Ever since soft hydrophilic contact lenses were first introduced in the 1970s, contamination has been a major concern. Generally, infectivity occurs during lens removal, lens care or lens storage. The earliest, and probably the most effective, disinfection system used heat to kill bugs. However, using an electrical device was inconvenient, particularly for those traveling. Concern over heating the proteins and soilants on the lenses led investigators to evaluate the use of anti-infective compounds—chemical substances that could be used to disinfect the contact lens without the use of heat. Early requirements involved looking at the rate of deactivation—or killing of a broad spectrum of organisms—combined with a simulated use test that required lenses to be contaminated with 100,000 to 1,000,000 organisms after the care cycle with no recoverable evidence on either the lens or in the care solution. The organisms that were selected were representative of a wide spectrum of potential contaminants: Pseudomonas aeruginosa, a water-born bacteria now recognized as the most likely to cause infections in contact lens wearers; Staph. epidermidis, a common skin bacteria; Serratia marcescens, a water-born bacteria; Candida albicans, a common yeast; and Aspergillis fumagatus, one of hardest molds to eliminate.¹

The First Dual Disinfectants
The idea of using more than one biocide in a dual disinfection system is not new. The earliest of the cold contact lens disinfecting solutions used two different biocides to achieve the efficacy necessary under the early disinfection requirements, which stressed no recovery of any organism from lenses, including the highly resistant mold, Aspergillis fumigatus. The early combination of chlorhexidine and thimerosal—e.g., Flexsol (Alcon) and Flex-Care (Alcon)—was used successfully with the earliest conventional hydrogel materials based on HEMA, and eventually classed as a Group 1 contact lens. These combinations were teamed with other products—separate daily and weekly cleaners and saline rinses—to provide a successful regimen for these early soft contact lenses. Early lenses were expected to last an average of about a year between replacements.
Initial studies showed that dual disinfection based on the biguanide (chlorhexidine) and the organomercurial (thimerosal) were effective, non-toxic and safe for use with the lenses of the late 1970s.² As manufacturers began using different chemical approaches in 1984, the new lenses were categorized into four different groups or types.³ Simultaneously, there was an increase in the number of patients choosing cold disinfection over dated heat systems.

Chicago faced an Acanthamoeba outbreak in 2007.8

As dual disinfection became more common, complications with the chlorhexidine and thimerosal combination were reported. In fact, even many of my earlier patients were presenting with red eye reactions; a condition that was attributed to a delayed adverse reaction to the mercury contained in thimerosal. Later, my patients complained of irritation caused by chlorhexidine and began rinsing their lenses with saline prior to insertion. Studies showed that certain types of lenses could absorb and release chlorhexidine, which raised concerns for the use of this drug blend.  Even the chlorhexidine-only products (sans thimerosal) on the market were initially replaced by one and two-step hydrogen peroxide systems.

Polymeric Disinfectants
Two disinfecting systems with single polymeric components were introduced in 1986 and 1987. Polyhexamethylene biguanide (PHMB) was introduced at 0.5ppm in ReNu (Bausch + Lomb) as Dymed and polymeric polyquaterium-1 was introduced at 10ppm in Opti-Free (Alcon) as Polyquad. Initially, both systems used separate cleaners and enzymes to provide an effective regimen for lenses and lens use following prescribed replacements. Each of these approaches met the requirements of the disinfection standards and worked to minimize the risk of allergies or toxic reactions.

All-in-One Disinfectants
Over time, patients’ desire for simple, convenient systems led to the introduction of all-in-one products designed to clean, disinfect, rinse and store contact lenses. These new products were single disinfectant systems based on PHMB or polymeric polyquaterium-1; as the product design evolved, the level of the active ingredient doubled (from 0.5ppm to 1ppm) to achieve an acceptable level of disinfection efficacy. The next step was to enhance the disinfecting efficacy of these all-in-one products without increasing the toxicity. Researchers and scientists knew that the existing formula needed to be supplemented with another active ingredient.

During the mid-to-late 1980s, we saw a spike in two separate infections: one related to long-term extended wear and a second associated with an Acanthamoeba outbreak. The extended wear modality was found to increase the incidence of corneal infection approximately five-fold; as a result, a six night continuous overnight wear limit was implemented. The Acanthamoeba keratitis outbreak was linked to direct contact between tap or chlorine water and the lenses. We soon learned that the polymeric disinfectants were not as effective in combating fungal keratitis as their dual disinfection system predecessors. This was especially true for infections caused by the yeast, Candida albicans, and the mold, Aspergillis fumigates. Standard testing has since replaced Asperigillus fumigatus for Fusarium solani.

Multipurpose Disinfectants Over the Years
The design of the new dual disinfection system emphasized efficacy and biocompatibility. Augmenting the base polymeric polyquaterium-1 formula, 5ppm of the biocide Aldox (myristamidopropyl dimethylamine, Alcon) was added to Opti-Free’s Polyquad to create Opti-Free Express. Today, a multi-purpose disinfecting solution designation indicates that the product is capable of meeting the standalone requirements of the current ISO standard, which include three bacteria (Psuedomonas aeruginosa, Staphylococcus aureus and Serratia marcescans) and two fungi (Candida albicans and Fusarium solani).

