• Source: List of soft contact lens materials

Soft contact lenses are one of several types of contact lenses for corrective vision eyewear as prescribed by optometrists and ophthalmologists.




Background



In the US market, soft contact lenses are approved by the US Food and Drug Administration. The American Optometric Association published a contact lens comparison chart called Advantages and Disadvantages of Various Types of Contact Lenses on the differences between them. These include:

soft contact lenses
rigid gas-permeable (RGP)
daily wear
extended wear
disposable
planned replacement contact lenses.
The US Food and Drug Administration (FDA) defines soft contact lenses as:

made of soft, flexible plastics that allow oxygen to pass through to the cornea. Soft contact lenses may be easier to adjust to and are more comfortable than rigid gas permeable lenses. Newer soft lens materials include silicone-hydrogels to provide more oxygen to your eye while you wear your lenses.




= History

=
The first contact lenses were made of glass, in 1888. Initially the glass was blown but soon lenses were made by being ground to shape. For the first fifty years, glass was the only material used. The lenses were thin, yet reports of injury were rare. 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. Lenses made of polyacrylamide were introduced in 1971.




Types


The FDA classifies soft contact lenses into four groups for the US market. They are also subcategorized into 1st generation, 2nd generation, and 3rd generation lens materials. These 'water-loving' soft contact lens materials are categorized as "Conventional Hydrophilic Material Groups ("-filcon"):

Note: Being ionic in pH = 6.0 - 8.0".
The FDA has been considering updating soft contact lens group types and related guidance literature.




Contact lens polymers


The materials that are classified in the 5 FDA groups include the ones listed in the next 5 sections:




= Hydrogel groups

=
Below is a list of most contact lens materials on the market, their water percentage, their oxygen permeability rating, and manufacturer brands. Note that the higher the oxygen transmissibility rating, the more oxygen gets to the eye.



Low water nonionic




High water nonionic




Low Water ionic




High Water ionic




Silicone hydrogel polymers





= Production generations

=
There are three generations of silicone hydrogel contact lens materials:




References

Kata Kunci Pencarian:

• List of soft contact lens materials
• Contact lens
• Google Contact Lens
• Corrective lens
• Polyvinylpyrrolidone
• Fairness to Contact Lens Consumers Act
• Polydimethylsiloxane
• Otto Wichterle
• Contact mechanics
• Presbyopia