The variety of high index lenses, including polycarbonate, that have been dispensed in this country has been growing steadily since the late 1980s. Originally conceived as a lens material aimed at the cosmetic needs of high-range myopes, high index lenses have come to mean something quite different to doctors and dispensers in the year 2000.

To better understand what has been a rather remarkable transformation, let's review the current state of the lens market, particularly in regard to the refractive index of lens substrates.

An entirely new sub-category has developed in the field of high index lenses. Called mid-index, the term was made necessary by the growing number of substrates falling in the lower range of high index materials. To differentiate lens materials falling in that mid-range, this category includes materials with an index ranging from 1.54 to 1.57. Everything higher than 1.57 is considered to be high index.

WHAT CONSTITUTES HIGH INDEX?
The conventional definition of a high index lens material is any material with a refractive index greater than glass (1.523) or CR 39� (1.498). During the 1960s and '70s, as eyeglass wearers were switching from glass to new lightweight plastic lenses, even mild myopes learned that the lower index of CR 39 produced thicker edges than what they were used to in glass. In spite of this cosmetic disadvantage, reducing the weight of their glasses by half made the switch worthwhile for most wearers.

Though high index glass had been available for years, it had one major drawback. Because increasing the refractive index in glass requires adding lead, these lenses are heavier than conventional glass lenses and, of course, more expensive. For these reasons, when glass was king, high index was primarily confined to strong minus corrections (seven diopters and higher).

This changed when high index plastics became available, and consumer interest in thinner, lighter eyewear began to increase in the late 1980s--about the same time that TV and magazine ads began touting the benefits of "lighter" beers, cigarettes, and food. And when a 1.60 index plastic became available in 1987, high index lenses came into their own. Before long, doctors and dispensers began offering thinner, lighter lenses to patients with smaller refractive errors, often as low as -2.00 D.

While high index plastic was taking off, poly was not, despite the fact that dress lenses made of poly predated high index plastics. One reason was that the 1.50 refractive index of poly wasn't mentioned when it was introduced. Instead, the lenses were promoted solely on their incredible strength.

Over time, however, its high index properties began to be communicated as a major advantage. That change was a factor leading to poly's current domination of the high index market.

STATE OF THE HI MARKET 
A strange thing has happened to the high index marketplace. Under the traditional definition of high index (corrections of -5.00D and higher) this category would make up no more than 20 percent of the total lens market.

In point of fact, however, high index lenses (including poly) are believed to be approaching 50 percent of all lenses sold in this country. That figure is supported by John Miller, X-Cel Optical vice president, who has closely tracked lens usage as a business-related hobby for years.

There is a sound reason for this seeming discrepancy. It's the same reason that this article might be more appropriate if it had been titled "The Expanding World of Alternative Lens Materials" because that's what has been happening. The reasons for it are best explained by examining the economics involved in today's optical marketplace.

Conventional plastic (CR 39) lenses have served consumers and the professions well since this lightweight material was first used for lenses in 1947. During those early developmental years, plastic lenses were considered a premium lens because they were difficult to process, and consumers paid more money for them.

As labs gradually became proficient in processing plastic, however, the add-on charge was dropped. Then, as glass usage continued dwindling while the cost of glass blanks increased, plastic lenses gradually became a basic commodity. As this happened, profits associated with manufacturing conventional plastic lenses began shrinking.

Consider this: Compared to a dollar in the 1980s, one dollar today is worth about 37 cents. Yet, CR 39 stock lenses in the year 2000 sell for approximately the same price as they did in 1980.

And, in spite of continual improvements in manufacturing techniques, profits from producing conventional plastic lenses have become so minimal that most CR 39 production has been moved to Third World countries. Today, virtually no CR 39 stock lenses are produced in the United States. 

Much the same happened with conventional multifocals in plastic. One exception, however, has been progressive addition lenses.

This explains why laboratory and manufacturer sales reps concentrate their sales efforts on promoting sophisticated lenses such as PALs. At best, laboratories merely trade dollars processing orders for CR 39 single vision or bifocal lenses. The same is true of lens manufacturers.

As eyecare professionals, you and your peers have also moved away from the basics. A number of factors have accelerated this use of premium lenses at the retail level. One reason, of course, has been the professional desire to provide patients with what best meets their visual needs.

Another strong factor has been the rapid growth of managed vision care. Many of you have found that upgrading managed care patients to premium lenses offers the only effective way to generate much in the way of profits under most plans.

This, as much as anything, has accelerated the use of alternative lens materials at the retail level.

HOW POLY FITS IN
The major motivator behind poly's rapid growth during the last four years comes from how this premium material benefits mid-range prescriptions where high index offers few advantages. Take the example provided earlier of the patient wearing -1.25D spheres. Offer that person high index lenses, and the advantages (primarily cosmetic) are minimal at best.

Offer the same patient polycarbonate lenses, however, and they get full ultraviolet protection, unsurpassed impact resistance, and their lenses can be ordered 1/2mm thinner than lenses in any other material.

It's little wonder then that the Polycarbonate Council believes that the growing use of polycarbonate for the broad mid-range of prescriptions in both plus and minus is the primary reason poly's usage has increased so substantially. It's also why the Council predicts the trend to poly is going to continue for some time to come. The use of poly is also accelerating outside this country, and that helps ensure a bright future for its producers.