Shortly after the development and introduction of the polymeric polyquaterium-1 and biocide biocompatible dual disinfection system, the world of contact lens materials changed dramatically. PureVision (Bausch + Lomb) and Focus Night and Day (CIBA Vision) were the first silicone hydrogel contact lenses. Originally assigned to conventional lens groups, it became quickly apparent that these new lens polymers were different from any soft lens material previously used. PureVision lenses were tested with ReNu Multi-Plus (Bausch + Lomb)—which used 1ppm of PHMB—and Opti-Free Express. The PureVision and PHMB pairing lead to several clinically significant corneal staining cases, while the biocompatible dual disinfection system showed minimal staining.⁴

Gary Andrasko, O.D., carried out an extensive comparison of the staining profiles of solutions and available lens materials.⁵ He found that second-generation multipurpose disinfection solutions, based on the biocompatible dual disinfecting system, were specifically designed with silicone hydrogel materials in mind and include the ingredients in TearGlyde (Alcon) to enhance comfort.

The introduction of silicone hydrogels inspired the development of a single disinfection system. Bausch + Lomb engineered a new low molecular weight biguanide, alexidine, to be added to ReNu with MoistureLoc. Under standard testing conditions, the product showed excellent biocidal activity; however, in 2005-2006, alexidine was implicated in a Fusarium keratitis outbreak and was withdrawn from the market.⁶

In 2007, Chicago faced an outbreak of the Acanthamoeba infection.8 The CDC conducted a detailed investigation, which implicated Complete Moisture Plus (AMO), a product that contained 1ppm of PHMB as the disinfecting agent.⁷ It was subsequently voluntarily recalled. Studies on this product indicated that the formulation ingredients served as a catalyst, causing Acanthamoeba to evolve from a motile feeding to a cyst form designed to protect itself from adverse environments, such as the disinfection process.⁷

Recently, two new products have  been introduced into the U.S. market. Each of these products, Bio-Tru (Bausch + Lomb) and RevitaLens OcuTec (Abbott Medical Optics) is based on a different dual disinfection system. Bio-Tru uses a combination of 1.3ppm of PHMB (30% more PHMB than any previous soft lens disinfecting product) and 1ppm of  polyquaterium-1. RevitaLens OcuTec—FDA approved in September 2010—uses a combination of 1.6ppm of alexidine and 3ppm of polyquaterium-1. Initial testing by Bausch + Lomb shows good disinfecting activity.

A Word of Caution
Ongoing research and development continues to achieve higher levels of safety and disinfecting ability, while keeping patient convenience and comfort in mind. The contact lens solutions used by patients are an essential ingredient in the formula for lens wear success. As eye care practitioners, we must carefully analyze the data available to us to find an ideal solution/lens combination for each patient. Factors, such as lens wearing schedules, patient hygiene habits and lens materials all play a role in determining which solution is the best fit.

Many patients do not understand that earlier generations of solutions—often sold as generics in retail mass merchandising facilities—can be inappropriate for specific types and modalities of lenses. This is why all patients need to be constantly reminded that the solutions prescribed are significant and price should not be an incentive to purchase alternative solutions. As doctors entrusted with the visual health and well being of our patients, it behooves us to monitor solution use with each patient’s follow-up visits. Accurate and updated patient health records can help identify new problems, particularly when linked to a solution change. When all factors are carefully considered, the risk of contamination is significantly reduced, and patients can enjoy wearing lenses without having to worry about developing an infection. 

Dr. Smick is the chief of primary care services at the Clayton Eye Center in Atlanta, Ga. He is also the past president of the Georgia Optometric Association, the Georgia State Board of Examiners in Optometry and the Southern Council of Optometrists. Dr. Smick is a frequent lecturer both in the U.S. and abroad, and currently serves as the chairman of the continuing education committee for the American Optometric Association and the International Vision Expo meetings.

Dr. Smick has no financial interest in any of the products mentioned and is a member of the AMO advisory board.

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2. Bennett E, Weissman B. Clinical Contact Lens Practice. 1st ed. Lippincott, Williams and Wilkins;2005:423.
3. Stone R. Why Contact Lens Groups. Contact Lens Spectrum. 1998 Dec:38-41.
4. Jones L, MacDougall N, Sorbara LG. Assymtomatic corneal staining associated with the use of Balafilcon silicone-hydrogel contact lenses disinfected with a polyaminopropyl biguanide preserved care regimen. Optom Vis Sci. 2002 Dec;79(12):753-61.
5. Andrasko G, Ryen K. Evaluations of MPS and Silicone Hydrogel Combinations. Review of Cornea and Contact Lenses. 2007 Mar:36-42.
6. Levy B, Heiler D, Norton S. Report on testing from an investigation of Fusarium keratitis in contact lens wearers. Eye and Contact Lens. 2007 Dec;32(6):256-61. 
7. Kilvington S, Heaselgrave W, Lally J, et al. Encystment of Acanthamoeba during incubation in multipurpose contact lens disinfectant solutions and experimental formulations. Eye Contact Lens. 2008 May;34(3):133-9.
8. CDC. Acanthameoba keratitis case information. 2010 Nov. Available at: www.cdc.gov/parasites/acanthamoeba/outbreaks/2007/outbreak_cases_ak.html. (Accessed November 2010).