Water content in contact lenses
Water content of a lens is expressed by percentage of water volume in a particular material. The optimal amount is about 60%. For hydrogel soft lenses transparency of media is dependent on the water content. Material aging decreases the water content and affects contact lens permeability for light (such a lens has a yellow or gray tint). Such a lens is already unusable. If a soft contact lens dries out, it is damaged and needs to be replaced.