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26.3.7 Contact lens case

The contact lens case should be air-dried while lenses are worn. Ideally the case should be changed on a monthly basis. Unless it is boiled, there should be no contact with tap water in the hygiene regimen. This will avoid possible contamination with Acanthamoeba.4

PRACTICAL ADVICE

•Where papain causes an adverse reaction, especially with high water content lenses, reduce the soaking time to 15 minutes.

•Hydrogen peroxide breaks down residual papain and should be used after the enzyme cleaner.

•Advise hay fever sufferers to use them more frequently in the spring and early summer.

26.4 Solutions for rigid gas-permeable lenses

The surface of a rigid gas-permeable lens is more prone to deposits and interaction with some formulations of conditioning solutions compared to the more inert PMMA.

26.4.1 Wetting solutions

Wetting solutions were used on insertion to act as a cushion between the lens and cornea. They also enhanced the spread of tears across the lens surface, although the effect lasted only for a maximum of 15 minutes and sometimes for as little as 5 seconds.5

Formulation: tonicity agent; viscosity agent; wetting agent; preservatives; chelating agent.

26.4.2 Soaking solutions

Soaking solutions keep lenses hydrated during overnight storage in a sterile, bactericidal environment. They facilitate good surface wetting and assist the removal of deposits. Hydration is important to maintain the correct BOZR both for modern rigid lens materials and for PMMA over about −10.00 D.

Formulation: tonicity agent; wetting agent; detergent; preservatives; chelating agent.

26.4.3 Cleaning solutions

Cleaning solutions remove surface debris including lipids and mucus (e.g. TotalCare) and enhance the disinfecting action of the soaking solution. With the advent of fluorosilicon acrylates, greasing of the lens surface has become a more frequent problem. Manufacturers have therefore developed alcohol-based solutions (e.g. Boston Advance, Bausch & Lomb Elite, Miraflow) or cleaners with

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emollient and foam stabilizers (e.g. Total Care). The inclusion of microscopic polymeric beads in suspension gives a light surface polishing effect useful for removing denatured proteins (e.g. Boston, Bausch & Lomb).

Formulation: detergent; preservatives; chelating agent.

PRACTICAL ADVICE

•Advise patients to take care not to cause an inadvertent power change with the polishing action of cleaners with polymeric beads.

•Take care with cleaners containing only an organic solvent (e.g. isopropyl alcohol) to avoid upsetting the surface wetting properties of some rigid gas-permeable lens materials, especially fluoropolymers.

26.4.4 Multipurpose solutions

These combine all of the above functions but usually with some loss of efficiency. Cleaning may be particularly affected as, with no dedicated surfactant, stubborn deposits can form with some materials and patients.

•Wetting, soaking and cleaning (e.g. Boston Simplus).

•Soaking and cleaning.

•Wetting and soaking (e.g. Bausch & Lomb, Total Care).

Some reformulated wetting and soaking products are now called conditioning solutions (e.g. Boston Advance Comfort Formula).

Formulation: wetting agent; detergent; preservatives; chelating agent.

In rigid gas-permeable lens wearers, the use of a solution preserved with benzalkonium chloride (BAK), which has a low molecular weight, can, over a long period, give a sensitivity reaction. Typical symptoms are red, gritty eyes and reduced wearing time. This is much more of a problem with high Dk materials. The all-in-one solution Total, preserved with BAK, was reformulated to TotalCare for this reason. It now has three active ingredients:

•Croquat-L – a new conditioning agent that takes advantage of hydrogen bonding forming a hydrophilic layer on the surface of the lens.

•Hydroxyethylcellulose – a lubricant and viscosity agent to enhance comfort upon insertion.

•Polixetonium chloride – a cationic preservative with very low toxicity (to address the BAK issue).

Boston (Bausch & Lomb) was specifically formulated for the new generation of rigid lenses. It was one of the first products to make use of the concept of hydrogen bonding, where positively charged hydrophilic components anchor to negative sites on the lens surface, thus improving surface wetting.

Boston Advance is preserved with polyhexanide (PHMB) and chlorhexidine. This product uses half the concentration of chlorhexidine compared with the original formulation to address issues of toxicity and the binding of preservative to the lens surface. The other change is the introduction of additional conditioning agents which enhance the hydrogen bonding. The viscosity of the solution has been slightly reduced by the addition of polyethylene oxide but alterations

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to its formulation have reportedly increased retention of the solution on the lens surface, enhancing wettability.

