Introduction and Overview
If you are considering contact lenses for your vision correction, it is helpful for you to know a few things about them, such as the different types of lenses, how they work, what they feel like.
New technology in contact lens materials and design has allowed many people who could never before wear contact lenses to become good candidates for this method of vision correction. From the very young to the more mature patient, almost anyone can wear contact lenses successfully with the right fitting and follow-up care.
The choice of contact lens type is made with the help of your eyecare practitioner, who will consider all the various types of lenses available and your specific reasons for wanting them. The practitioner will also consider your ability to handle the lenses and care for them. Together, you will decide on the best type of contact lenses for your individual situation.
Reasons for Considering Contact Lenses
Contacts move with your eyes, allowing for a more natural, full field of view. There are no frames to get in the way. Most people wearing contact lenses for the first time experience a feeling of freedom and clear vision, without distortions caused by spectacle lenses.
Contacts do not fog up in the rain, and they won’t get splattered by mud, either. There’s nothing out in front of your eyes to get dirty and obstruct your vision.
Contact lenses don’t get in the way of your activities. For sports, they are a great way to help increase your success, because you no longer have to worry about your frames being in your way. However, there are some sports that contact lens wear is not appropriate for, like swimming or diving. Also, any sport that requires safety goggles, like racquetball or handball will still require them with contacts.
Contacts help you look your best. Cosmetic reasons are just as good as any other for wanting to get into contact lenses. Some people just feel that they look better without their glasses, but would also like to see clearly when not wearing them. The answer: contact lenses.
Contact lenses usually provide better clarity of vision than spectacle eyewear, because the distance between the eye and the spectacle frame introduces some optical factors that are not involved with a lens resting on the tear film of the eye.
Many Types of Contact Lenses Available
During the past two decades, contact lens materials, designs and manufacturing technology has given the eyecare practitioner and the patient a lot more choices for vision correction. Contact lenses are available that correct astigmatism (when the eye focuses differently in one meridian than in the other), presbyopia (the difficulty focusing objects up close by most patients over 40) in addition to myopia (nearsightedness) and hyperopia (farsightedness).
Having toric (astigmatic) and multifocal (presbyopic) contact lenses available has made it possible for patients who were never able to wear them before to do so.
Another specific use of contact lenses is to reduce the effects of anisometropia, a condition where some people have very different refractive errors in one eye than the other. Using spectacles to correct anisometropia can be problematic, because lenses of different powers cause different amounts of magnification, and can cause the brain to perceive the size of an object as being larger in one eye than the other, which can cause eyestrain symptoms like headaches and fatigue, and, in severe cases, diplopia (double vision. One variable in the mathematical formula in optics that determines how much a lens will increase or decrease the perceived size of an object is the distance from the eye to the lens. When this variable is reduced to zero by placing the lens on the eye, the perceived size difference also diminishes significantly.
Things to Consider about Contact Lenses
Contact lenses require a longer visit to the eyecare practitioner, because there are extra measurements that need to be taken for proper fit that are not needed for glasses. Follow-up appointments are also required, to maintain your healthy eyes.
Contact lenses require more care than eyeglasses. This is because your eyeglass frames are not directly on the eye, so it’s enough to wash and rinse them with ordinary soap and water. Contact lenses require special cleansers, rinsing solutions and conditioners for you to wear them successfully. They require a daily (usually) care regimen that must be done each time you remove them for the day. The exception to this is extended-wear lenses, which are meant to be worn for a specified time period, (usually a week, two weeks or even up to 30 days). Even these lenses, however, still need to be cared for properly, each time they are removed, unless they are to be thrown away.
Contact lenses usually cost more than spectacle eyewear over the long run when taking into account all of the factors listed above. Most eyecare practitioners want their contact lens patients to have a current pair of glasses as well to provide backup correction when contacts aren’t being worn.
All modern contact lens materials will absorb to a greater or lesser extent the solutions they are disinfected and soaked in when they are not being worn. They can also absorb hair spray or hand lotion; care must be taken that the contacts are not bringing unwanted chemicals or other materials into the eye.
The normal tears in the eye come from glands located in the upper and lower eyelids. The openings for these glands are located just inside the line of the eyelashes. While it is generally safe and reasonable to wear makeup while using contacts, eyeliner should never be applied inside the lash line. Doing so can clog the openings of the tear glands and can cause a problem with the tear film.
Contact Lens Terminology
There are many new terms to learn when you are discussing contact lenses. To help you understand what is meant by certain terms to avoid confusion, here are some of them:
- Rigid Gas-Permeable (RGP) Lenses: made of mostly rigid, oxygen-permeable plastics, these lenses replaced the original hard contacts that were used in the past. They are comfortable on the eye after a short adaptation period, correct most vision problems, are easy to handle and care for, have a relatively long life-span and are available in specialty lens types such as multifocals and those that correct high amounts of astigmatism. They are smaller than most soft lenses, and ride on the corneal tear film. Because they move more with blinking, there is usually more lens awareness initially than with soft lenses.
