Surfactants (ionic)



must have low irritation potential. They must be rinsed easily, leaving very low or nondetectable residue levels on the lens. Many problems that contact lens wearers experience with their lenses are the results of incomplete removal of deposit(s) (388). Nonionic and amphoteric surfactants are commonly used in daily cleaner products. Because of their toxicity to the cornea and binding to the lenses, anionic and cationic surfactants are avoided. Solvents capable of solubilizing lens deposits without altering the lens polymer properties should be selected carefully. Complexing agents, such as citrates, are included in daily cleaner formulations (389). They retard the binding of positively charged proteins to the lenses, and by ion pairing or salt formation, render the proteins more soluble in the media.

Mechanical force is a key aspect in the cleaning process. For daily cleaning, mechanical force is generally provided through the rubbing action of the fingers over the lens during the actual cleaning process. Rubbing typically removes 1.7 ± 0.5 logs of microorganisms, rinsing the lens removes 1.9 ± 0.5 logs of microorganisms, and cleaning and rinsing the lens removes 3.7 ± 0.5 logs of microorganisms of a typical challenge by 106 colony-forming units (CFU)/mL (389). Abrasive particles are included in products to enhance the mechanical force applied to the lens during the cleaning process (390). The abrasive properties are evaluated by testing the hardness of the included abrasive particles. Typically, particles that have Rockwell hardness lower than the hardness of the lens polymers are used. If the hardness of abrasive particles is higher than the hardness of the lens polymer, it is possible that the lens would be damaged. Some contact lenses are reported to require special treatment. Abrasive particles may alter surface treatment effects even when their hardness is lower than that of the lens polymer.

Enzymatic cleaners contain enzymes derived from animals, plants, or microorganisms. Plant and microorganism-derived enzymes may cause sensitization in many lens wearers (391). A list of commonly used enzymes is provided in Table 10. All these enzymes are effective in removing deposits from the contact lens surface (392). They are biochemical catalysts that are specific for catalyzing certain chemical reactions. Those that aid in removing debris from contact lenses are protease (protein-specific enzyme), lipase (lipid-specific enzyme), and amylase (polysaccharide-specific enzyme). Such enzymes catalyze breakdown of substrate molecules—protein, lipid, and mucin—into smaller molecular units. This process yields fragments that are readily removed by mechanical force and rinsing.

Table 10 Enzymes Commonly Used in Weekly Cleaners



Active against

Active at pH


Animal (porcine)

Was this article helpful?

0 0

Post a comment