Contact Lens Basics

By Liz Segre

Contact lenses, like eyeglasses or LASIK, can correct your nearsightedness, farsightedness and astigmatism. Among Americans who need vision correction, about 20 percent wear contact lenses.

While some people enjoy making a fashion statement with eyeglasses, others prefer their appearance without them. Contact lenses can achieve this without irreversible refractive surgery. Contact lenses can also provide a full field of unobstructed vision, which is great for sports.

Contact lenses have been around for more than a hundred years. During that time, many advancements have allowed just about everyone to wear contact lenses. If you were told in the past that you couldn't wear contact lenses, odds are that's not true today. There are more convenient and healthy contact lens options than ever.

If you're new to contact lenses, your first step is to see an eye doctor. In the United States, contact lenses are a prescription item, just like pharmaceuticals. They must be prescribed and properly fitted by an eye care professional (ECP). Your ECP will evaluate your visual needs, your eye structure, and your tears to help determine the best type of lens for you.

The many types of contact lenses currently available can be grouped in various ways according to:

• What they're made of
• How long you wear them without removal
• How often you dispose of them
• The design of the lens

Contact Lens Materials

Classified by material, there are three types of contact lenses:

• Hard lenses are made from PMMA — also known as Plexiglas or Lucite. These lenses are virtually obsolete and rarely used.
• Soft lenses are made from gel-like, water-containing plastics, and are most common. They're a bit larger in size than your iris.
• GP lenses, also known as RGP or "oxygen permeable" lenses, are made from rigid, waterless plastics and are especially good for presbyopia and high astigmatism. These lenses are usually about eight millimeters in diameter, which is smaller than your iris.

From the introduction of soft lenses in 1971 until several years ago, most lens brands were made from "hydrogel" plastics. Then silicone hydrogel contact lenses were introduced. They have become the contact lenses of choice for many eye care practitioners, because they allow more oxygen to pass through the lens to the eye, and they are less prone to dehydration.

Contact Lens Wearing Time

Until 1979, everyone who wore contact lenses removed and cleaned them nightly. The introduction of "extended wear" enabled wearers to sleep in their contacts. Now, two types of lenses are classified by wearing time:

• Daily wear — must be removed nightly
• Extended wear — can be worn overnight, usually for seven days consecutively without removal

"Continuous wear" is a term that's sometimes used to describe 30 consecutive nights of lens wear — the maximum wearing time approved by the FDA for certain brands of extended wear lenses.

Disposal Intervals for Contact Lenses

Even with proper care, contact lenses (especially soft contacts) should be replaced frequently to prevent the build-up of lens deposits and contamination that increase the risk of eye infections.

Soft lenses have these general classifications, based on how frequently they should be discarded:

• Daily disposable — Discard after a single day of wear
• Disposable (used for daytime wear) — Discard after two weeks
• Disposable (used for overnight wear) — Discard after one week
• Continuous wear (used for 30-day wear) — Discard monthly
• Planned replacement — Discard monthly or less frequently

Gas permeable contact lenses are more resistant to lens deposits and don't need to be discarded as frequently as soft lenses. Often, GP lenses can last a year or longer before they need to be replaced.

Contact Lens Designs

Many lens designs are available to correct various types of vision problems:

• Spherical contact lenses are the typical, rounded design of contact lenses, which can correct myopia (nearsightedness) or hyperopia (farsightedness).
• Bifocal contact lenses contain different zones for near and far vision to correct presbyopia [more about bifocal contacts].
• Orthokeratology lenses are specially designed to reshape the cornea during sleep, providing lens-free daytime wear [more about ortho-k].
• Toric contact lenses correct for astigmatism, as well as for myopia and hyperopia [more about toric contacts].

All of these lenses can be custom made for hard-to-fit eyes. Many other additional lens designs are available. Typically these are less common and fabricated for use in special situations, such as correcting for keratoconus.

More Contact Lens Features

Colored Lenses. Many of the types of lenses described above also come in colors that can enhance the natural color of your eyes — that is, make your green eyes even greener, for example. Or these lenses can totally change the eye's appearance, as in from brown to blue. [More about colored lenses.]

Special-Effect Lenses. Also called theatrical, novelty, or costume lenses, these take coloration one step further to make you look like a cat, a zombie, or another alter-ego of your choice. [More about special-effect contacts.]

Prosthetic Lenses. Colored contact lenses can also be used for more medically oriented purposes. People with disfigured eyes, as a result of accidents or disease, can use a custom, opaque colored lens to mask the disfigurement and match the appearance of their normal eye. [More about prosthetic contacts.]

Custom Lenses. If conventional contact lenses don't seem to work for you, you might be a candidate for a customized design. [More about custom lenses.]

UV-Inhibiting Lenses. Today, many contacts incorporate an ultraviolet blocker in the lens material, to cut down on UV light that can eventually cause cataracts and other eye problems. You can't see this blocker by looking at the lens. And since contacts don't cover your entire eye, UV blockers cannot substitute for traditional sun protection like good quality sunglasses.

Hybrid Lenses. One brand of lenses features a GP center with a soft outer skirt, providing wearers with both the crisp optics of a rigid lens and the comfort of a larger, soft lens.

Which Contact Lens Is Right for You?

First, your contacts must address the problem that is prompting you to wear lenses in the first place. Your contact lenses must provide good vision by correcting your myopia, hyperopia, astigmatism, or some combination of those vision problems.

Second, the lens must fit your eye. To do that, lenses come in tens of thousands of combinations of diameter and curvature. Of course, not every lens brand comes in every "size."

Your ECP is skilled in evaluating your eye's physiology, and your eyesight, to determine which lens best satisfies the two criteria above.

Third, you may have another medical need that drives the choice of lens. For example, your ECP might pick a particular lens if your eyes tend to be dry.

Finally, consider your "wish list" of contact lens features — colors, for example, or overnight wear.

When you and your ECP decide on the right lens for you, you'll be given a contact lens prescription. You'll be able to buy a supply of lenses from your ECP or from the many other outlets that sell contact lenses. [For more on this, please read "Where's the Best Place to Buy Contact Lenses?"]

Contact Lens Wear and Care

Caring for your contact lenses — cleaning, disinfecting and storing them — is much easier than it used to be.

A few years ago, you would have needed several bottles of cleaning products, and perhaps enzyme tablets, for proper care. Today, most people can use "multipurpose" solutions — meaning that one product both cleans and disinfects, and is used for storage. Some people who are sensitive to the preservatives in multipurpose solutions might need preservative-free systems, such as those containing hydrogen peroxide.

Of course, you can avoid lens care altogether by using daily disposables.

Contact Lens Problems

Trial and error often is involved in finding the perfect lens for you. People react differently to various lens materials and cleaning solutions. Also, the correct "parameters" of your lens — that is, power, diameter, and curvature — can be finalized only after you've successfully worn the lens. This is especially true for more complex fits involving extra parameters, such as with bifocals or toric contact lenses for astigmatism.

If you experience discomfort or poor vision when wearing contact lenses, chances are that an adjustment or change of lens can help. Today, more contact lens choices than ever are available to provide comfort, good vision, and healthy eyes. If you're not feeling good and seeing well, ask your ECP for help.

Buying Contact Lenses

There are many places you can buy replacement contact lenses, and some offer a better value than others. Find out more about where to buy contacts and buying contact lenses online.

More Information About Contacts

For more information about contacts, visit our contact lens FAQ, eye doctor Q&A and contact lens news pages.

[Page updated April 2009]