Contact
lenses are composed of many chemicals like those found in chemistry
laboratories. They can be grouped into three:
lenses are composed of many chemicals like those found in chemistry
laboratories. They can be grouped into three:
·
Soft conventional contact lens.
Soft conventional contact lens.
·
Hydrogel contact lens and
Hydrogel contact lens and
·
Silicon hydrogel or rigid gas permeable contact lens.
Silicon hydrogel or rigid gas permeable contact lens.
According
to Contact Lens Spectrum, all contact lenses utilizes a polymer backbone.
Silicon hydrogel contact lenses can be worn overnight in some cases. In silicon
hydrogel contact lenses, silicon rubber is used as a polymer backbone.
to Contact Lens Spectrum, all contact lenses utilizes a polymer backbone.
Silicon hydrogel contact lenses can be worn overnight in some cases. In silicon
hydrogel contact lenses, silicon rubber is used as a polymer backbone.
Rigid
gas permeable contact lenses contain different amount of methyl methacrylate,
fluorine, silicon and other chemicals to make them comfortable to wear.
gas permeable contact lenses contain different amount of methyl methacrylate,
fluorine, silicon and other chemicals to make them comfortable to wear.
While
soft conventional hydrogel contact lenses shares a common backbone of the
polymer polyHEMA.
soft conventional hydrogel contact lenses shares a common backbone of the
polymer polyHEMA.
polyHEMA
(poly-2-hydroxyethyl methacrylate) a soft, flexible water-absorbing plastic
used to make soft contact lenses. This polyHEMA is a clear liquid compound
obtained by reacting methacrylic acid (CH2 = C[CH3] CO2H).
(poly-2-hydroxyethyl methacrylate) a soft, flexible water-absorbing plastic
used to make soft contact lenses. This polyHEMA is a clear liquid compound
obtained by reacting methacrylic acid (CH2 = C[CH3] CO2H).
The HEMA
repeating units of the polymer have the following chemical structure.
repeating units of the polymer have the following chemical structure.
In
most cases the polyHEMA chains are cross-linked into a complex three
dimensional network by another compound with which they are copolymerized.
most cases the polyHEMA chains are cross-linked into a complex three
dimensional network by another compound with which they are copolymerized.
Contact
lenses made of polyHEMA were first used in Europe far back 1960s. Their use
surpassed that of hard contact lenses within two years. Since 1980 other
hygroscopic (water absorbing) plaster have been developed, either based on HEMA
or incorporating other flexible polymers such as silicon or HEMA.
lenses made of polyHEMA were first used in Europe far back 1960s. Their use
surpassed that of hard contact lenses within two years. Since 1980 other
hygroscopic (water absorbing) plaster have been developed, either based on HEMA
or incorporating other flexible polymers such as silicon or HEMA.
