|
Gas Permeable (GP) Contact
Lenses:
There is another category of
contact lens materials: gas
permeable (GP) contact
lenses, also known as RGPs,
rigid gas permeable, or
oxygen permeable lenses.
GP contact lenses are rigid,
but they shouldn't be
confused with old-style
"hard" contact lenses, which
are now obsolete. Hard
contact lenses were made of
a material known asPMMA. The
problem with PMMA lenses is
that they are difficult to
get used to and somewhat
uncomfortable to wear. Also,
PMMA does not allow oxygen
to pass through it, and
healthy eyes need plenty of
oxygen.One big difference
between soft lenses and GP
lenses is their size: GP
lenses have a smaller
diameter.
Most GPs incorporate silicon
which makes them more
flexible than PMMA. And
silicone is oxygen
permeable, so oxygen can
pass through GP lenses,
resulting in greater comfort
and better eye health. In
fact, GPs transmit more
oxygen to the eye than do
traditional soft contact
lenses (although some newer
silicon hydrgel soft lenses
are comparable to GPs in
oxygen transmission).
GPs can
also provide better vision,
durability, and deposit
resistance than soft contact
lenses. They can be easier
to clean, and since they're
long-lasting, they can be
less expensive in the long
term than soft lenses.
|
