Editing Contact lens (section)

===Gas permeable and soft lenses (1959–present)===

One of the major disadvantages of PMMA lenses is that they allow no oxygen to get through to the [[conjunctiva]] and cornea, causing a number of adverse and potentially serious clinical effects. By the end of the 1970s and through the 1980s and 1990s, a range of [[Oxygen permeability|oxygen-permeable]] but rigid materials were developed to overcome this problem. Chemist [[Norman Gaylord]] played a prominent role in the development of these new oxygen-permeable contact lenses.<ref name="bc">{{Cite web |last=Pearce, Jeremy |date=23 September 2007 |title=Norman Gaylord, 84; helped develop type of contact lens |url=http://www.boston.com/news/globe/obituaries/articles/2007/09/23/norman_gaylord_84_helped_develop_type_of_contact_lens/ |access-date=6 October 2007 |website=(New York Times News Service) |publisher=[[The Boston Globe]]}}</ref> Collectively, these [[polymers]] are referred to as ''[[RGP lens|rigid gas permeable]]'' or RGP materials or lenses. Though all the above contact lens types—sclerals, PMMAs and RGPs—could be correctly referred to as "rigid" or "hard", the latter term is now used for the original PMMAs, which are still occasionally fitted and worn, whereas "rigid" is a generic term for all these lens types; thus, hard lenses (PMMAs) are a subset of rigid contact lenses. Occasionally, the term "gas permeable" is used to describe RGPs, which is somewhat misleading as soft contact lenses are also gas permeable in that they allow oxygen to get through to the ocular surface.

[[File:Prof. Ing. RTDr. Otto Wichterle.jpg|thumb|upright|[[Otto Wichterle]] (pictured) and [[Drahoslav Lím]] introduced modern soft hydrogel lenses in 1959.]]

The principal breakthrough in soft lenses was made by Czech chemists [[Otto Wichterle]] and [[Drahoslav Lím]], who published their work "Hydrophilic gels for biological use" in the journal ''Nature'' in 1959.<ref name="Wichterle">{{Cite journal |vauthors=Wichterle O, Lim D |year=1960 |title=Hydrophilic gels for biological use |journal=Nature |volume=185 |issue=4706 |pages=117–118 |bibcode=1960Natur.185..117W |doi=10.1038/185117a0 |s2cid=4211987}}</ref> In 1965, [[National Patent Development Corporation]] (NPDC) bought the American rights to produce the lenses and then sublicensed the rights to [[Bausch & Lomb]], which started to manufacture them in the United States.<ref>{{Cite web |title=CONTACT LENS HISTORY – Otto Wichterle |url=http://www.andrewgasson.co.uk/opioneers_wichterle.htm |url-status=dead |archive-url=https://web.archive.org/web/20150129033858/http://www.andrewgasson.co.uk/opioneers_wichterle.htm |archive-date=29 January 2015 |access-date=26 March 2015 |df=dmy-all}}</ref> The Czech scientists' work led to the launch of the first [[hydrogel]] contact lenses in some countries in the 1960s and the first approval of the Soflens material by the US [[Food and Drug Administration]] (FDA) in 1971. These soft lenses were soon prescribed more often than rigid ones, due to the immediate and much greater comfort (rigid lenses require a period of adaptation before full comfort is achieved). Polymers from which soft lenses are manufactured improved over the next 25 years, primarily in terms of increasing oxygen permeability, by varying the ingredients. In 1972, British optometrist Rishi Agarwal was the first to suggest disposable soft contact lenses.<ref>{{Cite journal |last=Agarwal Rishi K |year=1972 |title=Some Thoughts on Soft Lenses |journal=The Contact Lens |volume=4 |issue=1 |page=28}}</ref><ref>{{Cite journal |year=1988 |title=Editorial note |journal=American Journal of Optometry and Physiological Optics |volume=65 |issue=9 |page=744}}</ref>

In 1998, the first silicone hydrogel contact lenses were released by [[Ciba Vision]] in Mexico. These new materials encapsulated the benefits of silicone which has extremely high [[oxygen permeability]]—with the comfort and clinical performance of the conventional hydrogels that had been used for the previous 30 years. These contact lenses were initially advocated primarily for extended (overnight) wear, although more recently, daily (no overnight) wear silicone hydrogels have been launched.

In a slightly modified molecule, a polar group is added without changing the structure of the silicone hydrogel. This is referred to as the Tanaka monomer because it was invented and patented by {{ill|Kyoichi Tanaka|ja|田中恭一}} of {{ill|Menicon|ja|メニコン}} Co. of Japan in 1979. Second-generation silicone hydrogels, such as [[galyfilcon A]] ([[Acuvue]] Advance, Vistakon) and [[senofilcon A]] (Acuvue Oasys, Vistakon), use the Tanaka monomer. Vistakon improved the Tanaka monomer even further and added other molecules, which serve as an internal [[wetting agent]].<ref name="szcz" />

[[Comfilcon A]] (Biofinity, CooperVision) was the first third-generation polymer. Its patent claims that the material uses two siloxy macromers of diverse sizes that, when used in combination, produce very high oxygen permeability for a given water content. [[Enfilcon A]] (Avaira, CooperVision) is another third-generation material that is naturally wet; its water content is 46%.<ref name="szcz" />