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Ultrasound cleaning and disinfection of contactlenses: A preliminary report
Ultrasound Cleaning and Disinfection of Contact Lenses: A Preliminary Report Anthony J. Phillips, P. Badenoch & C. Copley cleaners used in conventional cleaners and disinfectant solutions. . Simplicity of use providing combined cleaning and disinfection procedures with no risk of misabuse. U l t r a s o u n d - - M o d e of A c t i o n Ultrasound is the range of sound waves of higher frequency than those to which the human ear is sensitive. The auditory range is approximately from 100 cycles per second (100Hz) to 15,000 or 16,000 cycles per second (15 to 16 kHz). Above 16-20 kHz the sound waves result in no sense of hearing in the human ear and are referred to as ultrasound. Fig 1
Ultrasonic Cleaning (modified after Roetzheim @ )
ULTRASOUND INTENSITY
Metal Welding ] & cutting Destructive ",~ Metal Etching !
~ , P a i n t Stripping
~
Introduction
Practitioner and patient disenchantment with current contact lens cleaning products due to reasons of cost, complexity, adverse reactions, availability, inadequate performance, etc., have led to examination of alternative systems. The search for a simple, fool-proof system that provides both a cleaning and disinfection action has led to the recent introduction of portable, patient ultrasonic units. As little is known about such units, and because recent reports and claims have been made in the lay press and on television, this preliminary report has been written to aid practitioners in their understanding of the system and to provide initial research data. The advantage claimed for patient ultrasonic units are:-1. Increased lens life because of reduced deposit formation. 2. Increased comfort due to a maintained clean surface. 3. Effective anti-microbiological action 4. No toxic or allergic reaction to the preservatives or Anthony J. Phillips, P. Badenoch & C. Copley, The Flinders Contact Lens Research Group of South Australia.
20
Acceleration of Non chemical destructive ~ reactions
Ideal level for contact < lens cleaning and disinfection
Fault detection
Ultrasonic devices may be divided into destructive or non-destructive devices, (Roetcheim, W. 1979) the former designed to alter the media in which the waves are formed and the latter not altering the media. Figure 1 shows that ultrasonic contact lens cleaners exist at the border of destructive and non-destructive devices, that is, the unit must be powerful enough to remove contaminants and produce lens disinfection, but gentle enough to avoid harming the lens material. The cleaning action of ultrasonic units is produced by a process known as cavitation. The ultrasound waves produced by the transducers in the unit produce frictional forces within the liquid medium. This produces both heat and the liberation of microscopic bubbles. These bubbles re-dissolve almost immediately producing an implosion or 'cavitation' effect. Because most cavitation occurs at, or very close to, solid surfaces,
Transactions of B.C.L.A. Conference Birmingham 1989
contact lenses immersed in a cleaning tank are claimed to benefit from boundary or surface cavitation. The microbiological action of ultrasound arises by three mechanisms: 1
The purely mechanical strain put on the cell wall by the sudden application, and the equally sudden release of pressure. 2. The cavitation effect of fluid within the cell. 3. The rise in temperature produced by ultrasound. Although little evidence exists in the literature, and some of this provides conflicting evidence, it can be stated that (Peterson G.L. (1977)) 1. Efficacy of anti-microbial activity is more related to the intensity of the wave emission than to its frequency. 2. Cavitation becomes more difficult and less intense as the frequency is increased, thus requiring a higher power input to produce any effect. These points therefore place a limitation on the manufacturer of patient units where size, weight, cost and heat generation must all be balanced against the desired cleaning and anti-microbial activities. For these reasons and also because of the small volume of material that can be treated at any one time, ultrasound has found little application in convention microbiology and little published data therefore exists on the subject. From the practitioner's point of view many questions need to be asked regarding ultrasound since the ramifications go beyond that of simple cleaning and antimicrobiological activity. Some of these include:-1. Are they microbiologically effective. 2. Do they function safely with non-preserved or only preserved solutions? 3. Are the units reliable? 4. What is the life of the units? 5. Do they clean and, if so, how significant is this? 6. What are the ideal ultrasound frequency and intensity levels? 7. Are enzyme and other clean actions enhanced? 8. Are they safe electrically? 9. Are special solutions preferable i.e preserved and/or plus surfactants? 10. Is lens life shortened (because of the heat) or increased (because of better cleaning) by ultrasound? 11. What will be the impact on the present ancillary product market?
