Contact Lenses

Types of Contact Lenses

Originally, all contact lenses were made of a hard plastic called polymethyl methacrylate (PMMA). This is the same plastic used to make Plexiglas. But hard lenses don't absorb water, which is needed to help oxygen pass through the lens and into the cornea. Because the eye needs oxygen to stay healthy, hard lenses can cause the wearer a lot of irritation and discomfort. The upside to these lenses is that they are relatively easy to clean because bacteria don't stick very well to them.

Soft contact lenses are more pliable and easier to wear than hard lenses because they're made of a soft, gel-like plastic. Soft lenses are hydrophilic, or "water loving," and absorb water. This allows oxygen to flow to the eye and makes the lens flexible and more comfortable to wear. Many companies bill their soft contact lenses as "breathable" because they transmit a high amount of oxygen to the eye. Letting more oxygen reach the eye means that you can wear soft contact lenses for longer periods with less chance of irritation.

Photo courtesy HowStuffWorks Shopper
Colored contact lenses

Photo courtesy HowStuffWorks Shopper
"Cat eye" cosmetic
contact lenses

Several different types of soft contact lenses are available:
  • Daily-wear lenses - You remove these each night before going to bed.
  • Extended-wear lenses - You can wear these for several days or weeks without removing them.
  • Disposable lenses - You can wear these lenses for a day, a week, or even several weeks before throwing them away.
  • Color-tinted or cosmetic lenses - These lenses change the color of your eyes or tint them for clearer vision outdoors. Other cosmetic lenses drastically change the eye's appearance. Many people use them for the theater or for Halloween.
  • Ultraviolet (UV) protection lenses - These lenses protect against harmful ultraviolet rays from the sun.
  • Corneal reshaping lenses - You wear these lenses overnight and they gradually reshape the cornea to correct your vision. When you take them out, you can temporarily see clearly without contact lenses.

Rigid, gas-permeable lenses, which were developed in the late 1970s, are made from a combination of PMMA, silicone, and fluoropolymers (a type of porous plastic). These lenses combine some of the features of hard and soft contact lenses. They're more durable than soft lenses, but they still allow oxygen to pass into the eye, making them more comfortable to wear than hard lenses. Because they don't contain water, they are less likely to develop bacteria and cause infection than soft lenses. The rigidity of the lens provides clear, crisp vision.

Super Lenses for Superstar Athletes
Athletes need special gear to perform at their best, and their vision is no exception. Without his custom-designed contact lenses, Mark McGwire wouldn't have been able to see a baseball coming over the plate, let alone break Roger Maris' home run record. McGwire's eyesight is 20/500, but with contacts he has 20/10 vision. Mark McGwire's contact lenses are special: they don't just correct his vision, they make it sharper and crisper than normal.

New sport-tinted contact lenses filter out certain wavelengths of light to sharpen visual details for athletes. They also reduce sun glare and protect athlete's eyes from harmful UV rays. The lenses come in amber and gray-green. Amber works best for fast-moving sports such as baseball and soccer. It blocks out annoying blue light and accentuates the reds. Gray-green is best for slow-moving sports, such as golf, that are played in the bright sunlight. Currently only professional athletes can get these lenses, but they should be available to the public by the summer of 2006 and should cost about the same as regular contact lenses.