Differentiation
Perhaps the most useful method for diffentiation between types of lens is by using their functional design. Soft lenses may be daily disposable, extended wear or reusable, monthly lenses may be extended wear or reusable the choice of which to have is often largely down to personal preference and other concerns such as expense. Lenses designed for annual or quarterly wear though once popular have now largely been replaced by more convenient disposal regimes.
Contact lenses, as is the case in normal eye glasses may be monofocal, bifocal or multifocal depending on the individual complaint of the wearer. Similarly they may be designed to correct for only spherical aberrations or spherical and cyclindrical aberrations.
Spherical lenses are comprised of combined inner and outer optical surfaces which are both portions of a sphere and correct for simple near or long vision.
Lenses designed to correct astigmatism or Toric lenses are prescribed for patients suffering from astigmatism, in these lenses one or both of the optical surfaces is a cylindrical lens, usually in combination with a spherical lens, the presence of two or more different optical surfaces give rise to a planar refractive entity and as such Toric lenses are usually weighted to allow them to settle into the right orientation once fitted.
Lenses designed to correct presbyopia are often multifocal with the inner portion of the lens being designed to correct myopia and the outer ring similarly designed to correct hypermetropia. These lenses are difficult to fit and expensive to manufacture.
Disclaimer: The author is not a medical doctor, optician, ophthalmologist or any other medical professional, this article has been compiled using a variety of internet reference sources and while every effort has been made to ensure accuracy this cannot be guaranteed. No preference for product or brand is inferred or intended and the contents of this article are not to be used in whole or in part to inform a decision regarding any aspect of contact lens use.