Method
A. Microbiological Cell suspensions of Pseudomonas aeruginosa ATCC 27853 and Candida albicansATCC 10231 were used to test the disinfection capabilities of the ultrasonic unit. Stock cultures of Ps. aeruginosa and C. albicans were inoculated into Tryptic Soy Broth (Difco Laboratories)
Transactions of B.C.L.A. Conference Birmingham 1989
and incubated for 24 hours at 36°C, subcultured and tested for purity. The cell culture was centrifuged at 2000rpm for 10 minutes. The supernatant was decanted off and the cell pellet resuspended in phosphate buffered saline. This procedure was repeated twice, to obtain a saline suspension of fresh cells of Ps. aeruginosa and C.
albicans. The efficacy of the ultrasound unit against Ps. aeruginosa was tested for all 3 cycles of the unit, and with C. albicans with the 2 soft contact lens cycles. Contact lenses were used in situ in all the tests. With the hard lens cycle Polycon HDK lenses were used. CSI lenses were in the soft, low water content cycle and experimental 75 % water content lenses used for the soft, high water cycle. When the unit was tested against Ps. aeruginosa a second test was performed with the addition of an organic soil. For each test, the sterile lenses were added to the clean dry sonification unit 3.5ml of sterile Gelflex Normal Saline was pipetted into the unit. 10~1 of the cell suspensions was added. The solution was mixed with a pipette and 0.5ml removed for enumeration.
Reliability The manufacturer's claims for the temperatures produced by the unit were determined using a thermocouple inserted through the lid of the unit into the saline bath. The average of three cycles of a single unit were measured.
B. Cleaning Three HEMA lens wearers with identical prescription lenses were asked to perform the following cleaning procedures over a three month period: One lens, selected by the patient, was to be surfactant cleaned for twenty seconds, rinsed with saline, and then stored in preserved saline overnight. No enzymatic treatment was to be used. The other lens was to be similarly surfactant cleaned, placed in the Sonasept Unit in unpreserved saline, and then subjected to the Soft Low Water cycle procedure. After three months both lenses were subjected to protein extraction and measurement utilising a modified Lowry procedure (Peterson W.L. (1977). In order to compare the relative efficacy of any cleaning/protein removal produced by the unit a further test was carried out. Seventeen HEMA lenses of identical parameters were soaked in an artificial tears solution for twelve hours, boiled for fifteen minutes, resoaked for a further twelve hours, and re-boiled again for twelve hours. Five lenses were used as a control group; six were cleaned for twenty seconds using the surfactant cleaner LC65 and rinsed with saline; and six were cleaned with the surfactant cleaner, rinsed, soaked for two hours in papain enzymatic cleaner, and finally surfactant cleaned again for twenty seconds and rinsed. Protein was then extracted from the lenses by the modified Lowry procedure.
21
Results
A. Micngbiological These are shown in Table 1. It can be seen that only the 'Soft Low Water' cycle produced lens disinfection with bacterial and fungal survival at both the other two cycles. It would appear, therefore, that the units are unable to kill microorganisms by means of ultrasound and function simply as low heat units.
enzymatic cleaning. The enzymatic cleaner removed an additional 30% of protein following surfactant cleaning alone. Table 2: Protein removal by daily use of the Sonasept
Unit, Low Water Soft setting. Micrograms Protein Removal After Three Months Patient
Surfactant Cleaned Lens
Surfactant Cleaned + Ultrasonic Cleaning
JS DW JD Test 1" Test 2
92.00 89.2 40.4 86.3
56.3 55.0 30.0 58.7
Table 1: Bacterial and fungal counts before and after
Sonasept treatment in unpreserved saline.
Before After D Value
HARD LENS CYCLE 45°C for 12' --org. soil +org. soft 6.5 x 108 6.3 x 108 3 × 106 1.5 x 106 5.14 6.60 minutes
Before After
SOFT LOW CYCLE 1.14 X 108 No Growth
* The patient split one lens after one month. Both lenses were replaced for the remainder of the test period.
