CET Contact Lens Monthly

his is part 2 of two CET articles looking at the state- of-play in the lens care Contact lens care field and looks at the latest product developments, solution ingredients and Part 2 – Latest developments Tformulations. Part 1 has already set the scene by looking at the current thinking Nick Atkins concludes his series looking at care systems with a and likely improvements that could be revision of the latest developments in lens care. Module C15770, made to the regulation and testing of contact lens solutions. one CL point for CLOs, one general CET point for optometrists Are you still supplying your solution and dispensing opticians starter kit based on what is in the cupboard and nearest to hand at the Table 1 time? Hopefully not, but this article is Examples of single multipurpose solution formulations past intended to help clinicians review what and present they use against the latest products available, in order to formulate a Product Manufacturer Disinfectant Conc’n Surfactant Additional strategy for the solutions they stock and (ppm) lubricant/ then consider which is most appropriate conditioners for each of the individual patient and ReNu B+L PHMB 0.5 Poloxamine None lens combinations in the chair. Focus CIBA Vision PHMB 1.0 Pluronic Dexpathenol It is now more than 16 years since Aqua F127 the introduction of multipurpose Complete AMO PHMB 1.0 Poloxamer None contact lens solutions in the UK with Easy Rub 237 the historic launch of Complete and All in One Sauflon PHMB 5.0 Poloxamine None ReNu – in the summer of 1994. The Opti-1 Alcon Polyquad 11.0 None None switch from Medicine Control Agency to Medical Devices Agency (now the MHRA) control, with the introduction of CE marking from January 1 1995, By the middle of the last decade, neutralisation period with the one-step resulted in a flood of lens care solution practitioners had almost performed a products, clearly peroxide is not the introductions. The UK’s first one-step complete turnaround in their prescribing definitive answer. Also, as mentioned , AOSept, was one habits, from a market dominated by in Part 1 of this series, reports of solution that benefited from the change one- and two-step hydrogen peroxide Acanthamoeba kerititis in the UK have in regulatory control and for the next 10 systems. According to the annual review been in decline during the same period years or so there were two basic types of of UK practitioner prescribing trends of MPS growth and market dominance, ‘simpler’ systems dominating in varying by Eurolens Research in 2005,1 the use which is unlikely to be coincidental. proportions – the one-step peroxide and of multipurpose solutions peaked at 91 the multipurpose solutions. per cent of care products recommended All solutions are NOT the same by practitioners. There was a slight Over the past seven years, there have Multipurpose vs hydrogen dip in this figure subsequently, with been many reformulations and new peroxide multipurpose solutions recovering claims of advanced cleaning and During the mid to late 1990s the to 89 per cent of care products enhanced comfort. However, until principal debate as to which was the recommended by practitioners in the 2004 the basic chemicals involved best solution focused on MPS versus 2010 survey.2 It is likely that events in the preservation and disinfection peroxide, but there was also the parallel such as the product withdrawals due to process had remained unchanged. discussion as to which product was infection outbreaks as well as concerns With the proliferation of silicone best within these two categories. In about staining levels with certain lens/ hydrogel lenses offering patients the peroxide category, was one-step solution combinations might have led improved ocular health and prolonged as efficacious as two-step and in the some practitioners to increase their comfort and many practitioners multipurpose solution (MPS) sector use of peroxide-based systems. It is reluctant to prescribe patients a was polyquarternium-1 (polyquad) important to remember, however, that continuous wear modality, it is better than polyhexinide? Increasingly, no system is a panacea and that each reasonable to assume that the future particularly as we entered this century, case needs to be judged on its merits. for many wearers is to upgrade their the debate became more centred on Certainly MPSs would not have come hydrogel lenses and continue with daily the MPS category with the numerous to dominate the market if they did not wear and lens care. It should therefore polyhexinide formulations versus have significant advantages for both be remembered that most solutions in polyquad still the only protagonists. patient and practitioner. common use today were developed Polyhexanide is used most extensively While peroxide is effective against a before the advent of silicone hydrogel in a variety of different companies’ large number of strains of Acanthamoeba materials and so seamless compatibility formulations; polyquad, until a few trophozoites and cysts, it requires a long between lens and care system is perhaps months ago, was only available in Alcon soaking time which many wearers a naive expectation. Laboratories’ products such as Optifree will only find convenient if left in 3 Despite many solutions appearing to Express and Optifree Replenish. Table 1 per cent peroxide overnight. With no be similar, those that read the research shows examples of the basic formulation major manufacturer offering a two-step will understand that no one solution is of a historic sample of these solutions. peroxide and a minimum four-hour the same as another. A delicate balance

