contact lens materials
Identify the Right Lens for the Right Lifestyle
Learn how to select the best contact lens materials for your active patients.
BY CARY HERZBERG, O.D., Aurora, Ill.
Contact lens practice over the last 30 years has benefitted from numerous new design concepts and materials. The options facing today's fitter can stagger the imagination in their quantity and diversity. But along with the new advances come new challenges. Contact lens fitters must fit new vision tasks being posed to them, including an aging baby boomer generation with vocational and recreational vision needs that can require close-up accurate focusing of the eyes at multiple near point tasks, and distance needs that require quick response, such as motorcycling.
Additionally, trends in our technology-driven workplace have created demands for computer vision correction requiring new thinking regarding contact lens design. And early learning programs, combined with a reliance on near visual tasks, have contributed to the growth in myopia worldwide.
It's our duty to educate ourselves fully so we can advise patients of any new developments in our exciting contact lens field.
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Be a matchmaker
Innovations in contact lens material technology enables us to match our patients with materials that will help them enjoy their hobbies, improve their on-the-job performances and mitigate the effects of disease. Following are some guidelines for bringing the patient together with a contact lens that will enhance his quality of life:
Computer users. Few occupations today don't involve computer use. Our patients are viewing terminals for eight to 10 hours each day and then "surfing" the Internet after hours at home. Additionally, seniors make up the fastest growth area in new computer sales. We would be mistaken to assume that they're not active computer users. Students are often more involved with the latest in new trends, which may include 3-D optical devices.
All of these groups may exhibit computer vision syndrome (a collection of muscle- and eye-related symptoms that make up the number-one workplace disability). Up to 75% of all computer users suffer some form of this vision-related disorder.
Additionally, secondary dry eye from constant staring and lack of blinking contributes to symptoms of blurring and discomfort for our contact lens wearers. This type of patient may respond to the new aberration-correction hydrogel contact lenses -- especially if she's older than 30 years or has myopia in excess of 3.0D. These lenses naturally correct the asymmetry of the cornea and the result is often extra plus for close work. For the same reason, GP aspheric designs with steeper than "K" fit and eccentricities of .5 or greater will give a bifocal effect at close work. The aspheric design should be manufactured in a low-Dk material. These thin designs need to center with limited movement. A stable material is a must.
For our mature, presbyopic computer users, a full bifocal design or monovision solves near demand, while allowing enough flexibility of focus for all nearpoint visual demands. A translating bifocal design should be made of a high-Dk material -- these designs are thicker and oxygen transmission must not be compromised. A translating monovision design can be a problem-solver if you require high adds. Solve potential dry eye symptoms by using materials that have low wetting angles.
Additionally, computer users can benefit from a light tint to reduce glare and brightness of the monitor.
For the sports minded. Recreational activities, such as football and skiing, can put even the most experienced fitter to the test. Contact lenses should be of a large design (hydrogel or GP) to minimize dislodging and improve comfort. Because patients usually wear contact lenses for many hours, a moderate Dk material minimizes warpage and wettability problems. As for sports where lost lenses can pose a problem, address them with inexpensive disposable lenses.
Another important consideration for your sports-minded contact lens wearers is ultra-violet (UV) coatings. Today's GP and hydrogel materials can come with a UV inhibitor, as well as with a number of color tints, for reducing glare and improving contrast. These will further enhance comfort and performance, as well as protect the eyes.
For instance, hunters interested in improving depth perception can benefit from brown color tints which absorb light in the UV region. Shooters also will benefit from tints that help increase background lighting, which can create sharper distance vision.
Finally, sports-minded patients are perfect candidates for corneal reshaping. Consider fitting a daily wear GP design that's flatter than "K" for a low myope of less than 2.0D. When removed, it allows for many hours of functional vision. These can be simply flat spherical tri-curve designs or reverse geometry lenses of 10 mm in diameter.
In the great outdoors. Like your sports participants, patients who have jobs that require them to be outdoors for long periods (e.g., road construction) should receive contact lenses that have UV protection. Hydrogel lenses provide some UV protection. Additionally, make sure these patients have an optical-quality pair of UV-coated lenses in their sunglasses and that they wear a hat on the job to achieve comprehensive protection of their eyes from these harmful rays.
Special needs for special occupations. You can often answer the visual demands of your patients with tinted hydrogel lenses. Color blindness prevented individuals from acquiring jobs as pilots, as firemen or police officers and working as FBI agents. Now, the Chromagen tinted lens system (Cantor & Nissel Ltd.) can enhance color discrimination in individuals suffering a protan or deutan deficiency, allowing them to pass the color vision test. The only restrictions they will face on the job is that they must wear their lenses when on duty.
Expect more myopes. By the year 2020, the World Health Organization projects the number of myopes worldwide will rise to 5.3 billion, accounting for 60% of the world's population. The myopic patient you treat yearly who averages at least a .50D increase is considered a progressive myope. With this comes risks for numerous eye diseases and conditions, such as retinal detachments and glaucoma. These patients require some form of myopic control.
Fitting GPs on or flatter than "K" and perhaps silicone hydrogels may be our best answer. Fit the lenses with large diameters and high Dk. If our myope shows esophoria or accommodative stress, then we can design the lens with a back surface aspheric design for additional plus at close work. Silicone hydrogels have a flattening effect on the cornea, perhaps aiding in myopia control.
Every myopic patient, no matter what age, deserves the right to learn about corneal reshaping as a lifestyle choice. Ease of use and freedom from daily wear correction are strong incentives. Studies are exploring myopic control exhibited by these designs.
Diseased eyes or iatrogenic problems. Whether caused by keratoconus or refractive surgery, fitting new technologies in contact lens design is enabling positive responses to a potentially sight-threatening outcome. GP corneal scleral designs in diameters of 13.0 mm to 15 mm are giving excellent comfort while taming the irregular cornea. Reverse geometry designs in intra-limbal and corneal-scleral designs are proving to be problem-solvers in refractive surgery cases and penetrating keratoplasty cases that require further corneal rehabilitation.
Normal GP designs, like the human eye, have intermediate and peripheral curves that are flatter than the central base curve. The reverse geometry designs, however, have steeper intermediate curves aiding in centering and placing pressure on the central cornea when flattening is desired. Piggyback designs with hydrogels and GP corneal lenses also have been successful when a GP is needed for vision in a sensitive patient.
As for low vision patients, they can benefit from red, bright yellow or green color tints, which will enhance visual discrimination by improving their contrast sensitivity.
For the just plain busy. Patients who need flexibility in their busy schedules may benefit more from silicone hydrogel lenses. These may include new parents, professionals, teens and college students. Patients can wear these high-Dk designs as daily wear, occasional overnight or 30-day continuous wear. Patients who switch to these lenses after wearing low-Dk/t lenses may experience reversal of negative effects of oxygen deprivation. Because of their low water content, these lenses are stiffer, making correct base curve selection important.
Maintain your expertise
I hope that you enjoy the challenges and rewards of fitting the many commonly prescribed contact lens materials as much as I have. I look forward to working with newer materials as the industry progresses.
References available on request
Dr. Herzberg hails from a three-generation optometric
family. He's an active lecturer, writer, technical consultant to the contact lens
industry and an FDA investigator for overnight orthokeratology lenses. Dr. Herzberg is also a member of the American Optometric Association.
Optometric Management, Issue: December 2004