If products are too viscous, they can lead to blurred vision following insertion. Some patients report their eyes feel sticky when they use such solutions and therefore use tap water or saline to rinse off any excess. Diluting the conditioning agent also dilutes the wetting and cushioning properties of the solution, removing many of the agents incorporated to improve lubricity. This reduces the conditioning benefits from the overnight soak by reducing the surface tension on the lens surface and can actually result in increased lens awareness.

26.4.5 Rewetting solutions (comfort drops)

Comfort drops are used to rewet lenses while they are worn, especially in dry environments (e.g. Blink Contacts).

Formulation: wetting agent; preservatives; chelating agent. Some are now produced without preservative in unit dose form (e.g. Refresh) or by a continuous monodose dispensing system (e.g. HycoSan).

26.4.6 Enzyme tablets

Proteinaceous films require enzyme removal with some rigid gas-permeable lens materials, particularly silicon acrylates. Weekly cleaning is recommended but monthly is the minimum suggested. Tablets are dissolved in saline. Liquid enzyme is also available, e.g. as a pancreatin based product. One drop is placed in the lens case with the disinfecting solution on a nightly basis (e.g. SupraClens); 0.4% sodium hypochlorite is also used as a protein remover (Progent A), neutralized by potassium bromide (Progent B). The soaking time is a maximum of only 30 minutes and the solutions are supplied as a unit dose preparation. The system also has powerful antimicrobial and prion efficacy (Menicon).

Formulation: (see Section 26.3.6).

PRACTICAL ADVICE

•Depending upon the active ingredient, patients find it much more convenient to leave lenses soaking overnight.

•Enzymes may not be required with fluoropolymers and rarely with CAB.

•Advise hay fever sufferers to use them more frequently in the spring and early summer.

26.4.7 Tap water

If the patient is a long-term user and has been regularly using tap water, suggest that rising mains water can be used to flush rigid gas-permeable lenses after cleaning and prior to overnight storage in a disinfecting solution. Although technically introducing a small risk of infection, many long-standing patients have used this procedure for several years. Tap water should not be used prior to insertion.

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26.4.8 Contact lens case

Boiled water or saline is safest for cleaning the lens case, which should then be air-dried. The case itself should be replaced at least every 6 months.

26.5 Compliance and product misuse

Although much attention is paid to the efficacy of soft lens disinfecting solutions, it is important to remember that good lens hygiene and compliance play a vital role in minimizing any risk of corneal infection. Compliance studies on lens care all lead to the same conclusion, that over 50% of lens wearers fail to follow instructions to a significant level.

Non-compliance stems from several factors including:

•Cost.

•Convenience.

•Apathy.

•Ignorance.

•Denial about the potential complications.

•Lack of proper instructions.

•Bad advice from friends and family.

Patients prefer less complex systems but there is doubt whether this leads to increased compliance. Patients tend to comply with the steps which affect comfort, such as a final saline rinse, but often disregard those aspects of lens hygiene which are most important for safety, such as digital cleaning and case hygiene.

The trend in rigid lens care is towards the use of multipurpose solutions. Instruction on proper use of these products is required in order to achieve optimal performance. Patients must clean and rinse their lenses immediately after removal and not as is common with many long-term rigid lens wearers prior to insertion. The lenses must then be placed in the case with sufficient volume of solution to cover both surfaces and left overnight to condition the surface of the lens. Lens insertion in the morning should consist of a fresh rinse with solution without additional cleaning or rinsing.

References

1.Jones L, Christie C. Soft contact lens solutions review: Part 2: Modern-generation care system. Optometry in Practice 2008;9:43–62.

2.Stehr-Green J. The epidemiology of Acanthamoeba keratitis in the United States.

American Journal of Ophthalmology 1989;107:331.

3.Fowler SA, Allansmith MR. Removal of soft lens deposits with surfactant – polymeric bead cleaner. Contact Lens Association of Ophthalmologists Journal

1984;10:229–31.

4.Seal DV, Dalton A, Doris, D. Disinfection of contact lenses without tap water rinsing: is it effective? Eye 1999;13:226–30.

5.Doane MG. In vivo measurement of contact lens wetting. Transactions of the British Contact Lens Association Annual Clinical Conference 1988;5:110–11.

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