - 90 seconds after the temperature of the solution has reached 100°C. To raise the temperature in the bottles above 100°C, the greater spring force required to act against the bottle caps can be achieved by a plate 44 having an on top of the chambers. The lid is held in place over the containers by flanges 34 which are broken at intervals so that during heating, vapour can escape by partially raising the lid high enough off its seat to allow the vapour out, but not high enough to dislodge the lid flanges from the rim surrounding the chamber openings. Thus the lid can close off the chamber to airborne contaminants once the heating process is complete. When the saline in the chambers has cooled to room temperature, the wearer may pick out the lenses and insert them directly into the eye. Figures 4A and 4B schematically show an apparatus for microwave disinfection or sterilisation of soft lenses in batches, as required in commercial use. Here, the lenses 43 are kept in conventional 10 ml storage bottles 41, usually made of glass and having push fit caps 42 made of a heat stable material such as silicone rubber. In typical operation, some 30 bottles 41 each containing a lens immersed in 10 ml of 0.2% saline are loaded onto a circular plate 45 of typical radius 120 - 150 mm having a 30 mm channel set in it to locate the bottles during treatment. This plate 45 may be constructed of a suitable high temperature thermoplastic such as polycarbonate. The plate 45 has a bolt 46 rising through its centre. The bolts 45 and its nuts 47, 410 and 411 may be made of a suitable high temperature thermoplastic. A second similar plate 44 is then placed on top of the bottles 41, such that the bottle caps 42 are also located in a channel and the stem of the bolt 46 goes through a hole in the centre of the plate 44. The centre of plate 44 is supported by a spacing nut 40 that can be screw adjusted to the required position along bolt 46 and then locked in that position by the locking nut 411. - 20 - Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed. appropriate thickness for its radius. The temperature and pressure inside the bottles 41 is then determined by the extent to which the spring force at the rim of the plate 44 permits the caps 42 to rise out of their bottles 41 and thus fix the temperature inside the said bottles, as a function of the rate at which vapour may escape the said bottles. The principal compromise made in this kind of partially vented system is loss of solution from the bottles, which is typically 7 ml over 10 minutes for a batch of 30 bottles. Following irradiation, the temperature inside the bottles 1 cools and a vacuum develops, which draws the partially dislodged caps 2 back into their bottles and creates a firm seal that can be protected as normal, with a crimp type metal closure when the bottles have cooled. All of the embodiments may be arranged to lose water vapour to turn a solution from a hypotonic solution to an isotonic solution as described in relation to Figure 1. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. - 22 - 7. A method as claimed in any preceding claim in which the solution is at above atmospheric pressure during at least part of the exposure to microwave irradiation. 8. A method as claimed in any preceding claim in which vapour escapes around a part which is normally sealed during exposure to microwave irradiation. 9. A method as claimed in any preceding claim in which the lens is heated by heat transfer from the aqueous solution. 10. A method as claimed in any preceding claim in which the lens is heated by microwave irradiation directly heating the lens. 11. A method as claimed in any preceding claim in which living organisms on or in the lens are directly heated by microwave irradiation. 12. A method as claimed in any preceding claim in which the distance from the lens through the solution is, at the least point of distance, less than 50 mm or less than 40 mm or less than 30 mm or in the region of 15 mm. 13. A method as claimed in any preceding claim comprising a container having aqueous solution and at least one lens being in that solution with a further aqueous solution being provided whereby, after the solution in the container is heated and vapour has escaped therefrom during microwave irradiation, liquid from said further solution is drawn into the container on cooling. 14. A method as claimed in Claim 13 in which the further solution is hypotonic prior to the microwave irradiation

Claims: CLAIMS 1. A method of treating contact lenses (8) comprising immersing at least one lens (8) in an aqueous solution and heating with microwaves characterised in that both the solution and the lens are exposed to microwave irradiation. 2. A method as claimed in Claim 1 in which the solution is altered from a hypotonic solution to a generally isotonic solution during the exposure to microwave irradiation. 3. A method of treating contact lenses (8) comprising immersing at least one lens in an aqueous solution and heating with microwaves characterised in that solution is altered from being a hypotonic solution to a generally isotonic solution during the exposure to microwave irradiation. 4. A method as claimed in Claim 3 in which both the solution and the lens are exposed to microwave irradiation. 5. A method as claimed in any preceding claim in which the aqueous solution is less than 0.8% sodium chloride to water or less than 0.7% sodium chloride to water or in the region of 0.6% or less sodium chloride to water or in the region of 0.4% or less sodium chloride to water or in the region of 2% sodium chloride to water. 6. A method as claimed in any preceding claim in which water vapour is lost during microwave exposure. but becomes substantially isotonic during microwave irradiation. 15. A method as claimed in any preceding claim comprising immersing the lens in at least 15 ml of saline solution or at least 20 or in the region of 24 ml of saline solution prior to microwave irradiation. 16. A method as claimed in any preceding claim comprising locating the lens in a container during microwave irradiation which container includes a valve. 17. A method as claimed in any preceding claim in which vapour from the solution in which the lens is immersed is allowed to escape once the pressure of the vapour is in the region of, or exceeds two bars. 18. A method as claimed in any preceding claim comprising treating two or more lenses simultaneously. 19. A method as claimed in any preceding claim including a weight arranged to prevent escape of vapour below a predetermined pressure. 20. A method as claimed in any preceding claim including a thermal load in addition to the aqueous solution in which the lens is immersed. 21. A method as claimed in Claim 20 in which the thermal load comprises an aqueous thermal load. 22. A method as claimed in Claim 20 or 21 in which the thermal load comprises a radar absorbent material.

Inventors: THOMPSON PAMELA, THOMPSON, PAMELA
Applicants: THOMPSON PAMELA, THOMPSON, PAMELA
Application year: 1996
Main classification: A61L2
IPC codes: A61L12