Measurement of Preservative Binding with SOFLENS® (polymacon) Contact Lens*

Abstract

A study was initiated to determine which preservatives, frequently used in ophthalmic solutions, bind with SOFLENS® (polymacon) Contact Lenses. Zone of inhibition assays were employed to detect and measure preservative binding. Lenses soaked in preservative solutions at concentrations normally used in ophthalmic preparations were subjected to various extraction techniques. These lenses were then placed on seeded agar plates of Staphylococcus aureus or Trichophyton mentagrophytes, incubated and examined for the appearance of zones of inhibition. The amount of extraction required to prevent zone formation was interpreted as a measure of preservative binding. Results showed that: (1) thimerosal, thimerosal with disodium edetate, and propylparaben bind weakly; (2) phenyl‐mercuric acetate and phenylmercuric nitrate bind moderately; and (3) chlorhexidine gluco‐nate, benzalkonium chloride, and an alkyl triethanol ammonium chloride compound bind strongly to the lens material.Other studies included in this paper suggested that formulation components and the methods employed for the preparation of commercially available soft contact lens solutions may alter the binding characteristics of the preservative components.