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exists between the ingredients in a Table 2 solution formulation and the interaction Composition of Regard multipurpose solution of that formulation with different lens materials and the deposits that can form Components Action on those different lenses. NaCLO2 Disinfection ‘New generation’ preservatives H2O2 Stabilisation/ Early this decade the debate as to the re-activation of best solution focused on the MPS disinfection category and whether polyhexanide or Pluronic F-68 Cleaning/ polyquad was superior as a disinfectant. lubrication They reigned supreme until 2004 when Hydroxypropylmethylcellulose Lubrication two new preservation systems, sodium Figure 1 Sodium chlorite was first seen in chlorite and alexidine, challenged the Regard MPS preservation and disinfection status quo widening the debate. lens disinfection and until last autumn safely for many years as a treatment it could only be found in Alcon for municipal drinking water. Sodium Polyhexanide solutions. With a molecular weight chlorite generates chlorine dioxide Also known as polyhexymethylene of 5,000 it resists diffusion into the which is very effective in killing biguinide (PHMB), polyaminopropyl lens matrix, minimising the toxic Gram+ and Gram- bacteria, yeasts and biguinide (PAPB) and commercially hypersensitivity reactions found with fungi, subsequently breaking down as Dymed in the original MPS, ReNu the traditional smaller preservatives into the components of natural tears – from Bausch+Lomb, polyhexinide was such as and . salt, water and oxygen. one of the first of the so-called ‘new Originally used in isolation in Optifree, The chlorite/peroxide complex in generation’ preservatives. its relatively poor performance against Regard is an active anti-microbial agent Polyhexinide is a biguinide, belonging fungus and Acanthamoeba was addressed and is safe and non-irritating to the to the same pharmaceutical family as by its formulation with MAPD corneal epithelium.4 The formulation chlorhexidine. However, it differs in (myristamidipropyl dimethylamine), is based on the synergistic microbial that it is long chain polymer (molecular commercially known as Aldox, with activities of both chemicals and once weight of 1,300 compared to the 359 the introduction of Optifree Express.3 the contact lenses are removed from of chlorhexidine) with 6-8 active sites. the solution (which maintains stability) These bind to phospholipids in the Sodium chlorite sodium chlorite breaks down into cytoplasmic membrane disrupting it, Sodium chlorite was first seen in a MPS sodium chloride and oxygen.5 causing loss of the cell constituents when Regard (Figure 1) was presented, and cell death. Polyhexanide has been via a poster at the BCLA meeting in Alexidine widely used in varying concentrations May 20034 and has subsequently been In late 2004 Bausch+Lomb (B+L) from 0.00005 per cent to 0.0005 per employed by Sauflon in its Synergy launched ReNu with MoistureLoc. cent as shown in Table 1. product. Regard came to the attention, It was marketed on the benefits of interest and use of the author due to its moisture-retaining properties, but Polyquad its claimed ‘preservative free’ method many practitioners will have missed the A polymeric quarternary ammonium of disinfection. The key components of most important aspect of the solution compound, Polquarternium-1, to give Regard can be seen in Table 2. – the introduction of a brand new it its chemical name, is the largest Sodium chlorite is activated by acidic disinfectant to the contact lens sector, polymeric molecule used for contact cellular components and has been used namely alexidine. Alexidine has a track record in the Table 3 mouthwash industry in the same Examples of dual disinfectant multipurpose solution formulations way as polyhexanide was ‘borrowed’ from its use in swimming pools and Product Manufacturer Conc’n Surfactant Additional is also from the same biguinide family (ppm) lubricant/ of disinfectants. However there are conditioners differences between alexidine and Biotrue Bausch+Lomb PHMB 1.3 Poloxamine Hyaluronic Acid polyhexanide. Alexidine, a bis-bigunide, 1.0 (Tetronic 1107) is a smaller molecule that contains two Polyquad active sites. Similar to polyhexanide, Complete Abbot Alexidine 1.6 Poloxamine None these biguinide groups interact with RevitaLens Medical (Tetronic 904) and disrupt the acidic phospholipid Optics Polyquad 3.0 groups in a micro-organism Opti-Free Alcon Polyquad 11.0 5.0 Poloxamine Aminomethyl- cytoplasmic membrane; the membrane Express (Tetronic 1304) propanol disintegrates and the cell components Aldox* are released. Alexidine can now be Opti-Free Alcon Polyquad 11.0 Poloxamine nonanoyl found in Complete RevitaLens and so Replenish (Tetronic 1304) ethylene-diami- it is important to realise that alexidine Aldox* 5.0 netriacetic acid was never implicated in the global (Tearglyde) withdrawal of ReNu with MoistureLoc. The outbreak of Fusarium keratitis, *Myrisamidopropyl dimethylamine mainly in Asia Pacific, was largely due to non-compliance and the protection

