Soft lenses, which are more widely used because of their almost immediate comfort and extensive promotion by soft lens manufacturers, are available in several options. They were originally worn for approximately two years before replacement. However, a limitation of soft lens materials is that they accumulate protein and other irritating substances, which can lead to discomfort and reduced wearing time. Attempts to remove these substances have largely been ineffective. Frequent replacement of soft lenses on a monthly, weekly or daily basis is now feasible and cost effective, eliminating this problem.
While the initial adaption period for rigid gas permeable (RGP) contact lenses is longer, there are some definite advantages with an effective lens life of between two and five years. In addition, astigmatism (a common focusing error) is more easily corrected with this type of lens. Dehydration can present problems with soft lenses, especially in airconditioned environments, but is less of a problem with RGP lenses. This type of lens cannot be used by everyone, but patients who are suitable candidates are often the most successful contact lens wearers, rarely reverting their spectacles.