L&T: Lens Choices

Oct
2007

Thin Is In

By Eric Rollins

Turn on your television any night of the week (or afternoon, for that matter) and you will see ads hawking a myriad of weight loss products. Medical procedures such as liposuction and bariatric surgery are growing at an explosive pace. The New York Times’ best sellers’ list is peppered with books about the latest diet crazes. Let’s face it: Americans have a love affair with slimming down. So it only makes sense to help our patients acquire lenses that are thinner and lighter too.

With all of the great tools available in today’s optical marketplace, we can reduce thickness and weight by 20 to 50 percent depending on Rx factors. Let’s take a look at what’s on the menu for our lens reduction plan.

Index of Refraction
The index of refraction of the lens material used is one of the most important parts of our plan to get thinner and lighter. As the index rises, it takes less of the lens material to bend light to the degree required to achieve the proper refraction. Materials currently on the U.S. market in spectacle lenses run from 1.50 for standard index plastics to 1.74 in ultra-high index plastic. Some glass lenses used in other countries have indices of refraction of 1.8 and 1.9, but these products are not in use in the U.S. due to impact-resistance regulations. Gary Dezell, the manager of Marcella Optical Laboratory in Cedar Rapids, Iowa, advises his customers to use ultra-high index lenses to get the thinnest and lightest product. “We use a lot of 1.70 index lenses. They are aspheric and lightweight, and can be ground thinner than a 1.74 index lens. We’ve had great luck, especially with high minus lenses.” Dezell adds, “1.70 is also a terrific lens for drilled rimless mounts.”

Another factor to consider is lens strength. Polycarbonate and Trivex offer your patients a safer lens and in lower powers will rival the thinness of ultra-high index materials. There is also a significant cost savings that may be attractive to consumers. Savvy eyecare professionals should match the benefits of thinner and lighter lenses with their patients’ budget needs to come up with the best value equation.

Both polycarbonate and Trivex also have lower specific gravities than other materials, so are lighter in weight for most Rxs. Both materials are good choices when weight is a primary concern.

 Asphericity
Asphericity means the surface of the lens is not round (like a basketball), but flattens as it moves from the center of the lens. Traditional aspheric lenses have a central “button” that is spherical, but become aspheric moving to the periphery of the lens. The typical button size is about 12 millimeters in the center of the lens. The asphericity on the outside of the lens allows the lens designers to flatten the curvature of the lens, give clearer vision on off-axis viewing and at the same time make the lenses thinner.

Newer technology has improved the designs of aspheric lenses. Computerized machines from manufacturers such as Rotlex utilize eye mapping, transferring information to the designing equipment so that the entire lens is aspheric, including the center. The new designs provide better optics throughout the lens surface for all viewing angles. This technology optimizes vision through all parts of the lens by eliminating unwanted astigmatism and distortion. The lenses are also thinner than spherical lenses. In the case of plus-powered lenses, the difference can be striking, as much as 30 percent thinner.

Bob Westlake, operations manager of Harbor Optical, a wholesale laboratory in Traverse City, Mich., is a strong proponent of aspheric lenses. “Aspherics give improved optics in the peripheral areas for off center viewing,” notes Westlake. “Aspherics reduce the magnification of the eye for plus-power lenses and reduce the minification of minus-power lenses. Aspheric designs also allow the lens to be flatter, making a thinner profile. One additional benefit is the profile of the lens actually fits many frames better, allowing for a stronger mount.”

Minimum Effective Diameter (MED)
Don Granner of Advanced Eyecare Professionals in Hastings, Mich., recommends using the Minimum Effective Diameter, or MED, method of thinning lenses where possible. First brought into use about 35 years ago, before the advent of high-index materials, the concept behind MED is to eliminate decentering the lenses by matching the patient’s pupillary distance with the frame’s pupillary distance.

The frame pupillary distance (frame PD) is found by adding the eye size and the bridge size. For example, a frame with an eye size of 48 and a bridge size of 16 would have a frame PD of 64. When this frame is used for a patient with a 64 mm papillary distance, the lenses would not have to be decentered.

Since the decentration is minimized or eliminated, overall thickness is minimized in every material choice. This is also true whether the patient is myopic or hyperopic.

“MED fitting is still a wonderful tool for any strong Rx,” says Granner. “In the days before lens implants following cataract surgery, it was about the only technique we had to reduce thickness for aphakic eyes. Now there are other lens materials and designs to help reduce thickness, but MED is still a fantastic place to start. It will reduce the lens thickness on any Rx regardless of power. It is also the only way to reduce lens thickness without adding anything to the cost.”

Edge Treatments
Two general areas of lens treatments are commonly used in the market to make lenses appear thinner: rolled and polished lenses, and edge color treatments. Both have greater benefits for minus-power prescriptions due to the thicker edges.