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Table 4 Composition of Biotrue and Complete RevitaLens multipurpose solutions

Biotrue Complete RevitaLens Preservatives PHMB 0.00013% 0.00016% alexidine 0.0001% polyquaternium-1 0.0003% polyquaternium-1 Buffer Boric acid; sodium borate Sodium borate; boric acid Chelating agent EDTA (%?) 0.05% EDTA Surfactant/ Poloxamine (Tetronic 1107) Tetronic 904 wetting agents Other Hyaluron (hyaluronic acid – Trisodium citrate glycosaminoglycan) sulfobetaine (zwitterionic detergent) Figure 2 AMO’s Complete RevitaLens and Biotrue by B+L afforded to the fungi by the synthetic Table 5 take different approaches to their ‘biofilm’ left in lens cases, largely due to formulations. A more detailed review of MPS containing hyaluronic acid a combination of evaporation and the their ingredients is shown in Table 4. topping up of the solution in the case. Solution Name Disinfectant Company Other additives Dual disinfectants Biotrue PHMB/Polyquad Bausch+Lomb Over the past decade there has been a Those as ‘experienced’ as the author Eyeye Imaxx PHMB No 7 great deal of research and development will remember the combined use of (All in One) into creating a contact lens solution chlorhexidine and thimerosal as dual Unica Sensitive PHMB Avizor that can enhance lens comfort and disinfectants, in varying concentrations, wearing time. The challenge is that in early chemical disinfecting solutions adding additional and arguably such as Hydrosoak from Contactasol. Optics (AMO) and B+L have recently non-essential ingredients complicates Chlorhexidine is more effective but has introduced solutions using a dual the formulation and inevitably results poor fungicidal capacity. Thimerosal disinfection approach similar to Alcon in compromises with other aspects of is slower acting but is known to be with its Optifree products. Table 3 the solution’s performance. To date, a more effective antifungal agent. It shows examples of the dual disinfecting manufacturers have used a variety of is interesting to note that following solutions currently available. surfactant and wetting agents, such the global withdrawal of one of AMO with Complete RevitaLens as hydroxypropylmethylcellulose their brands, both Abbot Medical and B+L with Biotrue (Figure 2) (HPMC), polyvinyl alcohol (PVA) and polyvinyl povidone (PVP) commonly found in dry eye drops. The cellulose- Multiple-choice questions – take part at opticianonline.net based agents such as HPMC are polysaccharides and so a potential Polyquarternium-1 is also known as: Which of these solutions is ‘preservative- food source for microorganisms, 1 4free’? which is why great care is taken in A Dymed A Optifree Replenish the formulation process. Recently a B PHMB B Synergy number of solutions have incorporated C Polyquad C Complete RevitaLens another polysaccharide used in dry eye D Polyhexinide D Biotrue preparations, namely hyaluronic acid (Table 5), in an attempt to improve the Regard contains: Polyhexanide has been commercially lens comfort enhancing effect during 2 5available in the following concentrations: lens storage. A Hydrogen peroxide A 50-500 ppm B Alexidine B 0.00005 per cent-0.0005 per cent Hyaluronic acid (HA) C MAPD C 5-50ppm HA, also known as sodium hyaluronate D Polyhexanide D 0.0005 per cent-0.005 per cent or hyaluronan, is a naturally occurring linear structured polysaccharide that Which of the following statements is true Which preservative has a molecular is found in the aqueous and vitreous 3about alexidine? 6weight of 5,000? humour and the synovial fluid of A It is borrowed technology from disinfecting A Alexidine joints. It is a non-toxic, viscoelastic, swimming pools B Polyhexanide biological polymer that has good B It has been used before in ReNu MultiPlus C Polyquad water binding properties to reduce C It demonstrates poor disinfection efficacy D Sodium chlorite evaporation. It also mimics the natural against Fusarium tear film in becoming more elastic D It is a small molecule with two active binding during the blink, increasing spreading sites and improving aqueous lubrication of the anterior ocular surface epithelial Successful participation in this module counts as one credit towards the GOC CET scheme tissues. This is known as rheological administered by Vantage and one towards the Association of Optometrists Ireland’s scheme. or non-Newtonian behaviour. The deadline for responses is March 3 2011 Importantly, and supporting its use in a contact lens solution, is the fact that

