The Advantages Of Hard Contact Lenses
The notion of putting a corrective lens on the eye to achieve better vision is certainly nothing new. In fact, Leonardo da Vinci came up with this brilliant idea some 450 years ago. (Although no lenses were manufactured at that time, detailed drawings and descriptions were made.) A. E. Fick, a scientist in Zurich, manufactured the first contact lens in 1887 but soon found out that the human eye didn't like wearing lenses made of actual glass. It took a major innovation, in the 1940s, to produce the ancestors of the contact lenses we wear today: plastics. Those original lenses were made of a material called PMMA, which in fact was so well tolerated by the human eye that it's still used for hard contact lenses, for intraocular lens implants, and for orthopedic purposes.
Soft contact lenses didn't become available in this country until 1972, when Bausch and Lomb first introduced them to the American market. The original soft lenses tended to be more comfortable than the hard lenses available at the time, but because they were limited to just a few sizes, these lenses didn't fit many people. The big difference between hard and soft contact lenses was that the new soft lenses allowed oxygen to pass through them - not just around the lens, as with hard contacts. This made for a much healthier lens environment, because it enabled the eye to "breathe" with a lens in place. Lack of oxygen to the cornea can lead to decreased vision from corneal swelling and epithelial cell damage. Since 1972, contact lenses have changed and improved considerably. Now, lenses are designed to correct almost any vision problem and are available in special designs for extended wear, cosmetic changes (like eye color), and disposability.
Contact lenses come in an impressive variety of materials, sizes, shapes, thicknesses, and colors. In general, they're divided into two major categories: hard and soft. Hard contacts have evolved significantly since their introduction in the 1940s. Initially their design improved as manufacturing techniques improved, but in the late 1970s came a major breakthrough: the development of hard contacts that "breathed" like soft lenses. We call these lenses rigid gas-permeable contacts, or RGPs.
The RGP lenses are more flexible and fit better than earlier hard lenses, and they last longer (with respect to "wear and tear") and sometimes provide better vision than soft lenses. They're manufactured by computer-controlled lathes that can create any kind of surface needed to correct someone's vision. For example, if you have a high degree of astigmatism, an RGP lens can be ground with a curvature to match your cornea perfectly - providing a healthier, more comfortable fit, and vision that's usually superior to that offered by your glasses.
Another significant advantage to RGP lenses is that they can provide in effect, a new cornea for people with a corneal problem that distorts vision. Because this lens maintains its shape on the eye - as opposed to molding itself to the eye, the way a soft lens does - it masks a corneal irregularity, helps correct the optical surface, and improves vision.