Darlings among available lens options, high-index materials require basic technical knowledge before properly recommending them.
While their very name implies a stature far greater than mere low-index offerings, the use of high-index lens materials should be based on their features and benefits and how those will address your patients’ needs.
Here are some tips for using these materials that allow eyecare professionals (ECPs)to provide their patients with thinner and lighter lenses, making even stronger prescriptions as attractive and comfortable as possible.
Prepare for Impact
The first decision you must make about the use of any lens material, including high-index, is its level of impact resistance. Your guiding principle here should be nullum afferant detrimentum (cause no harm). If the material has every feature you want except the impact resistance necessary, it’s inappropriate for your patient, so choose wisely.
There are three levels of impact resistance-standard, safety and ballistic. Standard impact materials are used in the eyewear most people wear every day known as “dress eyewear.” Safety impact resistance denotes that the lens material is intended for industrial use or visually risky hobbies. Ballistic impact resistance is intended for military and law enforcement purposes, although it is finding its way into more consumer channels used in tactical eyewear.
When high-index lens materials are categorized as those with an index of refraction of 1.60 or higher, then nearly all of them have standard impact resistance.
The Cost of Being Thin
When patients buy high-index lenses, it’s usually because they want a thinner lens than they would receive with a standard index material. The optician’s dilemma, however, is how much thinness can be offered for the price differential. Saving 0.8 mm in thickness for an additional $75 in cost is probably not what the patient envisioned for thinnr lenses.
One way to have a clearer picture of how much difference may be obtained is to use a chart, table or calculator. An example of a lens thickness calculator can be found online at the continuing education website, OptiCampus.com, which was created by the late Darryl Meister, ABOM, (a longtime Carl Zeiss Vision employee who held multiple patents on ophthalmic lens designs). This handy Internet-based calculator lets you choose a lens material, enter the Rx, frame and pupillary distance information, and then calculate the center and edge thicknesses for a job you’re considering. When you enter all of this information for different lens materials, you will then have data with which to compare their differences. However, it is important to remember that these simple comparisons do not consider lens design such as asphericity.
Lens materials are made by many companies around the globe. Interestingly, most ECPs have never heard of most of these manufacturers, except for perhaps PPG and Corning. Instead, ECPs choose lens materials by index, not by manufacturer. Since this is the custom for lens buying, it is critical that you have confidence you will receive quality materials and products from your chosen lens caster (the company that makes lenses from the raw lens material monomer they buy from a chemical company).
Not all lens materials are created equal, even if they have the same index number. To avoid problems, buy from lens companies you know and trust.
There are some problems that could result when switching someone from low-index lenses to high-index lenses. For example, high-index materials usually have a lower Abbe value, which means that color aberration will be increased, especially toward the lens periphery.
In addition, the high-index lens’s configuration is different from the low-index version, which can cause magnification differences and issues with spatial orientation.
If you are switching the wearer to a high-index lens because it’s what’s best for them, you’ll have to work through these issues. The best way to do this is to mention the potential issues at the time of sale.
Don’t make this conversation negative. Simply prepare your patient that there may be some adaptation issues and that most people adjust in a few days. Also, be sure to express this warning in advance of delivering the finished eyewear. If you don’t, there is no way you’ll convince your patient after delivery that there’s nothing wrong with the lenses or the material.
When you do share these basic issues in advance, your patient will be prepared for the adaptation that might occur and will be ready to take advantage of all the benefits high-index lenses have to offer.
Ed De Gennaro, MEd, ABOM, is director, professional content for First Vision Media Group.
WHERE TO FIND IT:
Corning Ophthalmic 800.821.2020 • corning.com/ophthalmic
PPG Industries, Inc. 800.323.2487 • ppgtrivex.com