- Soft lenses: Also called hydrogel lenses, these are soft, very flexible lenses that usually cover the entire cornea so the edges rest on the white of the eye (the sclera). Because the sclera is less sensitive to touch, soft lenses are initially quite comfortable and are easily adapted to. There are several types of soft lenses, including:
- Daily Wear Soft Lenses: Immediate comfort, more difficult to dislodge than RGPs, available in tints, multifocals, and for astigmatism. Allows oxygen to flow through the lens to the cornea. Most of these lenses are meant to be worn daily, removed at night and cleaned, disinfected and stored, then re-inserted the next day. They usually require replacement once a year.
- Extended Wear Lenses: These can be either soft or RGP lenses, and can usually be worn continuously for up to a week without removal.
- Disposable Lenses: These can be worn once, and are then discarded once removed. The wear time can be one day, or extended for up to a week with extended wear-type lenses.
- Planned Replacement Lenses: These are soft lenses, worn on a daily-wear schedule, and replaced every week, two weeks, monthly, or quarterly, depending on the lens materials.
- Spherical Lenses: These have no correction for astigmatism, but correct only near- or farsightedness.
- Toric Lenses: These lenses, either soft or rigid, make it possible to correct astigmatism.
- Multifocal Lenses: These allow mature contact lens wearers to keep wearing their lenses when they begin to become presbyopic; they allow patients to see well both close up and far away.
- Decorative Contact Lenses: Also called novelty lenses, along with several other terms, these are usually lenses that come in fashion tints that can change the color of the eye, or in special designs for use in a costume, as for Halloween or the theatre. Some, usually the ones that change eye color, are available in prescription strengths for vision correction, but most specialty or costume lenses are only available in plano, meaning they have no vision correction.
It is quite common for contact lens types to be combined; for example, you may be fit with a soft, spherical disposable extended-wear lens.
In addition to those listed above, several specialty contact lens types exist, such as those that correct irregular astigmatism or very severe astigmatism, and larger lenses that might be indicated for a patient with a scarred cornea.
How do Contact Lenses Work?
Near- or far-sightedness are corrected in the overall power in the contact lens itself. The lens is placed on the cornea and the tears fill in the space behind it, so the overall power in that front surface is different than it was without the contact lens
Mild or moderate astigmatism correction in an RGP contact lens works by making use of the tears between it and the corneal surface itself. The tears fill in the space between the back of the contact lens and the front surface of the eye, so the combination works as one.
With toric soft contact lenses, the lens itself has the astigmatic correction built into it; to keep the lens from rotating freely with the blink as spherical soft lenses do the toric lens must be stabilized on the eye in its proper position.
More severe amounts of astigmatism may require a specially-made custom RGP lens called a bi-toric. Bi-toric lenses have an astigmatic correction built into them on both the front and the back, and make use of the tear lens as well. These lenses usually do not require ballasting, because the back surface matches the front surface of the eye.
In the case of irregular astigmatism or corneal scars, the tear film works to smooth out the surface so vision becomes much more clear and crisp.
In some instances, the contact lens might be used to gently change the shape of the cornea during sleep so the patient doesn’t need any correction at all during the day. This is called orthokeratology, and ortho-K lenses are specially manufactured for the process.
Contact lenses are a great way to correct your vision. They can contribute to an athlete’s skills, or increase self-esteem. They reduce distortions and other optical issues that are caused by traditional frames and lenses and provide a natural and full field of view.
When fitted properly by an eyecare practitioner and cared for properly, contact lenses are considered to be a very safe and comfortable method of vision correction.
Contacts do cost more than eyeglasses when considered over the long term. The cost of most contact lenses themselves is less than that of spectacle eyewear, but they need to be replaced more often, they require much more care than spectacle eyewear and they require the correct cleaning, rinsing and disinfecting solutions. Accordingly, they also require more time and commitment from the patient.
It is still much easier to put on and take off a pair of eyeglasses than it is to insert contact lenses, then remove and care for them at the end of the day (or other wear schedule). However, they do offer some unique advantages and are usually judged by wearers to be well worth the effort to correct their vision this way.
In general, wearing contact lenses is considered to be quite safe for most patients, as long as proper care is taken. It is important for people to realize, however, that contact lenses are medical devices and require a prescription for legal purchase, even if the prospective buyer “doesn’t need a prescription” for vision correction. A prescription is required to legally purchase any contact lens, of any type, for any purpose whatsoever.
In section two, we go on to discuss more safety issues and keeping your eyes healthy and beautiful with contact lenses.