Contact lenses are small, thin discs of plastic that rest in place on the eye. These corrective lenses are held in position by the natural moisture of the cornea.
Contacts are used as an alternative to eyeglasses and have several advantages over them. They are considered to be more comfortable and convenient as well as providing better peripheral vision.
Because the lens rests directly on the eye, size differences that sometimes occur with glasses are minimized giving a more natural appearance to what is seen. They also have the advantage of providing more natural, distortion-free vision, unaffected by weather (raindrops and snowflakes), steam, or glasses’ frame obstruction. In the presence of high myopia (extreme nearsightedness), aphakia (loss of natural lens caused by cataract surgery) or corneal diseases, contacts correct vision better than glasses.
On the flip side, because contacts are a foreign substance in the eye, such complications as tearing, redness, itching, corneal abrasions, or infections can occur more often.
Plastic lenses were actually first introduced in the 1940s, although many innovations and improvements have been made since then. Contacts have become increasingly popular since 1972 when soft lenses were first introduced.
However, the idea has been around for centuries. Leonardo da Vinci is credited with the concept around 1550, but it was a scientist in Switzerland who actually made the first contact lens out of glass in 1887. These lenses were not successful because the human eye could not tolerate them.
Contact lenses require a prescription. After that, they can be purchased from several places, including your eye doctor, a vision care center, or even a mail-order business. Mail-order businesses can be the least expensive source for purchasing contacts because of the discount they receive from manufacturers for buying in bulk.
Although buying from your doctor may cost a bit more, he is also more concerned about the health of your eyes. If contacts are purchased from someone other than your own doctor, there are a couple of things to keep in mind.
Do not continue buying the same lenses based on an old prescription. Yearly exams should be scheduled so that your doctor is able to keep abreast of any changes. Complications, if caught early are usually reversible. The second thing to watch out for is not to allow a seller to talk you into buying a different kind of lens than one your doctor has recommended.
Contact lens prescriptions are more complex than those for eyeglasses because they require measurements for power, curvature, diameter, and thickness, as well as for the selection of design and material. For that reason, many states require only eye doctors to write prescriptions while others allow opticians to prescribe contacts. Although there are many varieties, there are two main categories: hard and soft.
Hard contact lenses were first introduced in the 1940s. They can correct nearsightedness, farsightedness, and astigmatism. Hard lenses were much improved during the 1970s when a gas-permeable model was developed. These lenses are hard but allow air to flow through them to the eye. They are more flexible than the earlier hard lenses, and generally fit better. Hard contacts are made with computer-controlled lathes and can be ground to correct various vision problems. They also can be made into bifocal lenses and can be used to correct corneal problems that cause vision to be distorted. If proper care is taken of them, they can last a decade or more.
Rigid gas-permeable lenses were developed in the late 1970s. They are slightly more flexible hard contacts that are more porous to oxygen. They offer excellent correction for a wide range of vision problems. They are usually easier to adapt to, as well as being more comfortable and durable than soft lenses. For some people, “gas perms” may provide sharper vision than soft contacts, but they do have several drawbacks. They have to be worn regularly. They can also slip off the cornea and pop out of the eye more easily than soft contacts. It is also easier to get dust under them, which will irritate the eyes.
Soft contact lenses are available to correct nearsightedness, farsightedness, astigmatism, and presbyopia (the inability to focus at near distances). They can also be made into bifocals. Soft contacts are sometimes called hydrogels because they hold water, which is what makes them so soft and comfortable. The water content varies from about one-third to three-fourths of the lens, depending on the material. Soft lenses also allow oxygen to pass through the plastic to nourish the cornea. Although more comfortable to wear and easier to adjust to, they are not nearly as durable as the other types.
To tell if the contact is inside out or not is important. Putting them in backwards may not affect the sharpness of vision, but it can irritate the eyes. In fact, if the eye begins to hurt as soon as the contact is inserted, it is likely inside out.
There are two ways to check without putting them in. The first is to hold the lens on the tip of the finger and look closely at the rim. If it is pointing straight up like the edges of a bowl, it is turned the right way; but if the edges are flared out like a walking path along the edge, it is inside out.
The second way to tell is to put the lens on the crease line in the palm of your hand and gently start to cup your hand. If the edges roll neatly toward each other, like they are forming a tiny taco shell, the lens is right side out but if it starts to fold backwards, away from the center, the lens is inside out.
There are several kinds of soft contacts available:
- Daily wear, or conventional are thin plastic lenses that conform to the shape of the eye. Like other soft contacts, they cannot correct some common vision problems, as a high degree of astigmatism. As the name implies, they are designed to be worn while awake but taken out before going to sleep. They need to be cleaned each day and replaced yearly.
- Disposable, or frequent-replacement lenses are thinner and more porous to oxygen than daily wear lenses, which makes them even more comfortable to wear. As the name suggests, these lenses are worn only for a short time and then discarded. Some are designed to be changed daily. Others can be worn, during waking hours, for one to three months; but it depends on the design, the material, and how well they are taken care of. They are more prone to surface buildup, so need to be cleaned daily.
