public wearing contact lenses, under the supervision of Dr. Alan Isen, who developed the first commercially viable soft-contact lenses in the United States. Early corneal lenses of the 1950s and 1960s were relatively expensive and fragile, resulting in the development of a market for contact lens insurance. Replacement Lens Insurance, Inc. (now known as RLI Corp.) phased out its original flagship product in 1994 after contact lenses became more affordable and easier to replace. Gas permeable and soft lenses (1959-current) One major disadvantage 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-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. Collectively, these polymers are referred to as 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 to 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. 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. 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. The Czech scientists' work led to the launch of the first soft (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