Contact lenses are small, plastic disks that float over the cornea or sclera on a natural layer of tears, usually to correct vision problems such as
nearsightedness, farsightedness, astigmatism
and presbyopia. They are also worn after cataract removal and for other eye conditions.
At least 31 million people in the U.S. currently wear contact lenses, which can offer several benefits over eyeglasses. Besides the cosmetic advantages, contacts provide correction for a wider field of vision because they are on the surface of the eye and move with it – rather than in front of it and in a stationary position. They also don't fog up in cold or wet weather and reduce the risk of injury or mishap during physical activities.
Nearly everyone can wear contact lenses because there are so many types available, most of which fall under two basic categories: rigid lenses and soft lenses. There are also several types of specialty lenses, which may be available in both rigid and soft materials.
Rigid Contact Lenses
Rigid lenses include popular Rigid Gas-Permeable (RGP) contacts and the traditional PMMA (polymethyl methacrylate) “hard” lenses, which are now virtually obsolete. Newer rigid lenses are known for their durability, ease of handling and vision clarity.
- RGPs are generally considered to provide the crispest vision and be the healthiest contact lenses for your eyes. Many of today’s RGPs are produced with silicone, making them more flexible than the old PMMA “hard” lenses but allowing more oxygen to “permeate” through the eyes than even soft lenses. Because their material is rigid, they may initially be less comfortable than soft lenses and take longer to get used to – especially for people with sensitive eyes. However, the material rigidity also allows for easier handling, less fragility and a longer lens life.
RGP lenses, which are smaller than soft lenses, usually come with a slight blue tint – not so much as to change eye color or vision, but enough to make them easier to locate. With proper care, which should include cleaning and disinfection each time they are removed (depending on the type), they can last several years.
- Hard lenses made from PMMA are the original contact lenses, but they are rarely prescribed today because they are very problematic. Unlike newer RGPs, PMMA lenses are non-permeable (although some oxygen reaches the cornea through tears, which passes behind the lens), resulting in discomfort and increased risk of eye infections and disease. These lenses are also high-maintenance, require a long adjustment period and can lead to long-term corneal damage. If you still wear hard lenses, you should see an eyecare provider about replacement lenses.
These are the most widely prescribed, known for their comfort, affordability, ease-of-wear and convenience. However, vision with soft contact lenses may not be as sharp as with RGPs. Made from a gel-like plastic, soft lenses have a water content ranging from 36 and 79 percent, depending on the type and brand. (RGPs contain no water.) Generally, the higher the water content, the more oxygen reaches the cornea – good for your eyes but making it harder for you to handle the lens. For most people, a mid-water content material (around 60-65 percent) is recommended because they combine high oxygen transmissibility with ease of handling.
Although extended wear products are available, soft lenses are usually designed for short-term use because bacteria, fungi and other contaminants can be trapped in the porous material, leading to infection and even vision loss. Among the types fo soft lenses:
- Daily Wear soft lenses are made of soft, flexible plastics that allow oxygen to easily pass through to the eyes. They require nightly cleaning and disinfecting and should be replaced at least once a year. These lenses are relatively inexpensive, provide easy adaptability, are more comfortable and are harder to dislodge than RGP lenses. They are available in tints and bifocals and are ideal for active lifestyles.
- Disposable/Planned Replacement soft lenses are similar to the daily-wear soft lenses but as the name suggests, they are discarded and replaced according to a pre-determined wearing schedule – either each night, every 2 weeks, every 4 weeks or every 3 months. While daily disposables are worn for one day and replaced with a new pair the next day, eliminating any need for cleaning solutions, the other disposables still must be cleaned nightly before they are replaced.
Since these lenses are discarded in a shorter time frame, protein deposits that can accumulate over time and cause eye problems are less of an issue than with daily wear lenses, theoretically resulting in a lower risk of eye infections. And you can use a more simplified cleaning and disinfecting process. However, disposable lenses are more expensive than daily wear lenses.
Whatever your need, there's a contact lens for it. Some specialty lenses are made for specific visual conditions while others are manufactured for cosmetic and convenience needs. Most come in both soft and RGP materials.
- Extended Wear lenses, available in either soft or RGP lenses, are worn round-the-clock before they must be cleaned. They offer the advantage of waking with clear vision (and not having to insert contacts lenses each morning) and the convenience of weekly rather than daily cleaning, but have a history of a higher rate of complications. That's because organisms that lead to eye infections can better thrive in an environment without nightly cleaning and the reduced levels of oxygen permeability that come with most extended wear lenses.
Most extended wear lenses can only be worn for up to 6 continuous nights because of FDA decree resulting from problems associated with these lenses. However, the FDA recently approved two types of extended wear lenses to be worn for up to 30 nights of continuous wear. Both the Focus NIGHT & DAY (made by CIBA Vision) and PureVision (by Bausch & Lomb) lenses are made from a revolutionary, new silicone hydrogel material that supplies six times more oxygen to the eye and 40 percent more oxygen than the minimum threshold recognized by independent researchers for overnight wear of lenses. The properties of the lenses are also believed to help minimize deposit buildup over time.