- Extended Wear Lenses are usually disposable and are designed to be worn for more than 24 hours without having to remove them. Because these lenses are designed to provide adequate oxygen to the cornea during sleep, they are approved for up to seven days of wear. However, most eye doctors do not recommend extended wear lenses regardless of the material from which they are made because the eyes receive less oxygen during sleep while wearing the contacts. Furthermore, these lenses greatly increase the risk of serious eye infection because of the bacteria buildup that increases during the night. Disposable extended-wear contact lenses have been available since the late 1980s. They are designed to be placed in the eye, worn for about a week, and then thrown away. Lenses that are disposed of after one day of use were introduced in the mid-1990s.
Flexible-wear Contact Lenses can occasionally be worn overnight but they are not designed to be worn constantly.
Bifocal contact lenses are available in both hard and soft lenses and contain two prescriptions to correct refractive errors. Crescent bifocal lenses are similar to traditional bifocal spectacles in that the prescription for distance is at the top part of the lens and the prescription for close vision is in a crescent segment at the bottom. The lenses are either weighted or truncated (flattened) at the bottom to keep them from rotating out of position. Concentric bifocal lenses differ in that the close vision prescription is in a ring around the inner circle of distance vision prescription. This design circumvents the problem of rotation.
Monovision contact lenses are those with a reading correction in one eye and a lens with distance correction in the other eye (usually the dominant eye). The brain may adjust to this unequal correction, but vision will be a bit more blurry than normal. Generally, there will be a sharper vision with conventional bifocal contact lenses. Modified Monovision Contact Lenses is an option where bifocal contact lenses are worn in the nondominant eye and a contact lens for distance correction is worn in the dominant eye. This allows for use of both eyes for distance but only one for reading.
Toric contact lenses are soft lenses that correct astigmatism. In the past, astigmatism had to be corrected with hard lenses because the soft ones tended to mold themselves to the irregularities of the cornea. The toric lens provides the correction of the hard lens and the comfort of the soft. Like bifocal lenses, toric lenses require a predictable, nonrotating position in the eye. They are often weighted or truncated to discourage rotation. Toric lenses are typically more expensive than other types.
X-Chrom lenses are contact lenses for those with red/green color blindness. It is a deep red lens worn in the nondominant eye and intensifies the color of red and green objects. This allows the nondominant eye to feed information to the brain about colors it could previously not determine. The dominant eye continues to relate information about colors that it normally sees. The lens is not a cure for color blindness, but is an aid in the improvement of color perception.
Cleaning is very important in order to avoid the risk of infecting the eyes. Most doctors will give a starter kit with the lenses.
For soft lenses this usually includes a bottle of multipurpose rinsing, cleaning, and soaking solution that kills and removes bacterial buildup.
For rigid gas-permeable lenses, a separate cleaning solution and rinsing-soaking solution is usually needed.
Make sure that all products are mercury-free. This is a very toxic metal that can have some alarming side effects. Your eye doctor will be able to tell you which products are mercury-free.
Although each kit usually contains instructions, the following tips may be useful:
- Before handling the contacts, wash your hands with a mild soap. Avoid creamy soaps that leave a film on the hands and this will transfer to the lenses. Rinse and dry your hands with a lint-free towel.
- Never use water or saliva to clean lenses. Both contain microorganisms that can cause infection. There are certain amoebas that can enter the eye from water, so never use tap water. One such microbe is “Acanthamoeba” which can cause an incurable infection. Always use a sterile cleaning solution, especially that recommended by your eye doctor.
- For daily wear and rigid gas-permeable lenses, an additional protein-removing enzyme cleaner is recommended.
- With soft contacts, some bacteria can penetrate the lenses. Therefore, after rubbing each lens in the palm of your hand for a few seconds, soak the lens in a cleaning solution for at least four hours before wearing it again. This generally kills most of the remaining bacteria.
- Clean the lens case daily with the sterile rinsing solution and allow to air dry. Replace the case every three months.
Disinfecting contact lenses can be accomplished by one of three basic methods: heat, chemicals, or a peroxide oxidative disinfectants.
- Heat systems, with high temperatures, destroy bacteria on the lenses. Lenses are first cleaned and rinsed and then placed into a heat unit where the bacteria are destroyed. Using heat to kill bacteria is a fairly quick process, and there is no need to use solutions that contain preservatives and chemicals. The downside is that it can cause coatings to build up on the lenses and heat cleaning is not safe for all types of lenses.
- Chemical disinfectants kill bacteria over a period of several hours. Although they are effective in cleaning and disinfecting, they can cause allergic reactions.
- Peroxide oxidative disinfectants were developed in the early 1980s and are considered to have some advantages over heating or chemicals cleaning systems. Although the disinfectants are based on a hydrogen peroxide solution, they have built-in neutralizers that break down the peroxide so that it does not remain on the contacts. Because of the neutralization, there are no chemical residues nor is it necessary to heat the lenses.