The Health Nut Blog

Contact Lenses - Material and Types

What your contact lenses are made of affects how they wear in many senses of the word, including how long they last, your comfort and their health impact. For many years contact lenses were made of glass. Today, fewer than 1% are, with the other 99% made from various types of plastic. The choices are predominantly some type of PMMA (polymethyl methacrylate), polycarbonate or silicon hydroxy gel.

Hard contact lenses introduced in the 1960s are made of PMMA and don't allow oxygen to move directly through the lens, but some air does reach under it anyway. When a person blinks the lens moves slightly and some air diffuses through the tear solution that covers the eyeball.

Soft contact lenses, first introduced in 1971, were made of a polyacrylamide containing nitrogen (hydroxyethyl methacrylate or HEMA) which made them what is called 'hydrophilic'. This ability to absorb water makes them flexible, and therefore more comfortable. At the same time, they are slightly more permeable to air than their older cousins.

RGP (Rigid Gas Permeable) lenses are midway between a truly hard lens, like glass or PMMA, and a soft lens. They combine PMMA with silicone and fluoropolymers that allow air to get to the eye. That increases your comfort and reduces the odds of health problems due to long-term wear.

Extended wear lenses, which come in anywhere from 2-day to 7-day to even 30-day use models, are made of silicon hydroxy gel. That material allows up to seven times the amount of oxygen to pass through the lens, making it possible to wear them longer than others.

Disposable contact lenses, first introduced in 1987, have now become extremely popular. They can be worn daily for a week or two and removing them every night is an option. Most are designed to be worn continuously then simply thrown away. Made from a combination of a polymer called etafilcon (42%) and water (58%), they're very thin, flexible and have excellent gas permeability.

Disposables are especially popular among sports enthusiasts because of the fact that they fit close to the eye, making them very difficult to dislodge. They're also very comfortable, so they can be easily ignored during activity. However, many don't offer quite the level of crystal clear vision as other types, so they're not suitable for everyone. Also, they don't correct some vision problems as well as other types, which limits their use for some.

Apart from the choice of material and wear characteristics, there are several options today in contact lenses that simply didn't exist 20 years ago.

Single vision lenses are like a pair of glasses worn close to the eye. They were once the only choice. Today, bifocals in contact lenses are possible. Even multifocal or progressive lenses are an option. These help compensate for presbyopia, a type of farsightedness that affects nearly everyone as they age, typically beginning in the mid-40s.

Investigate your options with your eye care professional and you'll soon find a pair of contact lenses just right for you and your lifestyle.

# posted by NeilG @ 2:06 AM