• Contact Lens Types

    By John Dick ABO, FNAO

    What Contacts Are Best Suited to You?

    Lifestyle Considerations

    The reasons we wear contacts are varied. We may like the fact we don’t have to worry about glasses slipping down our noses, lenses popping out or making those annoying sore spots on our noses or behind our ears. We might see better with contacts (which sit directly on the cornea) versus glasses when at times you may perceive a swim effect in prescriptions with higher powers. Contacts give us the convenience of simply putting them in before we start our day and simply taking them out before bed, and in some cases we enjoy continuous wear contacts.

    With the risks associated with poor cleaning regimens and over wearing lenses reduced thanks to the advent of better materials, we hardly give our lenses a second thought. They have been allowed to become a seemingly simple and easy way to correct our vision problems while at the same time providing a multitude of benefits such as ease of use, lifestyle demands and cosmetic benefits.

    Comfort and Activities

    Lifestyle demands may very well make contact lenses the best modality for correcting your vision especially if you don’t want corrective refractive surgery such as LASIK or PRK. If you’re an active adult and enjoy outdoor activities such as golf, hiking, skiing and any activity where glasses may become cumbersome, the benefits of wearing contacts become apparent.

    Occasionally, patients may work in environments which facilitate the need for contact lenses. For example, occupations requiring the use of safety glasses or goggles become prime candidates for contact lens wear. Most patients requiring safety glasses do not enjoy having to lug around the extra weight of ANSI compliant safety glasses (which requires a minimum 3.0 center thickness). Wearing contact lenses under a lighter and more streamlined pair of safety glasses without a prescription allows the patient to be more comfortable in their working environment.

    Cosmetic Considerations

    Occasionally, the reasons for wearing contact lenses may be more cosmetic. Patients may feel self-conscious especially if they have a high powered prescription. Bottle thick lenses are not an attractive option for most patients. Additionally, these high powered plus lenses for hyperopic patients (those suffering from a high degree of farsightedness), will magnify the appearance of the eye giving it a bug like distortion. The opposite is true for those with high powered minus lenses for myopic patients (those afflicted by a high degree of nearsightedness). These lenses have the tendency to minify (make smaller) the appearance of the eye making it appear as though the patient may be disinterested in their surroundings, or simply aloof.

    Whatever your reasons for wearing contacts there has never been a better time to be a contact lens wearer. Manufacturers have conducted extensive studies to better suit the needs of patient taking into account lifestyle, age and ocular history. As a result, manufacturers are better able to meet the needs of their patients whether they suffer from presbyopia (need for bifocals), high powered myopia (near-sightedness), high powered hyperopia (far-sightedness), astigmatism or if you simply want to change your eye color and see well while doing so.

    Are You Simply Too Busy?

    Let’s face it: time has become a commodity. If you work irregular hours, attend school, are raising children, caring for an elderly friend or loved one or doing all of these things at the same time, our time has become a precious resource. We are required to manage our time wisely while trying to juggle different aspects of our lives which are time consuming in themselves. We are simply a society on the move. Luckily, contact lens manufacturers have developed contact lenses which will accommodate even the most hectic of schedules. Daily wear contacts are designed to be worn all day and then simply thrown away. These contacts are available in a variety of fitting modalities and prescription powers. Wearing daily lenses will often reducing the complications associated with extended wear.

    Daily Disposables and Limitation of Complications

    One such complication is the build-up of proteins, allergens, bacteria and other debris on the contact surface. Proteins found in lachrymation (the tearing process) are comprised of over 500 proteins. These proteins fall into two sub categories: native and denatured. Native proteins help to provide nutrition and support the processes of the cornea tear film (the thin tear layer covering the surface of the cornea). Denatured proteins are those whose bonds have broken down and are simply debris. If contacts are not cleaned properly, they leave behind a white, milky residue. This is akin to the protein found in egg whites. When an egg is exposed to extreme heat, such as in the process of cooking, the proteins contained within the egg white will turn completely opaque. This same process, minus the effect of extreme heat, occurs to our tears when they become denatured. These denatured proteins will attach themselves to the contact surface. With planned replacement lenses (those not changed daily), these lenses will begin to form protein deposits on the surface.

    Protein deposits are long chains of denatured proteins visible with the naked eye. If planned replacement lenses are worn continuously without observing an adequate cleaning regimen, these deposits will begin to reshape the surface of the cornea. One-third of the refractive ability of the eye resides with the cornea. When the cornea becomes misshapen, distorted vision occurs. A build-up of protein deposits will cause light to scatter as it enters the cornea inducing what is known as irregular astigmatism. This can be a very difficult problem to correct and it may take years if ever for it to resolve. Wearing daily disposable lenses eliminates this potential and preserves ocular health.

