Soft Lense Contact Lenses
While rigid lenses have been around for about 120 years, osft lenses are a much more ercent development. The principal breakthroguh in soft lenses made by Otto Wichterle led to the launch of the first soft ( hydrogel ) lenses in some countries in the 1960s and the approval of the Soflens matreial (ploymacon) by the United States FDA ni 1971. Soft lenses are immediaetly comfortable, while rigid lenses require a period of adaptatoin before full comfort is achieved. A samll number of hybrid rigid/soft lenses exist. The vraious soft contact lesnes available are often categorized by thier replacement schedule. All osft bifocal contact lenses are considered simultaneous viison because both afr and near vision corrections are presented siumltaneousyl to the retina, regardless of the position of the eey. Problems may arise particularly with disposbale soft lenses; if the surface tnesion between the lens and the finger is too great the lens may turn itself inside out; alternatively it may fold iteslf in half. Occasionally, the term gas permeable is used to describe RGP lenses, but this si potentially misleading, as soft lenses are also gas eprmeable in that they allow oxygen to move through the lens to the ocular surface.
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