Not very long ago, it wasn’t uncommon for eye care providers to have to inform a patient that their prescription was out of the range of contact lenses, and they must continue using their glasses. With a surge in technology of materials and designs, however, almost everyone that has corrective vision needs is now eligible to wear some form of contact lens in lieu of their glasses. For many, this now means the freedom of being able to express themselves without feeling self-conscious of their eyewear or worry about breaking or damaging their eyewear during activities such as sports and fitness. There are several different factors that need to be determined when looking at different types of contact lenses: material, design, and wearing schedule.
Over the years, many different materials have been tried. The first contact lenses were “hard” contact lenses, made primarily from a material called PMMA (polymethyl methacrylate), a type of acrylic. While effective at correcting vision, these lenses were extremely uncomfortable, and had little to no oxygen permeability, so overwear of them could cause damage to the cornea from lack of oxygen. These “hard” lenses have now been replaced by Rigid Gas Permeable lenses, or RGPs. RGP lenses are “hard” when compared to their soft counterparts, but unlike the PMMA lenses of yesteryear, RGPs are designed with multiple materials that allow differing levels of oxygen permeability and comfort. Many optometrists dislike fitting RGP’s lenses, as the “trial and error” fitting must often be employed, and is time consuming for both the doctor and the patient. Often you will find that the doctor charges a premium exam fee for fitting these lenses, which incorporates the (typically) multiple followup visits upon which the patient will return for fit adjustments. RGP lenses are useful for very high prescriptions, large amounts of astigmatism (or cylindrical shape of the front of the eye), and to manage an ocular disease called keratoconus, upon which the cornea develops irregular shaping, rendering standard soft contact lenses useless. Soft contact lenses, which are most commonly prescribed, are made from hydrophilic materials and conform to the shape of the eye. They come in a variety of material options made by several manufacturers, and depending on the rest of the ocular correction and lifestyle needs of the patient, will be selected to best match all factors of the patient’s visual needs.
Once it has been determined what material option would be the best choice for the patient’s needs, the design of the lens must be considered. A standard spherical contact lens corrects for a single visual dysfunction, such as myopia (nearsightedness) or hyperopia (farsightedness). Standard spherical contacts can also be used to create a vision correction called “monovision,” where one eye is selected as the dominant eye to wear the distance correction, and the other, non-dominant eye, is undercorrected to allow for clear reading vision. This type of correction is needed when the patient has presbyopia, or needs multifocal lenses, which typically happens between the ages of 40 to 45. If both eyes of a presbyopic patient are corrected for distance wear, the patient must rely on reading glasses to see images at close range, so the monovision correction allows a more complete departure from eyeglass reliance.
A toric contact lens is used to correct an astigmatism, or cylindrical shape of the eye (think of a football). This is another lens that has made leaps and bounds in technology over the years, and there are now multiple options for toric lens wearers. Toric lenses rely on proper positioning on the eye, and even a 10 degree rotation of the lens is enough to cause blurred vision. Toric lenses are weighted at the bottom to help prevent rotation, and the prescribing doctor will be able to see the rotation marks on the lens to ensure that they are properly aligned. Toric lenses may too be used in the monovision correction if a presbyopic patient also has an astigmatism. A new variety of contact lens has recently made headlines as well, which is the multifocal contact lens. These lenses have multiple powers within the lens, usually laid out in a bulls-eye circular pattern, to allow focus at varying lengths for presbyopic patients. By using multifocal contact lenses, presbyopes regain binocular vision for both distance and reading, and lose many of the challenges that monovision corrections can sometimes bring, such as halos and ocular fatigue. Finally, there is a rare and expensive combination of a multifocal toric lens that is made-to-order for presbyopic patients that have astigmatism and wish to use a multifocal correction rather than a monovision correction.
Finally, the last factor that the eye care provider will evaluate is the wearing schedule of the lens. This choice may be made due to health reasons, such as Dry Eye; lifestyle concerns, such as being able to sleep in the lenses; and sometimes on a cost comparison basis. Daily disposable lenses reduce the risk of eye health issues related to contact lens wear in that every day a new lens is opened and inserted, and every night the lens is removed and disposed. This eliminates over-wear, cleaning and disinfection issues, and because they are only designed for a single day’s wear, these lenses are incredibly thin and comfortable, and allow the maximum amount of oxygen permeability. Your doctor may choose this as a beginning lens to introduce you to contact lens wear with minimal risk. The next wearing schedule would be a 1-2 week disposable lens. Some of these lenses are approved for overnight wear, which typically reduces their life down to the one week, whereas with nightly removal they last two.
There are a myriad of brand options available in this wearing schedule. Next is a monthly disposable lens, which again may, in certain brands, be approved for overnight wear. More lens manufacturers are developing lenses in this category, and the options continue to grow for patients that wish to wear monthly disposables. Finally, there are semi-annual and annual lenses, or “conventional” lenses, that come in vials for the patient to wear between 6 months to a year. These lenses are older technologies, and most doctors are reluctant to prescribe them due to advances in wearing comfort and oxygen permeability of newer disposable technology, however many times for cost reasons patients insist on remaining in a conventional lens. Some specialty made-to-order lenses are only available in conventional lens materials, so options can be limited.
Add to this variety of options cosmetic choices such as artificially colored contact lenses, handling tints, ultraviolet protection, and even some specialty sport lenses and theatrical lenses, and you can plainly see that there is a contact lens for just about everyone. If you have ever thought of trying contact lenses but were concerned about the comfort, or have tried to wear contacts years ago but were told they wouldn’t work for you, you might be pleasantly surprised upon your next visit to your eye care professional to find out about the newest technologies and advances in contact lenses.