Different types of contact lenses
Here are the basics you should know about contact lenses before seeing your eye doctor (you are interested in wearing contacts).
Contact lens materials
The first choice when considering contact lenses is which lens material will best satisfy your needs. There are five types of contact lenses, based on type of lens material they are made of:
Soft lenses are made from gel-like, water-containing plastics called hydrogels. These lenses are very thin and pliable and conform to the front surface of the eye.
Silicone hydrogel lenses are made of an advanced type of soft contact lens material that allows more oxygen to pass through the lens and reach the front surface of the eye. Silicone hydrogel contact lenses are now the most popular type of contact lenses.
Gas permeable lenses. Also called GP or RGP lenses, these are rigid contact lenses that maintain their shape on the eye, enabling them to correct astigmatism and other refractive errors. Gas permeable contact lenses typically are smaller in diameter than soft lenses and are made of highly oxygen-permeable materials. It usually takes some time for your eyes to adjust to GP lenses when you first start wearing them; but after this initial adaptation period, most people find GP lenses are as comfortable as soft lenses.
Hybrid contact lenses have a rigid gas permeable central zone, surrounded by a "skirt" of hydrogel or silicone hydrogel material. They are designed to provide wearing comfort that rivals soft or silicone hydrogel lenses, combined with the crystal-clear optics of GP lenses.
PMMA lenses are rigid contact lenses that look like GP lenses but are made of a plastic material that is not oxygen permeable. PMMA lenses were commonly prescribed years ago, but essentially have been replaced by gas permeable lenses.
Contact lens wearing time
There are two categories of contact lenses based on recommended wearing time:
Daily wear contact lenses — These must be removed nightly before sleep.
Extended wear contact lenses — These can be worn overnight (for a limited number of days).
"Continuous wear" is a term that's sometimes used to describe extended wear lenses that are worn 24 hours per day for up to 30 consecutive days.
When to replace your 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 lenses — Discard after a single day of wear
Disposable lenses — Discard every two weeks, or sooner
Frequent replacement lenses — Discard monthly or quarterly
Traditional (reusable) lenses — Discard every six months or longer
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
Soft contact lenses (both hydrogel and silicone hydrogel lenses) are available in a variety of designs, depending on their intended purpose:
Spherical contact lenses have the same lens power throughout the entire optical part of the lens to correct myopia (nearsightedness) or hyperopia (farsightedness).
Toric soft contact lenses have different powers in different meridians of the lens to correct astigmatism as well as nearsightedness or farsightedness.
Multifocal contact lenses (including bifocal contacts) contain different power zones for near and far vision to correct presbyopia as well as nearsightedness or farsightedness. Some multifocal lenses also can correct astigmatism.
Cosmetic contact lenses include color contacts designed to change or intensify your eye color. Halloween, theatrical and other special-effect contacts also are considered cosmetic lenses. A contact lens prescription is required for cosmetic contacts even if you have no refractive errors that need correction.
All of these lenses can be customized for hard-to-fit eyes. Other lens designs also are available — including lenses fabricated for use in special situations, such as correcting for keratoconus.
More contact lens features
Bifocal contacts for astigmatism. These are advanced soft contacts that correct both presbyopia and astigmatism, so you can remain glasses-free after age 40 even if you have astigmatism.
Contacts for dry eyes. Are your contacts uncomfortably dry? Certain soft contact lenses are specially made to reduce the risk of contact lens-related dry eye symptoms.
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. Other colored lenses can totally change the color of your eyes, as in from brown to blue.
Special-effect lenses. Also called theatrical, novelty, or costume lenses, special-effect contacts take coloration one step further to make you look like a cat, a vampire, or another alter-ego of your choice.
Prosthetic lenses. Colored contact lenses also can be used for more medically oriented purposes. Opaque soft lenses called prosthetic contacts can be custom-designed for an eye that has been disfigured by injury or disease to mask the disfigurement and match the appearance of the other, unaffected eye.
Custom lenses. If conventional contact lenses don't seem to work for you, you might be a candidate for custom contact lenses that are made-to-order for your individual eye shape and visual needs.
UV-inhibiting lenses. Some soft contact lenses help protect your eyes from the sun's ultraviolet rays that can cause cataracts and other eye problems. But because contacts don't cover your entire eye, you still should wear UV-blocking sunglasses outdoors for the best protection from the sun.
Scleral lenses. Large-diameter gas permeable lenses called scleral contacts are specially designed to treat keratoconus and other corneal irregularities, as well as presbyopia. Myopia control contacts. Special contact lenses are being developed to slow or stop the progression of nearsightedness in children.
Which contact lenses are right for you?
There are a number of factors that can influence which contact lenses are best for you:
The contact lenses 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.
The lenses must fit your eyes. To do that, lenses come in tens of thousands of combinations of diameter and curvature. Of course, not every lens brand will have the size you need.
You may have a special need that drives the choice of lens. For example, your eye doctor might recommend a particular type of contact lens if your eyes tend to be dry.
Consider your "wish list" of contact lens features — colors, for example, or overnight wear.
Consult your eye doctor to determine the best contact lens material and design for your specific needs.
Contact lens wear and care
Caring for your contact lenses — cleaning, disinfecting and storing them — is quite simple.
Most people require only a single multipurpose solution to clean, disinfect and safely store their lenses.
People who are sensitive to the preservatives in multipurpose solutions might need preservative-free systems, such as those containing hydrogen peroxide.
Your eye doctor will recommend a lens care system. Be sure to follow the care directions carefully.
Of course, you can avoid lens care altogether by wearing daily disposable contact lenses.
Contact lens problems
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 your eyes or lenses are uncomfortable or you are not seeing well, remove your lenses and consult your eye doctor immediately.
Buying contact lenses
Once you have a valid contact lens prescription, you can buy replacement contact lenses at many places, and some offer a better value than others.
Page published on Friday, 22 March, 2019