Before After
SOFT H I G H CYCLE 3.6 × 107 Heavy Growth
cleaning alone and surfactant cleaning plus a single proteolytic enzymatic treatment.
SOFT LOW WATER CYCLE 65 ° for 45'
Group 1 (control)
Ps. aeruginosa
77.0
__+24.5
Before After
1.3 X 106 (SD q- 0.3 X 106) No Growth SOFT H I G H WATER CYCLE 45*C for 45' 0.7 X 106 (SD -+- 0.1 X 106) 1.6 X 106 (SD + 0.2 X 10 6) No Change
+13.4
Table 3: In-vitro protein removal comparing surfactant
Group 2 (surfactant only)
C. albicans Before After
50.0
Group 3 (surfactant + enzyme)
Micrograms Protein Extracted From Lenses 52.4 50.5 48.0 57.5 55.8 52.8
27.6 29.4 26.2 34.8 22.7 26.5 _+3.9
29.5
16.5 18.9 22.0 2.8 21.5 23.7 +3.4
20.7
+2.6
Reliabifity The following cycle times and temperatures were recorded: High Water Content Lens Setting -45°C for 25 minutes (45°C for 45 minutes claimed); Low Water Content Lens Setting -65°C for 17 minutes (65°C for 20 minutes claimed); Hard Lens Setting -45°C for 5 minutes (as claimed).
B. Cleaning This is shown in Tables 2 and 3. No subjective differences between the two lenses could be detected by any of the three patients using the ultrasonic cleaner. Protein extraction showed that all three lenses had been cleaned with an average of 35% of protein removed by the additional (to surfactant cleaning) ultrasonic process. Table 3 shows that approximately 60% of lens protein was removed by the combination of surfactant plus
22
Discussion In this preliminary report it has only proven possible to look at one unit currently marketed and to tentatively answer only some of the questions raised at the beginning of the talk. Of the single unit measured the time-temperature cycle was only accurate for the Hard Lens Setting; close for the Low Water Soft Lens Setting; and considerably out for the High Water Setting. This may conceivably be an isolated faulty unit but since neither patients nor practitioners have the means to test these functions the responsibility must lie with the manufacturer to produce consistent accuracy. Microbiologically the unit only functioned safely at the Low Water Soft setting. This is the highest temperature setting achieved by the unit and would appear to indicate that the unit functions in its antimicrobial activity simply as a low heat unit and not by utilisation of ultrasonics. Since low heat units function at 70°C and above, and this figure is generally accepted as being the lowest
Transactions of B.C.L.A. Conference Birmingham 1989
acceptable by microbiological standards, then there is no room for any safety margin even at the LWC Soft setting. Microbiological safety could be enhanced by using preserved saline or hydrogen peroxide in the unit but this defeats the cost advantages of the unit using unpreserved saline and may introduce the problem of preservation sensitivity. Table 2 shows that all three lenses tested in the in-vivo situation for protein removal by the Sonasept Unit showed approximately 35% reduction in protein build up compared to the non-ultrasonically cleaned contralateral eye. Thus the manufacturer's claims that ultrasonic cleaning reduces surface deposition can be confirmed. However, if this is compared to protein removal by conventional methods then in-vitro testing showed that a single proteolytic enzymatic treatment removed an additional 30% surface protein after surfactant cleaning with surfactant cleaning and protease treatments combined removing a total of 60% protein. Regular protease treatment is therefore likely to remove considerably more protein than ultrasonic treatment by the unit under test. Other ultrasonic units marketed may perform better than the one utilised in these tests. Indeed the concept holds definite promise for the future. Specific uses may also be developed by practitioner as well as the patient. For example Liprofin (Alcon) functions optimally at 60°C. Might it work even more efficaciously combined with ultrasonics at the LWC setting? Kerr (198 8) has reported that the alcohol-based cleaner, Miraflow (Cooper), is effective at removing lens calculi. This is shown to be very effective by comparing Figures 2(a) and (b).