Roll and polish has been around for years. Rolling the lens abrades the back edge of the lens in a semi-circular fashion. This actually does reduce the thickness of the lens, as material is removed from the thickest part of the lens. While the polish doesn’t actually make the lens thinner, it does improve appearance and can give the illusion of being thinner. The downside of a roll and polish can be reflective internal light rings. With high-performance high-index and ultra-high index materials now available to reduce thickness, some opticians prefer to go with polished edges only rather than a roll and polish. Edge polishes are now common in both a high gloss and satin finish. If roll and polish is chosen, a good solution to the internal concentric light ring problem can be an edge color treatment.

Edge color treatments have developed considerably in the past 20 years. The colors are much more durable and easy to apply, and the amount of time required to perform the color treatment has been significantly reduced.

The easiest method utilizes coloring pens. There are numerous manufacturers of coloring pens that conceal thickness by matching or enhancing the color of the frame, making the lens less visible. Scott Rector, co-owner of Professional Optical in Petoskey, Mich., uses the BPI products with his patients’ eyewear. BPI currently markets a collection of coloring pens called “Touch of Tint,” a set of six pens, and a “color blender” pen costs $180 and will cover about 150 to 300 lenses. Rector says the color pens “are easy to use, can be done quickly and effectively, and are a nice fashion touch for our patients.”

Other vendors of color pens include OptiSource, Hilco, OMS, Stormin’ Norman’s and Breitfeld & Schliekert. A wide variety of colors are available and some manufacturers will even produce custom color pens. Other manufacturers market paints for the same purpose.

Frame Selection
Current frame styles give optical professionals a great opportunity to keep lenses thin. Mid 1980s styles were oversized, with 60 millimeter lenses common, and many sunglasses even larger. Now that we are seeing most styles in the 50 millimeter range and smaller, we have a much easier job to minimize lens thickness. There are still some additional steps we can take in frame selection to keep lenses as small as possible.

Rector believes frame selection is still the number one deciding factor in reducing lens thickness. “If you start with a correctly shaped small frame, you will end up with the thinnest lenses every time. Then it’s just a matter of how much the patient is willing to spend to go with the other tools we have to reduce lens thickness, such as high-index materials and aspheric lens designs. If you start with a large frame, the lenses will be thicker and you will need to use every trick you know to try to reduce the thickness.”

Frame Shapes
The best shapes to use to minimize lens thickness are roundish shapes. Slight ovals and square-like shapes work as well. Shapes to avoid for thickness reasons are shapes with particularly long ED measurements, such as “pilot” and “navigator” shaped frames. Frames with narrow bridge sizes also tend to require more decentering leading to thicker lenses. Many manufacturers produce frame designs with the specific intent to reduce lens thickness. Some of the ideas utilized include carrier frames inside the main frame and wide front pieces to make frames appear wider, and thick plastic or metal eyewires to mask lens thickness.

Tracing frames for the thinnest lens
Labs need to have the frame data sent in to insure the thinnest possible lenses. The more precise the data in the hands of the lab, the thinner the lenses can be. “Electronic transmission works well,” Dezell says, “especially for plus-power prescriptions for thickness control and to expedite the Rxs with anti-reflective coatings that are on many of today’s lenses. Turnaround time is significantly improved. But ideally we’d love to have the frame in hand to insure the thinnest lenses and the best fit.”

The final entree for our deliciously thin lenses is an anti-reflective coating. AR will make the lens appear thinner due to the reduction of reflections and will also offer the patient the best vision. AR is especially valuable with high-index lenses due to the higher percentage of light reflections, as much as 16 percent with the ultra-high index materials.

Now that we have all this information, where do we start? Dave Gohman, customer service manager for X-Cel Optical in Sauk Rapids, Minn., likes to begin with the basics. “Find out as much information as you can about the job. What is the prescription, are there any special Rx requirements, what is the lifestyle of the patient? The lens choice will be based on consideration of all of these details, as well as the lens style needs of the patient such as single-vision or progressive addition lenses. Sometimes the lifestyle needs of the patient will dictate a lighter weight material that is slightly thicker such as Trivex rather than a thinner but heavier and less impact-resistant material.”

We have a wonderful menu of slimming and weight reducing products to offer consumers in today’s optical world. Take the time to discuss their needs and wants, and then take charge of the transaction by recommending the ideal products for their situation. Your patients will thank you for making their appearance (and their vision) the best it can be.



L&T contributing editor Eric Rollins is a 20-year veteran of the optical retailing, manufacturing and laboratory segments. He is president of Rollins Consulting LLC, a Michigan-based firm assisting eyecare professionals in profitability and patient satisfaction. For more information, call Rollins Consulting at (231) 740-2929.

 

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