February 21, 1975
The history of plastic ophthalmic lenses, not only at AO but for the industry as a whole, dates back to 1937 when methyl methacrylate (plexiglas) was first able to be molded to specific foci. The lenses weren’t really satisfactory, for they had very poor scratch resistance and also tended to soften and distort at the higher temperatures to which spectacles are often subjected.
Of particular interest at this point in time was the formation of the “Unbreakable Lens Company,” for out of this small nucleus came the talent which is responsible for much of today’s major AOLITE competition. Specifically, Armorlite, Univis, Bausch and Lomb, and Orma can all trace their beginnings back to this small Company formed in the late 1930’s. If this chart were brought up to date, I am sure many of the recent entries to the plastic lens field (Plastics Resources, as an example), could also trace their start back to the Unbreakable Lens Company.
Perhaps the most important single development in the history of plastic lenses came out of an experimental program being conducted during World War II at the Columbia Southern Chemical Company, now the Chemical Division of PPG Industries. They were involved in the quest for a plastic substitute for window glass, and formulated a series of just under 200 experimental polymers. It is the 39th of these materials which we, and the whole industry, use today as the basis for virtually all plastic ophthalmic lenses. The material, commonly referred to as CR-39 (the 39th Columbia Resin), is allyl diglycol carbonate. It has the product advantage of being thermosetting rather than thermoplastic, so will not soften and distort at elevated temperatures. It must, however, be cast rather than molded. It’s most unique property, and the one which makes it so well suited to ophthalmic application, is its scratch resistance. It is by far the most scratch resistant of the optical plastics.
Meanwhile, AO was independently involving itself with plastic lenses through the research efforts of Harry Crandon, under the leadership of Dr. Tillyer. It was during these early days that Harry developed his “Open Cell Process” which was patented by AO, and which became the basis for all AOLITE manufacturing until the early 1960’s. In fact, this process is still being used today for casting our AOLITE Aspheric cataract lenses.
In the early 1950’s AO made the decision to formally enter the cast plastic lens market by introducing a line of plano safety lenses. A new facility was constructed in our Brattleboro Plant, and in a short period of time production was running in excess of 100,000 pr./yr. of plano lenses. Meanwhile, experimental work was continuing in Southbridge to expand our capability to casting focus lenses, and by the mid-1950’s these lenses were entered into production, also at our Brattleboro Plant. Norman Laliberte, who currently works in Don Rotenberg’s organization, was foreman of that early operation.
While the Open Cell Process is well suited for casting lenses of zero power, it has some serious drawbacks when we consider focus lenses. These drawbacks caused the range of foci to be severely limited, due in part to inability of the open cell, as then constructed, to adapt to the differential shrinkages encountered in the casting process. Research has been working on ways around this problem, and in the late 1950’s came up with the addition of methyl methacrylate to form a copolymer as a way to make AOLITE material sufficiently thermoplastic to absorb the shrinkage. This made possible the extension of the foci range, and by the early 1960’s we were casting nearly 1500 different finished single vision items, covering an Rx range from +10.00 through -10.00 with cylinders through -4.00 diopters.
Meanwhile, the Southbridge Lens Development Activity was concentrating on a forthcoming new product which was to have major impact on our business -- the AOLITE Aspheric Cataract Lens. This product was introduced on an Rx basis early in 1959 and was the first plastic lens product to be produced in Southbridge; the first Southbridge AOLITE “Plant” was in what is now the Lens Conference Room, and employed a total of four people.
In the early 1960’s several things happened which required the development of a new cell concept to replace Crandon’s open cell. First, the trade was beginning to recognize the inferior scratch resistance of a copolymer product. Secondly, the market was demanding larger uncut lens sizes, but the open cell process just didn’t have the capability to make these larger size lenses. Finally, the trade was demanding plastic bifocal lenses, and these were next to impossible to produce by open cell techniques.
The need for a new cell concept was met in 1962 through the introduction of a closed cell employing a plastic gasket rather than a metal retaining ring. This wasn’t an AO invention, but was an adaptation of processes used by others in the business.
It was just about at this time that the ion exchange chemical hardening process came into being. The application of this technology to the molds used in the closed cell concept made it possible to eliminate the methyl methacrylate component from all AOLITE stock products, thereby regaining the inherent scratch resistance of pure CR-39. In making this comment, it should be pointed out that the range of foci of our finished uncut lenses was substantially reduced with the introduction of finished single vision lenses cast by the closed cell technique; this was also a factor in allowing the elimination of the methyl methacrylate component.