/i
Specific cleaners and/or solutions or the advent of more efficient ultrasonic units may change dramatically the role of these units. Other disadvantages of ultrasonic units have been cited, 1. Reports have emerged that certain high water content lenses e.g Permalens, Permaflex and Lunelle have occasionally turned permanently opaque following ultrasound cleaning (Stewart P.A. (1988)). Possible causes inlude: (a) depolymerisation or conversely further cross-linking. (b) phase separation in a polymer blend e.g NVP co-
Transactions of B.C.L.A. Conference Birmingham 1989
Fig 2b.
polymerised with MA produces a co-polymer comprised of polymer 'fractions' of varying composition and hence varying refractive index. These 'fractions' may tend to separate into semi-discrete phases under the influence of the ultrasound and thereby render the lens opaque. 2. Although microbiologically ultrasound enhances the activity of hydrogen peroxide the French ~quasteril' unit instruction leaflet states that using their unit (which combines ultrasound with ultraviolet light) will turn lenses cloudy that have been used with any oxidising disinfection system prior to ultrasound + U V teatment. Presoaking in unpreserved saline for 72 hours prior to first using the unit is recommended. Conclusion Initial trials of the Sonasept Ultrasonic Patient Unit showed it is microbiologically unsafe at the Hard and High Water (HWC) Soft settings. The unit is considered only marginally safe even at the Low Water Soft (LWC) setting. At the HWC setting one unit tested only remained at the cleaning/disinfection cycle for just over half of the claimed time. In-vivo testing showed that approximately 35% of surface protein was removed after three months by daily ultrasound by a single protease treatment presumably indicating that regular protease treatment would be more efficient and significantly lens expensive. Some high water content (PVP containing?) lenses have been reported to turn opaque after ultrasound treatment. Specific uses such as Miraflow or Liprofin treatments may be useful to the practitioner in conjunction with ultrasound. The possibility also exists of enhanced enzymatic activity with heat resistant enzymes. It should be emphasised that this report is of only a preliminary nature; has involved the testing of only one type of ultrasonic unit; and has only involved small patient numbers. The project is ongoing. References RoetzheimW. Personalultrasoniccontactlenscleaning. C L. Spectrum 1987: January 29-38. FetersonG.L. A simplificationof the protein assaymethodof Lowryet al. which is generallymore applicable. Anal Biochem 1977; 83: 346-356. Kerr C. (1988) Decontaminating lenses. Optician, Vol 195. No.5129. p.29.
23
Ultrasonic Cleaning (modified after Roetzheim @ )
ULTRASOUND INTENSITY
Metal Welding ] & cutting Destructive ",~ Metal Etching !
~ , P a i n t Stripping
~
Introduction
Practitioner and patient disenchantment with current contact lens cleaning products due to reasons of cost, complexity, adverse reactions, availability, inadequate performance, etc., have led to examination of alternative systems. The search for a simple, fool-proof system that provides both a cleaning and disinfection action has led to the recent introduction of portable, patient ultrasonic units. As little is known about such units, and because recent reports and claims have been made in the lay press and on television, this preliminary report has been written to aid practitioners in their understanding of the system and to provide initial research data. The advantage claimed for patient ultrasonic units are:-1. Increased lens life because of reduced deposit formation. 2. Increased comfort due to a maintained clean surface. 3. Effective anti-microbiological action 4. No toxic or allergic reaction to the preservatives or Anthony J. Phillips, P. Badenoch & C. Copley, The Flinders Contact Lens Research Group of South Australia.
