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.
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 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.
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.