Contact lens wettability is vital to lens wearing comfort. Solutions vary in their ability to adequately wet a lens surface. It is important to be able to measure the wettability of contact lenses that have been soaked in different lens care solutions. Such a measurement can be taken by observing the contact angle of a water drop upon a contact lens surface. When a water drop falls on a surface, the contact angle is a measure of natural forces that cause the drop to either bead up or spread out, depending on the surface wettability.

If a surface is dry (or hydrophobic), the contact angle (and surface tension) is high. The water-repelling surface causes a water drop to bead up. However, if a surface is wet (or hydrophilic), the contact angle is low, and the water drop wants to spread out over the surface.

A good wetting agent should condition a hydrophobic (or non-wettable) surface to be hydrophilic and maintain the hydrophilic surface over the entire lens-wearing day. The lower the contact angle, the better the wetting agent.