20
Acceleration of Non chemical destructive ~ reactions
Ideal level for contact < lens cleaning and disinfection
Fault detection
Ultrasonic devices may be divided into destructive or non-destructive devices, (Roetcheim, W. 1979) the former designed to alter the media in which the waves are formed and the latter not altering the media. Figure 1 shows that ultrasonic contact lens cleaners exist at the border of destructive and non-destructive devices, that is, the unit must be powerful enough to remove contaminants and produce lens disinfection, but gentle enough to avoid harming the lens material. The cleaning action of ultrasonic units is produced by a process known as cavitation. The ultrasound waves produced by the transducers in the unit produce frictional forces within the liquid medium. This produces both heat and the liberation of microscopic bubbles. These bubbles re-dissolve almost immediately producing an implosion or 'cavitation' effect. Because most cavitation occurs at, or very close to, solid surfaces,
Transactions of B.C.L.A. Conference Birmingham 1989
contact lenses immersed in a cleaning tank are claimed to benefit from boundary or surface cavitation. The microbiological action of ultrasound arises by three mechanisms: 1
The purely mechanical strain put on the cell wall by the sudden application, and the equally sudden release of pressure. 2. The cavitation effect of fluid within the cell. 3. The rise in temperature produced by ultrasound. Although little evidence exists in the literature, and some of this provides conflicting evidence, it can be stated that (Peterson G.L. (1977)) 1. Efficacy of anti-microbial activity is more related to the intensity of the wave emission than to its frequency. 2. Cavitation becomes more difficult and less intense as the frequency is increased, thus requiring a higher power input to produce any effect. These points therefore place a limitation on the manufacturer of patient units where size, weight, cost and heat generation must all be balanced against the desired cleaning and anti-microbial activities. For these reasons and also because of the small volume of material that can be treated at any one time, ultrasound has found little application in convention microbiology and little published data therefore exists on the subject. From the practitioner's point of view many questions need to be asked regarding ultrasound since the ramifications go beyond that of simple cleaning and antimicrobiological activity. Some of these include:-1. Are they microbiologically effective. 2. Do they function safely with non-preserved or only preserved solutions? 3. Are the units reliable? 4. What is the life of the units? 5. Do they clean and, if so, how significant is this? 6. What are the ideal ultrasound frequency and intensity levels? 7. Are enzyme and other clean actions enhanced? 8. Are they safe electrically? 9. Are special solutions preferable i.e preserved and/or plus surfactants? 10. Is lens life shortened (because of the heat) or increased (because of better cleaning) by ultrasound? 11. What will be the impact on the present ancillary product market?
Method
A. Microbiological Cell suspensions of Pseudomonas aeruginosa ATCC 27853 and Candida albicansATCC 10231 were used to test the disinfection capabilities of the ultrasonic unit. Stock cultures of Ps. aeruginosa and C. albicans were inoculated into Tryptic Soy Broth (Difco Laboratories)
Transactions of B.C.L.A. Conference Birmingham 1989
and incubated for 24 hours at 36°C, subcultured and tested for purity. The cell culture was centrifuged at 2000rpm for 10 minutes. The supernatant was decanted off and the cell pellet resuspended in phosphate buffered saline. This procedure was repeated twice, to obtain a saline suspension of fresh cells of Ps. aeruginosa and C.
albicans. The efficacy of the ultrasound unit against Ps. aeruginosa was tested for all 3 cycles of the unit, and with C. albicans with the 2 soft contact lens cycles. Contact lenses were used in situ in all the tests. With the hard lens cycle Polycon HDK lenses were used. CSI lenses were in the soft, low water content cycle and experimental 75 % water content lenses used for the soft, high water cycle. When the unit was tested against Ps. aeruginosa a second test was performed with the addition of an organic soil. For each test, the sterile lenses were added to the clean dry sonification unit 3.5ml of sterile Gelflex Normal Saline was pipetted into the unit. 10~1 of the cell suspensions was added. The solution was mixed with a pipette and 0.5ml removed for enumeration.
Reliability The manufacturer's claims for the temperatures produced by the unit were determined using a thermocouple inserted through the lid of the unit into the saline bath. The average of three cycles of a single unit were measured.