THE SHIFT CONTINUES
One competitive factor expected to impact the lens market comes from the recent introduction of a new brand name for polycarbonate lenses. The first company to produce polycarbonate lenses (Gentex Optics) is now a wholly owned subsidiary of Essilor, and the company recently launched a major advertising campaign for its polycarbonate lenses under a new brand name--Air Wear.

Several lens companies are now importing polycarbonate lenses produced in countries outside the United States. And, Singapore's Poly-Core, one of the world's largest producers of conventional plastic lenses, recently established a complete polycarbonate production plant in Reno, Nev.

These developments represent a radical turn-around from those years when polycarbonate lenses were solely an American product and one that, for the most part, was either ignored or ostracized in the rest of the optical world. For some time now, the market share for polycarbonate has been considerably higher than all other high index materials combined.

VCA (Vision Council of America, formerly OMA) tracks domestic lens shipments by material, and recent numbers suggest that interest in traditional, uncoated materials is declining.

VCA statistics are derived from voluntary, confidential reports of product shipped within the United States and submitted by full VCA members. The VCA 1999 year-end estimates reported here were calculated from data submitted by February 2, 2000, and show the market share for glass in 1999 to be four percent (not including high index).

Uncoated CR 39 lenses in 1999 were 28 percent thats down from 30 percent in 1998, and coated CR 39 in 1999 were 38 percent, down from 1998's 39 percent. On the other hand, the market share for polycarbonate was 24 percent in 1999 which is up from 21 percent the year before.

HOW HIGH CAN IT GO?
The high in high index continues to get higher. Here's some of what's new.

1.67 vs. 1.66. Both are made from the same material (MR7) and have identical indices. The difference in their advertised refractive index comes from how refractive index is measured in Europe and Asia vs. the United States.

Until recently, the highest index available in plastic has been 1.66, first introduced in 1992. These lenses are currently available in a variety of forms and offer substantial benefits to patients wearing high minus lenses. Lenses in 1.66 are usually only available in aspheric form. They can be ordered in double concave form for extremely high corrections. Currently, two companies offer 1.66 stock lenses with atoric curves on the backside of the lens. Producing aspheric curves on the backside of a 1.66 high minus lens thins edges even more and represent the ultimate in cosmetics for high minus corrections. They are only available in stock lens form. Labs cannot yet grind and polish atoric surfaces.

1.0mm centers. Polycarbonate producers have always promoted the fact that only polycarbonate can be surfaced to 1.0mm center thickness. This is still true, but several companies now produce non-poly high index stock lenses with 1.0mm centers. How are they able to do this with a material that is relatively brittle when made this thin?

The answer, as DuPont used to brag, comes from "the magic of chemistry." These lens producers have developed proprietary scratch coatings that provide a cushioning effect, absorbing and dissipating impact stresses that would normally crack or break a non-poly lens. These sophisticated lenses safely pass the FDA Drop Ball test. The only down side is that this cushioned coating chemistry is not yet available for labs.

As a result, high index stock lenses with cushioned coatings are the only non-poly lenses that can be dispensed with 1.0mm centers. For surfaced lenses, poly is still the only material that can be ground that thin and pass the drop ball test.

The new 1.71. The most notable new development in the field of high index has been the recent introduction of a new alternative material that boasts the highest refractive index in plastic. This proprietary material, called Teslalid, is produced by Hoya.

Generally speaking, as the refractive index increases, the Abbe number decreases (high Abbe numbers are preferred).

The new 1.71 material has an Abbe of 36, which compares to poly's 31 and the 32 Abbe of most 1.66 index lenses. All single vision 1.71 lenses are aspheric and can be ordered for corrections ranging from +10.00D to -15.00D. The new material's specific gravity is 1.40, slightly heavier than 1.35 for 1.66 index and 1.20 for polycarbonate.

Lenses in the 1.71 material require special processing procedures. Initially, 1.71 prescription lenses could only be processed in Hoya's Connecticut laboratory, but the company now has authorized labs that can process these new lenses for them.

Stock lenses in 1.71 are also available from Hoya's authorized distributors. The company does not sell 1.71 lenses to optical chains.

PHOTOCHROMICS AND POLARIZED PRODUCT
Acknowledging the market demand for "high tech" lenses with higher refractive indices, most manufacturers include high index lenses in their lines. This includes polarized sun lenses. They are usually either 1.56 index or polycarbonate. Virtually every modern progressive design is made in some form of high index (ranging from 1.54 to 1.71 high index or polycarbonate).

In photochromics, Corning's new photochromic (Sun-Sensors�) carries a 1.56 index. Transitions had four variations available: 1.54, 1.55 and 1.56 high index and 1.59 polycarbonate.

Just this month, however, Transitions is launching its new Quantum� variable tint technology, which reports the company, gets darker faster, fades back faster, and represents a significant improvement to consistent performance at all temperatures. It was made available April 1 in poly and will be released May 1 in a 1.67 lens. The later is the Seiko 1.67 Super SV Transitions Quantum, available semi-finished with 16 base curves.

With such introductions, one wonders if the use of CR 39 lenses continue to decline, echoing the historic decline of glass? Most industry observers believe they will, but few people expect conventional plastic lenses to completely disappear. They will continue to represent an economy lens, and history has shown that there is usually a market for inexpensive lenses.

There is little doubt that chemists and lens manufacturers continue to look for "better" lens materials. In the meantime, the current variety of substrates--all with refractive indices greater than glass or CR 39--continue to jockey for market dominance. EB