    Preventing Conjunctivitis

    Bacteria, viruses, allergens and debris are also well known for creating complications with planned replacement lenses. If a lens has a surface defect and is not cleaned properly it is ripe for colonization of bacterial growth. Bacterial and viral conjunctivitis is an inflammation of the conjunctiva — the tissue covering the inside of your eyelids and white part of your eye (sclera). If bacteria or viruses are present they may invade this tissue causing an inflammatory response. Bacteria and viruses may get into your eyes through having contact with infected surfaces. An example of common contaminated objects would be the following: hands, washcloths, towels, cosmetics, false eyelashes, and soft contact lenses. If planned replacement lenses are not cleaned properly they will become refuges of bacteria, debris, proteins and viruses. Symptoms for these types of conjunctivitis include: swelling, itching, redness, watering eyes, discharge of pus and sensitivity to light. This complication can be very uncomfortable and in extreme cases may cause blindness. Once again, since daily disposable lenses are thrown away at day’s end, the risk of these complications becomes minimal.

    Greater Amount of Oxygen

    Another great advantage of daily disposables is the amount of oxygen they allow the cornea to receive. Oxygen is very important in maintaining corneal health. It allows much needed nutrients to permeate the corneal tear film and preserve the homeostatic balance necessary to keep it healthy. In the case of planned replacement lenses which are sometimes not cleaned well, the pores responsible for allowing oxygen to reach the cornea is prevented from getting to where it needs to go. This causes the eye to undergo an autoimmune response to correct the problem. Blood vessels carry oxygen. The cornea is an avascular tissue (meaning devoid of blood vessels). This lack of blood vessels keeps the pathway light travels (the visual axis) clear in order for clear vision to occur. When deprived of oxygen, the body tries to correct the problem through growing new blood vessels. This is known as corneal vascularization and will cause problems with vision in advanced stages when these new vessels cross the visual axis and scatter light as it enters the eye. This imposition of vessels prevents an unaltered path of light from reach the retina where the process of transmittance of images to the brain begins to take place making perception somewhat difficult and limiting the quality of one’s vision.

    Planned replacement lenses have been on the market for decades. They still work well for patients who responsibly care for their lenses or have time to observe proper cleaning regimens. However, if patients have a particularly busy schedule, aren’t always hygienic or simply forget and sleep in their lenses on occasion, daily disposable lenses are definitely the way to go. Your eye doctor will generally assess your personality to some degree and will make recommendations based on what lenses will serve you best, but it’s important to provide your eyecare professional with information about your lifestyle so they may make an informed decision.

    Which Lenses Are the Ones For You?

    There are multitudes of modalities for correcting every vision problem imaginable. Do you suffer from a high degree of nearsightedness or farsightedness? Do you have trouble with astigmatism? Do you require bifocals to read? There is a lens to address each of these problems and allow you to have the vision you desire. Those patients who have extremely high-powered prescriptions and don’t want the hassle or embarrassment of dealing with thick lenses that magnify or minify the eye, manufacturers have created aspheric lens designs to meet these needs. Examining the word “aspheric” we know that the prefix “a-” means not and, of course, the rest of the word “spheric” means spherical. Literally, the word “aspheric” means “not spherical.” Now that we have semantics out of the way, exactly what does this mean? Think of a ball. It’s spherical in shape, right? This spherical characteristic in optical terms is referred to as the radius of curvature. This radius varies depending on whether a lens is convex in design (used for farsighted patients), or concave (used for nearsighted patients). Convex lenses are akin to having two prisms stacked base to base. They are thicker in the center and thicker toward the edges. Concave lenses are just the opposite. These lenses are similar to having to prisms stacked apex to apex. They are thinner in the center and thicker at the edges. With contact lens design, high powered prescriptions have a tendency to fit a little more snuggly around the lens edge. Manufacturers have been able to design a lens which maintains the radius of curvature beginning in the center on a flatter base as it radiates toward the periphery. Not only does this translate to a better fitting lens, but it also allows a wider field of view as one approaches the periphery since the edges don’t have as much curvature. So, not only do these lenses feel better throughout the course of wear, they also allow you to see well. Manufacturers have captured the attention of the public by stating these are HD lenses similar to the picture quality you get from your high-definition television.

    Toric Lenses Correcting for Astigmatism

    Astigmatism is another area where vast improvements have been made. Astigmatism results when the cornea has an irregular shape cause light to separate as it filters through the cornea causing it to fall at two different foci (points of focus) at the retina. One plane of light will be corrected by your prescription for either farsightedness or nearsightedness and other plane (referred to as cylinder) will correct for the astigmatism. This correction is situated at right angles to one another. It’s extremely important for contact lens designed for astigmatism (referred to as toric lenses) to stay in place. If these lenses move as you blink or gently rub your eye, visual acuities will temporarily be comprised until the lens settles back into place. This process is known as the rotational recovery period. Eyecare professionals try to select lenses which will not only fit well, correct your astigmatism in the correct plane, but will also remain stable during the course of wear. Toric lenses are held in place by a weighting process referred to as prism ballasting. This weighting of the lens rotates it to line up and correct the patient’s vision in the necessary planes (referred to as spherical and cylinder) at angles of 90⁰. In the past the prism ballasting was isolated to only one specific area of the lens. Manufacturers have made recent innovations in which this ballasting is often distributed at intervals of 90⁰ in a 360⁰ circle. Not only does this provide the lens with better stability, but it also allows for a quicker rotational recovery time allowing the patient to see clearly with minor inconveniences associated with a rotating lens.