B. Cleaning Three HEMA lens wearers with identical prescription lenses were asked to perform the following cleaning procedures over a three month period: One lens, selected by the patient, was to be surfactant cleaned for twenty seconds, rinsed with saline, and then stored in preserved saline overnight. No enzymatic treatment was to be used. The other lens was to be similarly surfactant cleaned, placed in the Sonasept Unit in unpreserved saline, and then subjected to the Soft Low Water cycle procedure. After three months both lenses were subjected to protein extraction and measurement utilising a modified Lowry procedure (Peterson W.L. (1977). In order to compare the relative efficacy of any cleaning/protein removal produced by the unit a further test was carried out. Seventeen HEMA lenses of identical parameters were soaked in an artificial tears solution for twelve hours, boiled for fifteen minutes, resoaked for a further twelve hours, and re-boiled again for twelve hours. Five lenses were used as a control group; six were cleaned for twenty seconds using the surfactant cleaner LC65 and rinsed with saline; and six were cleaned with the surfactant cleaner, rinsed, soaked for two hours in papain enzymatic cleaner, and finally surfactant cleaned again for twenty seconds and rinsed. Protein was then extracted from the lenses by the modified Lowry procedure.
21
Results
A. Micngbiological These are shown in Table 1. It can be seen that only the 'Soft Low Water' cycle produced lens disinfection with bacterial and fungal survival at both the other two cycles. It would appear, therefore, that the units are unable to kill microorganisms by means of ultrasound and function simply as low heat units.
enzymatic cleaning. The enzymatic cleaner removed an additional 30% of protein following surfactant cleaning alone. Table 2: Protein removal by daily use of the Sonasept
Unit, Low Water Soft setting. Micrograms Protein Removal After Three Months Patient
Surfactant Cleaned Lens
Surfactant Cleaned + Ultrasonic Cleaning
JS DW JD Test 1" Test 2
92.00 89.2 40.4 86.3
56.3 55.0 30.0 58.7
Table 1: Bacterial and fungal counts before and after
Sonasept treatment in unpreserved saline.
Before After D Value
HARD LENS CYCLE 45°C for 12' --org. soil +org. soft 6.5 x 108 6.3 x 108 3 × 106 1.5 x 106 5.14 6.60 minutes
Before After
SOFT LOW CYCLE 1.14 X 108 No Growth
* The patient split one lens after one month. Both lenses were replaced for the remainder of the test period.
Before After
SOFT H I G H CYCLE 3.6 × 107 Heavy Growth
cleaning alone and surfactant cleaning plus a single proteolytic enzymatic treatment.
SOFT LOW WATER CYCLE 65 ° for 45'
Group 1 (control)
Ps. aeruginosa
77.0
__+24.5
Before After
1.3 X 106 (SD q- 0.3 X 106) No Growth SOFT H I G H WATER CYCLE 45*C for 45' 0.7 X 106 (SD -+- 0.1 X 106) 1.6 X 106 (SD + 0.2 X 10 6) No Change
+13.4
Table 3: In-vitro protein removal comparing surfactant
Group 2 (surfactant only)
C. albicans Before After
50.0
Group 3 (surfactant + enzyme)
Micrograms Protein Extracted From Lenses 52.4 50.5 48.0 57.5 55.8 52.8
27.6 29.4 26.2 34.8 22.7 26.5 _+3.9
29.5
16.5 18.9 22.0 2.8 21.5 23.7 +3.4
20.7
+2.6
Reliabifity The following cycle times and temperatures were recorded: High Water Content Lens Setting -45°C for 25 minutes (45°C for 45 minutes claimed); Low Water Content Lens Setting -65°C for 17 minutes (65°C for 20 minutes claimed); Hard Lens Setting -45°C for 5 minutes (as claimed).
