How to use hard lenses in a sentence? Find typical usage patterns (collocations)/phrases/context for "hard lenses" and check conjugation/comparative form for "hard lenses". Mastering all the usages of "hard lenses" from sentence examples published by news publications.
In 1938 perspex (polymethylmethacrylate, or PMMA) began to replace glass in contact lens manufacture. PMMA lenses were easier to produce so the production of glass lenses soon ended. Lenses made of PMMA are called hard lenses. Soft contact lenses were first produced in 1961 by Czech chemical engineer Otto Wichterle using polyhydroxyethylmethacrylate (pHEMA), a material that achieved long-term commercial application.
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Glass lenses were never comfortable enough to gain widespread popularity. The first lenses to do so were those made from polymethyl methacrylate (PMMA or Perspex/Plexiglas), now commonly referred to as "hard" lenses. Their main disadvantage is they do not allow oxygen to pass through to the cornea, which can cause a number of adverse, and often serious, clinical events. Starting in the late 1970s, improved rigid materials which were oxygen-permeable were developed.
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Once on the contact lens, Acanthamoeba is able to survive in the space between the contact lens and the surface of the eye. Soft contact lenses are more adherent to the corneal surface than hard lenses, which allows the Acanthamoeba organism to bind to mannosylated glycoproteins on the corneal surface. Expression of these proteins on the corneal surface is increased by contact lens use. This increase in glycoprotein content, along with microtrauma to the corneal epithelial surface due to contact lens use increases the risk for infection.
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Floating like a fishing line bob, the lamp is positioned underwater by weights on its submerged power supply cord. The bulb is fragile so some manufacturers offer protective covers and hard lenses. However, one unique feature of a submerged, unprotected bulb is that its outer glass envelope gets hot enough during operation to prevent establishment of marine growth on its surface. If the bulb has a protective cover or is not operated every night for at least an hour, occasional manual cleaning is required.
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Rigid gas-permeable (RGP) lens A rigid gas-permeable lens, also known as RGP lens or GP lens or colloquially, hard contact lens, is a rigid contact lens made of oxygen-permeable polymers. Initially developed in the late 1970s, and through the 1980s and 1990s, they were an improvement over prior 'hard' lenses that restricted oxygen transmission to the eye. Rigid lenses are able to replace the natural shape of the cornea with a new refracting surface. This means that a regular (spherical) rigid contact lens can provide good level of vision in people who have astigmatism or distorted corneal shapes as with keratoconus.
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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. 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.
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