Contact Lens Materials
Up
until the late 1970s, contact lenses were made from two materials.
Hard contact lenses were made of polymethymethacrylate (PMMA),
while the soft contact lenses were made of a hydrated polymer,
hydroxyethylmethacrylate (HEMA), which contained 37.8% water by
weight. These lenses provided clear vision and comfort, but there
was a problem. These lenses did not allow oxygen to reach the
cornea. Because of this, the cornea could change, adversely, in
some contact lens wearers.
PMMA
is now obsolete, and is replaced with rigid plastics, mostly
hydrophobic materials with high oxygen permeability. These lenses
are called Rigid Gas Permeable (RGP) lenses. For the manufacture
of soft lenses, HEMA is being replaced by polymers which contain
as much as 80% water. These soft lenses, often called hydrogels
because of the amount of water have high oxygen transfer while
retaining shape despite high water content. These new materials
used in the manufacture of contact lenses as well as thinner
lenses and greater oxygen transfer has reduced corneal issues, but
there are still other possible complications.
The
new materials have also been instrumental in the creation of
disposable contact
lenses in a variety of types. Disposable contact lenses come in
monthly, bi-monthly, weekly, and even daily disposable types. The
thinner materials make wearing these contact lenses more
comfortable, and the cost of contact lenses has been reduced. This
allows for close to maintenance free contact lens wear.
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