    Presbyopia: When Your Arms Just Aren’t Long Enough

    Patients who require bifocals to read have also been considered in recent development of contacts which provide clear vision at several different focal lengths including distance, intermediate and near. As stated previously, one-third of the refractive ability of the eye resides with the cornea the remaining two-thirds with the crystalline lens. The crystalline lens is held in place by suspensory ligaments known as the zonules of Zinn. These ligaments bow and flex as we view objects at different focal lengths such as distance and near. This process is referred to as accommodation. As we age the ability to flex this lens begins to diminish beginning at about age 40. The amount of ability this lens possesses to flex is referred to as the amplitude of accommodation. From age 40 to age 60 this ability to accommodate without assistance becomes non-existent. The inability to accommodate and view objects up close is referred to as presbyopia (literally translated as “old man eye”), or more in more kind terms “maturity.” .In years past, patients were often limited how they dealt with this loss of accommodation. When wearing contacts, they either had both eyes corrected for distance and wore reading glasses with their contacts or opted for a process called monovision. With monovision, the dominant eye was corrected for distance whereas the non-dominant eye was corrected for near vision. This is still in practice today. However, some patients experience difficulty adjusting to this process since it somewhat inhibits depth perception as the eyes work in tandem (binocularly). In recent years, contact lens manufacturers have designed what are termed “bifocal” contacts. These lenses are designed with concentric rings of power. Some are designed using the monovision process while others correct both eyes using these concentric rings. This system allows both eyes to perceive objects in the same manner simultaneously without sacrificing depth perception. The concentric zones of power also assist the patient in seeing well in the intermediate areas where patients may use electronics such as computers and other personal media devices. Not so with other forms of correction. Some lens designs may only allow clear vision at the near point or distance focal lengths. The only consideration which may be a drawback to using such lenses is low lighting situations. As the pupil expands, attempting to allow more light into the eye, the concentric zones may become more prominent and cause peripheral distortion.

    Bifocals or Multifocals or Progressives? What’s the difference?

    Bifocals are multifocals (so are trifocals and progressives). They are all for people with presbyopia. Since some contacts correct for distance, intermediate and near distances, they are more beneficial than traditional bifocal lenses which only correct distance and near points (minus the intermediate). This is accomplished by creating gradually increasing concentric zones of power. It assists the patient in having a little wider amplitude of accomodation and since many of us use computers or other media devices these days (which typically sit a little outside the range of a bifocal) the multifocal lenses are more convenient.

    The Importance of Ocular History

    Eyecare professional also consider ocular history when fitting the proper contacts for their patients. These may include age, level of tearing and quality of tear production. For example, menopausal women will not produce the abundance or quality of tears they once did. This may make contact lens wear uncomfortable since the corneal tear film needs to be constantly refreshed with tears to maintain ocular health and comfort when wearing lenses. Elderly patients who wish to wear contacts may also encounter this problem as well as patients taking certain medications which may inhibit tear production. Luckily, manufacturers are using materials better suited to retaining moisture than at any other time in the history of contact lenses. Hydrogel lenses are one such example. Hydrogel lenses are hydrophilic meaning they are “water-loving.” The lenses hydrate to a greater extent and much longer than traditional contact lens materials which make them ideal for all patients — especially those having difficult with lachrymation (tear production). They often have a super viscous coating applied to them which helps to mitigate the lack of oils and lipids contained within natural tears of those with dry eye considerations. Many of these lenses are designed using a phosphorylcholine material which is highly biocompatible and ionized to attract water molecules and repel denatured proteins. This material is used in other medical devices such as heart stents and other implants since it has the least amount of inflammatory response and rejection.

    Whatever your purpose for wanting to wear contact lenses advances in technology have made them more available to more patients more so now than at any time in the history of contact lens design. Whether you are a teen or parent on the go, an aging patient requiring some help up close, been precluded from wearing contacts in the past or attracted to the cosmetic aspect of lenses wearing contacts have never offered more. Complications which were common in the past have decreased in regularity thanks to advances in contact materials such as hydrogels and phosphorylcholine. Not only will contacts help you to see better, but they maintain the homeostatic balance necessary to preserve good ocular health. This provides peace of mind to the eyecare professional and allows patients not to worry themselves with a medical device which has become commonplace.


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