Rigid Lens Care Systems

Introduction

This chapter reviews the care systems used with rigid contact lenses. Of course, many of the general principles of contact lens care, such as the rationale for lens cleaning and disinfection, regulatory control of the contact lens care industry and various approaches to comparing the efficacy of different solutions, have already been discussed in Chapter 10 and will not be repeated here.

Disinfection and Wetting Solutions

Traditionally, rigid lens products were preserved with benzalkonium chloride, thiomersal and chlorhexidine. However, there is some evidence that sufficient levels of chlorhexidine or benzalkonium chloride can bind to the surface of a rigid lens, leading to a toxic reaction at the ocular surface after lens insertion ( ). More recent products have seen a move away from these preservative agents or, as in the case of the Boston Advance product, a reduction in chlorhexidine concentration compared with previous care solutions. Also, polyhexanide (more traditionally part of soft lens disinfectant products) has been introduced as a second preservative in rigid lens solutions ( Table 18.1 ). For example, Boston Simplus multiaction solution (Bausch & Lomb) contains polyhexanide as its disinfectant ( Fig. 17.1 ).

Multipurpose solutions for cleaning and disinfecting rigid gas-permeable lenses have replaced single-purpose solutions, but there are few reports of the efficacy of these multipurpose solutions, or of the effects of storage conditions on their disinfecting capacities. showed that multipurpose solutions for rigid lenses lose activity over the 3 months’ recommended time of use but remain satisfactory for use. Disinfecting capacity was reduced more quickly when the solution was stored in the refrigerator. Rigid lens disinfecting solutions are not able to kill Acanthamoeba species during manufacturer-recommended disinfection times ( ).

In addition to their role in lens disinfection, most rigid lens storage solutions also act to wet or to condition the lens. This role is principally to act as a lubricant, affording a degree of protection to the cornea and lid margins when the lens is inserted. The cushioning effect minimizes discomfort at insertion. The secondary effects of successful lens wetting are that the lens surface is, first, rendered hydrophilic to aid a stable prelens tear film and, second, made more biocompatible, which might reduce protein deposition.

Various agents are incorporated into rigid lens solutions to aid surface conditioning. Polyvinyl alcohol is a positively charged polymer that is attracted to the negatively charged surface of lenses containing methacrylic acid to provide a more wettable lens ( ). Another agent used to increase wettability is the viscosity agent hydroxyethylcellulose. In addition to preservative and conditioning/wetting agents, rigid lens care solutions contain buffering agents to maintain a stable pH, and chelating agents to increase antimicrobial action and assist in lens cleaning.