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RGPs
Rigid Gas Permeable (RGP) contact lenses are made of plastic
materials that allow oxygen and carbon dioxide to pass through
the lenses. RGP contact lenses are rigid, yet flexible.
Most RGP contact lenses are designed to be worn daily; however,
there are RGP lenses developed for extended wear.
While their popularity has softened in the United States
over the past several years, these lenses are great for
motivated patients who require sharp, clear vision for all
types of situations. In some clinical situations, GP lenses
actually represent a superior choice over soft lenses.
Types of Materials
Rigid gas permeable materials can be divided into two categories:
silicone/acrylate and fluoro-silicone/acrylate. S/A materials
were introduced in 1979 and tended to become less wettable
and stable as the permeability increased, and usage reduced
greatly over the past 10-15 years. F-S/A materials have
been the standard of care since the late 1980s. The addition
of fluorine, wetting agents, and stabilizing agents resulted
in better retention and improved wettability.
RGP lens materials can be divided into three oxygen permeability
(Dk) categories. Low Dk (i.e., 25 - 50) materials are optimum
for myopic daily wear due to their thin designs and good
stability and wettability, and are excellent for bi-toric
designs in minus powers. High Dk (i.e., 51 - 100) materials
are optimum for hyperopic patients, flexible wear patients,
myopic extended wear, and designs with prism ballasted bifocal
segments. Hyper Dk (i.e. > 100) materials are indicated
for RGP extended wear. Some eye doctors prescribe them on
a daily wear basis, but due to their higher softness and
flexibility, are often prescribed on a 6-12 month planned
replacement regimen.
Niche Uses
Myopia Control
Spherical GP lenses offer superior vision since they optically
resurface the ocular surface. In addition, numerous eye
doctors feel wearing GP lenses reduces myopic progression.
Many studies have clearly documented that the application
of GP lenses helps retard the development of myopia by 50%
in children.
Astigmatism
Astigmatism represents another area where GP lenses have
an advantage over soft lenses. Again, by optically resurfacing
the corneal curvature, large amounts of astigmatism can
be corrected.
Keratoconus
Irregular astigmatism represents one of the most problematic
situations a practitioner must manage. Keratoconus, an extreme
case of corneal irregularity, presents a very perplexing
fitting situation because of its extreme corneal asymmetry,
steep corneal curvatures, and irregular astigmatism. This
condition reduces a patient's vision with increasing amounts
of irregular corneal optics, corneal thinning, and corneal
scarring. This is one area where GP lenses have a significant
advantage over soft contacts.
Post-operative refractive surgery
Refractive surgery complications represent another area
where GP lenses do extremely well. These eyes have an abnormal
oblate corneal geometry resulting in flatter central curvatures
and steeper peripheral curvatures.
Orthokeratology/Corneal Refractive Therapy (CRT)
While traditional PMMA and GP lenses have been used for
many years to mold the corneal shape and reduce myopia,
advances in reverse geometry lens designs have enabled eye
doctors to accomplish this therapeutic effect in just one
or two pair of lenses.
Speak with your eye doctor to determine if RGPs are the
right vision correction option for you.
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