Contact lens wetting and biocompatibility

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For the best patient outcome, a contact lens must be biocompatible with surrounding ocular tissue. This success depends heavily on the interactions of the surface of the contact lens with the tear film and corneal tissues. A highly biocompatible surface has a very low tear-lens surface interfacial tension, therefore creating a highly wettable surface on which tears spread readily (Figure 1). The surfaces of hydrogel and silicone hydrogel contact lenses are composed of polymer chains which are both hydrophilic (water-loving) and hydrophobic (water-repelling). Portions of these chains have the ability to rotate, to shift position around a chemical bond, a process called hydrophilic-hydrophobic transition. Hydrogel surfaces exposed to water will tend to be populated in hydrophilic groups, while those surfaces exposed to air or nonpolar fluid can collect hydrophobic groups.3