- Toric contact lenses are specifically designed to correct astigmatism, which distorts vision because of an irregularly shaped cornea or lens. Toric lenses, available in both soft and RGP materials, compensate for this irregularity by having different powers of correction at different points on the lens and by being both round and oval at the same time. They offer the convenience of crisp vision without having to wear glasses but must be custom-made, since everyone has a differently shaped cornea and lens.
- Multifocal contact lenses work just like bifocal, trifocal and progressive eyeglass lenses – different parts of the lenses correct vision at different distances. These contacts are available in both soft and RGP materials and primarily designed for people with presbyopia who prefer contact lenses to wearing glasses. Due to variances across prescriptions and manufacturers' products, most multifocal RGP lenses are made-to-order, while soft lenses are more likely to be available in your eyecare provider's inventory.
There’s also a therapy called "monovision" that can also help presbyopes who prefer contact lenses in which different "strength" contact lenses are used in each eye. Usually, the dominate eye is corrected with a single-vision contact lens for distance while the other eye gets another single-vision contact for near vision. This therapy takes some adjustment, but 80 percent of patients get accustomed within a few weeks, as the brain learns to pay attention to the clear image (whether it's near or far) and ignore the blurry one. However, some monovision patients have trouble driving at night and may require eyeglasses while also wearing the contacts. Some wearers combine multifocal and monovision lenses.
- Scleral (or Haptic) contact lenses cover the entire visible white part of the eye (the sclera), as opposed to just the cornea. These are often used to treat
keratoconus. Since they are rigid, they provide excellent optics and are easy to handle. They are also more comfortable than rigid corneal lenses because their edge is under the lids. However, many are made of PMMA so they are not oxygen-permeable.
- Protective tints are contact lenses that absorb ultraviolet radiation to protect eyes against overexposure that can lead to macular degeneration,
cataracts and vision loss. The major UV sources are the sun, electronic monitors, and some light sources. Some contacts come with tints that absorb UV rays. These lenses filter out the harmful radiation better than sunglasses, which allow light under and around the frames. They are usually recommended to patients with macular degeneration, who have had cataract surgery, who take medications that increase sensitivity to light or who work outdoors. However, they should be considered by any contact lens wearer.
- Cosmetic tints are contact lenses that cover your natural eye color to change or enhance it. These lenses may be transparent, with a mild tint, or opaque with a heavy tint (which are not advised for night driving). They are available in soft and RGP materials, but since soft lenses are typically preferred because they cover the entire iris, unlike RGPs. These tints can be added to contact lenses with no prescription, but still require a proper fitting by an eyecare provider. All tinted lenses require the same care as other contact lenses and even if your lenses have no corrective power, you will need to be evaluated and fitted properly by an eye doctor.
Contact Lens Care
On the naked eye, tears continuously cleanse the cornea by washing away a film of microorganisms and protein. This film coats sterile lenses as soon as they make contact with the eye. But tears cannot wash away the debris trapped under the lens or in the porous materials and if lenses are improperly cleaned or kept too long, the buildup of organisms such as bacteria, fungi, yeast and mold can lead to infection and discomfort.
Meanwhile, protein deposits that can cause discomfort adhere to soft contact lenses at an alarming rate – deposits are detectable after less than 1 minute of wear.
Simply washing and rinsing lenses in a recommended solution eliminates 90 percent of the microorganisms that threaten your eyes; multi-purpose disinfecting solutions can reduce bacteria, fungi, yeast and molds as soon as contact is made with the lens, without any rubbing. Along with the directions of your lenses and lens care products, follow these cleaning rules:
- Wash your hands thoroughly before handling your contacts.
- Clean, rinse and disinfect lenses stored for more than 12 hours.
- Wash, clean and air-dry your contact lens cases regularly.
- Replace your contact lens case every 3 months.
- Avoid handling your contacts after washing your hands with cream or moisturizing soaps - they will leave an oily film on your lenses.
- Never wet your contacts with your saliva or tap water, both contain bacteria and infection-causing microbes.
- Never use homemade saline solution - they might not be sterile or balanced and can be a danger to your eye.
Cosmetics can cause eye irritation. If you use makeup, follow these steps to protect your eyes and your contacts:
- If you wear soft contact lenses, insert them BEFORE applying cosmetics.
- If you wear RGP lenses, insert them AFTER applying cosmetics.
- Remove any contact lens before removing cosmetics.
- Avoid lash-extending mascara because the fibers can get under the contacts and injure your eye.
- Avoid waterproof mascara. It stains soft contacts.
- Use hairspray before inserting any type of contact lens.
- Use oil-free moisturizers to avoid smearing your lenses; do not handle your lenses after using moisturizer.
- Take extra care when using false eyelash adhesive, perfume and nail polish. They will permanently damage contacts.