B. Cleaning This is shown in Tables 2 and 3. No subjective differences between the two lenses could be detected by any of the three patients using the ultrasonic cleaner. Protein extraction showed that all three lenses had been cleaned with an average of 35% of protein removed by the additional (to surfactant cleaning) ultrasonic process. Table 3 shows that approximately 60% of lens protein was removed by the combination of surfactant plus
22
Discussion In this preliminary report it has only proven possible to look at one unit currently marketed and to tentatively answer only some of the questions raised at the beginning of the talk. Of the single unit measured the time-temperature cycle was only accurate for the Hard Lens Setting; close for the Low Water Soft Lens Setting; and considerably out for the High Water Setting. This may conceivably be an isolated faulty unit but since neither patients nor practitioners have the means to test these functions the responsibility must lie with the manufacturer to produce consistent accuracy. Microbiologically the unit only functioned safely at the Low Water Soft setting. This is the highest temperature setting achieved by the unit and would appear to indicate that the unit functions in its antimicrobial activity simply as a low heat unit and not by utilisation of ultrasonics. Since low heat units function at 70°C and above, and this figure is generally accepted as being the lowest
Transactions of B.C.L.A. Conference Birmingham 1989
acceptable by microbiological standards, then there is no room for any safety margin even at the LWC Soft setting. Microbiological safety could be enhanced by using preserved saline or hydrogen peroxide in the unit but this defeats the cost advantages of the unit using unpreserved saline and may introduce the problem of preservation sensitivity. Table 2 shows that all three lenses tested in the in-vivo situation for protein removal by the Sonasept Unit showed approximately 35% reduction in protein build up compared to the non-ultrasonically cleaned contralateral eye. Thus the manufacturer's claims that ultrasonic cleaning reduces surface deposition can be confirmed. However, if this is compared to protein removal by conventional methods then in-vitro testing showed that a single proteolytic enzymatic treatment removed an additional 30% surface protein after surfactant cleaning with surfactant cleaning and protease treatments combined removing a total of 60% protein. Regular protease treatment is therefore likely to remove considerably more protein than ultrasonic treatment by the unit under test. Other ultrasonic units marketed may perform better than the one utilised in these tests. Indeed the concept holds definite promise for the future. Specific uses may also be developed by practitioner as well as the patient. For example Liprofin (Alcon) functions optimally at 60°C. Might it work even more efficaciously combined with ultrasonics at the LWC setting? Kerr (198 8) has reported that the alcohol-based cleaner, Miraflow (Cooper), is effective at removing lens calculi. This is shown to be very effective by comparing Figures 2(a) and (b).
/i
Specific cleaners and/or solutions or the advent of more efficient ultrasonic units may change dramatically the role of these units. Other disadvantages of ultrasonic units have been cited, 1. Reports have emerged that certain high water content lenses e.g Permalens, Permaflex and Lunelle have occasionally turned permanently opaque following ultrasound cleaning (Stewart P.A. (1988)). Possible causes inlude: (a) depolymerisation or conversely further cross-linking. (b) phase separation in a polymer blend e.g NVP co-
Transactions of B.C.L.A. Conference Birmingham 1989
Fig 2b.
polymerised with MA produces a co-polymer comprised of polymer 'fractions' of varying composition and hence varying refractive index. These 'fractions' may tend to separate into semi-discrete phases under the influence of the ultrasound and thereby render the lens opaque. 2. Although microbiologically ultrasound enhances the activity of hydrogen peroxide the French ~quasteril' unit instruction leaflet states that using their unit (which combines ultrasound with ultraviolet light) will turn lenses cloudy that have been used with any oxidising disinfection system prior to ultrasound + U V teatment. Presoaking in unpreserved saline for 72 hours prior to first using the unit is recommended. Conclusion Initial trials of the Sonasept Ultrasonic Patient Unit showed it is microbiologically unsafe at the Hard and High Water (HWC) Soft settings. The unit is considered only marginally safe even at the Low Water Soft (LWC) setting. At the HWC setting one unit tested only remained at the cleaning/disinfection cycle for just over half of the claimed time. In-vivo testing showed that approximately 35% of surface protein was removed after three months by daily ultrasound by a single protease treatment presumably indicating that regular protease treatment would be more efficient and significantly lens expensive. Some high water content (PVP containing?) lenses have been reported to turn opaque after ultrasound treatment. Specific uses such as Miraflow or Liprofin treatments may be useful to the practitioner in conjunction with ultrasound. The possibility also exists of enhanced enzymatic activity with heat resistant enzymes. It should be emphasised that this report is of only a preliminary nature; has involved the testing of only one type of ultrasonic unit; and has only involved small patient numbers. The project is ongoing. References RoetzheimW. Personalultrasoniccontactlenscleaning. C L. Spectrum 1987: January 29-38. FetersonG.L. A simplificationof the protein assaymethodof Lowryet al. which is generallymore applicable. Anal Biochem 1977; 83: 346-356. Kerr C. (1988) Decontaminating lenses. Optician, Vol 195. No.5129. p.29.
23