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HA has been shown to increase tear break-up time in adding the UV filter the chemist when used in eye drops.6 has to consider the impact of the filter compound on the water content. Discussion The most commonly used Contact lens solutions are quite complex formulations & UV-blocking compounds in and arguably more complex from a formulation QA standard hydrogels are known to perspective than most drugs. The latter are generally contact us be hydrophobic. Consequently, the formulated with only one objective, but contact lens …and let our panel of experts inclusion of these within the polymer solutions have to perform numerous functions and answer your queries matrix will have a natural tendency ultimately formulation is a balancing act derived to reduce the water content of the from compromise. resulting material. So if the material’s Unfortunately many practitioners, perhaps due to formulation is not readjusted to having no background in chemistry or microbiology, UV blocking and O2 maintain its final water content, then seem to rely more on the manufacturers for information Does the inclusion of an ultraviolet yes the oxygen permeability of the in this area than in any other area of contact lens Q filter affect the Dk of a soft or material will be impacted. However, practice; perhaps with this reliance on company data, gas-permeable contact lens? it is quite straightforward to re-adjust practitioners are also somewhat sceptical as to how the formulation in such a way as commercially biased this information is. Richard Ward replies: In to ensure the water content levels A considering the potential impact remain at the desired amount. Conclusion of the UV blocker on these two With gas-permeable contact lenses, A delicate balance exists between the contact lens material groups, it will be easier given that the oxygen permeability and its care system and the health of the ocular to deal with each material type is not related to water content but a surface in contact lens wear. Many practitioners separately. function of the silicon or fluorinated need to reconsider the priority they place on lens care Firstly, in adding a compound content of the formulations, the selection. Anyone who believes that all solutions are such as UV filters or blockers, it presence of another hydrophobic the same or similar are advised to take another look is important to recognise what compound within its formulation at the new products on the market and ensure that is required in obtaining a good may not be quite as dramatic. Again, they are familiar with the differences in their mode of acceptable lens material. The the material scientist will be able to action and formulations. The correct selection of lens development of such compounds is incorporate the UV filter compound care product has the potential to significantly improve all about balancing the final material’s within the material formulation and, the comfort and wearing times of many patients. properties through optimised through readjustment of the other Along with the appropriate selection of contact lens formulations. So for the material to main components, maintain the final material and modality, this will have an important be clinically acceptable, its overall material’s oxygen permeability. role to play in the long-term success of individual performance needs to show a balance So, in summary, yes the inclusion contact lens patients. between its bulk properties (modulus, of UV filters can have an impact on Ultimately it is the partnership between industry, strength, water content, transmission/ the material’s oxygen permeability government, practitioners and our patients, that will RI and Dk) and its surface characteristics, but it is possible to improve the balance between contact lens success and characteristics, such as wettability. minimise these effects by slight failure. The correct selection and use of lens care will When considering the effects of material formulation adjustments, continue to have significant impact on which group a UV on the different materials, I will especially as these filter compounds patient falls into, for many years to come. ● look at the standard (non-silicone) are usually present in relatively low hydrogels first. It is widely recognised formulation concentrations. References that the oxygen permeability (Dk) of 1 Morgan PB, Efron N. Trends in UK contact lens prescribing the material is entirely down to the ● Richard Ward is director technology 2005. Optician, 2005; 227(5950) 16-17. material’s water content and, as such, transfer at CooperVision UK 2 Morgan PB, Efron N. Trends in UK contact lens prescribing 2010. Optician, June 2010; 34-35. 3 Rosenthal RA, McAnally CL, McNamee LS, Buck SL et al. Broad spectrum antimicrobial activity of a new multipurpose disinfecting solution. CLAO J, 2000; 26:120-126. 4 Karageozian HL, Gates BW. Novel soft contact lens disinfection with Sodium Chlorite and Hydrogen Peroxide. 1993; Poster, BCLA Annual Clinical Conference. 5 Atkins N. Regard: A multipurpose solution. Optician, 2004: 228(5976):14-16. 6 Mengher LS, Pandher KS, Bron AJ & Davey CC. Effect of sodium hylaluronate (0.1 per cent) on break-up time (NIBUT) in patients with dry eyes. Br J Ophthalmol, 1986; 70: 442- 447.

● Nick Atkins is a contact lens optician and professional affairs/marketing consultant to the optical industry. He is What’s this? also a co-director of Proven Track Record, the force behind Answer to What’s this? (07.01.11): Independents Day and co-director of in-practice sales and The image shows threads trapped under a soft lens. On removal, the imprint of the training company Positive Impact. Atkins is a past president threads is seen more easily with fluorescein. The patient experienced no discomfort. of the British Contact Lens Association and a director on the The images are courtesy of Andrew Gasson board of the Association of British Dispensing Opticians opticianonline.net 04.02.11 Optician | 23