The first major product line to be introduced using closed cell casting techniques was the AOLITE 62mm Finished Single Vision Series. At the time this Series was designed (1962), the glass lens people had just about completed their Masterpiece I design criteria, and the decision was made to utilize this principle with the new AOLITE design. This meant flatter curves than the industry had ever seen before.
Because of the extremely large number of possible Rx combinations, the demand for bifocals in plastic was met by casting semi-finished blanks and relying on grinding and polishing to finish the Rx. Neither time nor dollars were available to allow the development of a surfacing process aimed specifically at plastic; the best that could be done was to adapt existing surfacing techniques and machinery to the plastic situation. This was done on a crash basis, and I would like to point out at this time that no major effort has ever been put into developing a first class plastic Rx processing method. As a result, our branches and customers are plagued today with problems resulting from inadequate -- in fact, virtually non-existent, plastic Rx process engineering.
The first bifocal to be brought on the market had a round segment and is in the line today as the AOLITE “D” Bifocal. The AOLITE ‘S’ 22 followed a year or two later, and the Executive came shortly after that. By the mid-1960’s our line had developed pretty much to the point where it is today, with the exception of the AOLITE 66mm Single Vision Series just recently introduced, and, of course with the exception of those products which we purchase from outside suppliers.
At this time, it would be appropriate for me to comment on a couple of respects in which our product is or has been different from much of the competition. First, I have already referred to the flatter curves employed by the AOLITE Finished Single Vision Series as a result of the design having been based on Masterpiece I criteria. A few years later when the American National Standards Institute adopted off-axis performance standards for application to plastic ophthalmic lenses, this took on more importance. Many of the AOLITE 62mm Minus Foci would not conform to these standards, and so the task was undertaken to design a new, larger size finished single vision series with off-axis performance as a paramount consideration. This effort went through many mutations, but the final result is the AOLITE 66mm Finished Single Vision Series which employs steeper curves to take advantage, optically, of the asphericity induced by our casting process. The fact that our 62mm Series had employed unusually flat curves and the 66mm Series employ unusually steep curves, makes the new Series a dramatic and somewhat startling departure from previous practice. It is still too early to know for certain just what the customer acceptance of this new, steeper curve product will be. From an optical standpoint, though, it represents a significant improvement.
One other thing which, over the years, had distinguished AOLITE products from much of the competition is the fact that their surfaces tend to accept dye more readily. This is a direct result of the way in which the process evolved, where the molds were separated from the lenses earlier in the curing cycle than is the practice with most of our competition. This is both an advantage and a disadvantage, and time doesn’t allow my going into detail here. In summary though, this procedure tended to minimize problems of premature release and mold breakage, while, at the same time, providing a lens surface which would accept a class of surface dyes with superior color stability. While the surface cure on AOLITE lenses was less than that of much of the competition, the bulk cure (representing the body of the lens) was essentially the same as the competition, and thus there was no significant difference in scratch resistance. In fact, until recently, all evidence pointed to the fact that AOLITE lenses, with their lower surface cure, were just as scratch resistant as was a product with a higher degree of surface cure. Work carried out within the past few months has shown that this is not quite so, and that surface cure does indeed have some effect on scratch resistance. The current thrust is to bring our surface cure up to a somewhat higher level than we have advocated in the past.
This brings us to where we are today. Looking back, it is interesting to list some AO firsts in the area of plastic lenses:
• AO was first to introduce minus cylinders in its plastic lens line.
• AO was first to apply the ion exchange process to plastic lens molds, thereby enabling the casting of higher power finished lenses of pure CR-39.
• AO was first to come out with plastic Aspheric lenses for low vision application - this technology led to the Aspheric Cataract product.
• AO was first to come out with Aspheric Cataract lenses.
• AO was first to introduce cast finished Rx lenses (Finished Rx Cataract).
• AO tied with Univis in the introduction of the “S” Bifocal.
• AO was first to introduce the Executive Bifocal in plastic.
• And now, AO is first to incorporate an Aspheric design in plastic finished single vision lenses.
I think this list serves to show that through the years AO has taken a position of leadership in the plastic ophthalmic lens business. It is, however, significant to note that AO chose to take a position across a broad front, with finished and semi-finished single vision lenses, bifocal blanks in a variety of different segment styles, and a line of both finished and semi-finished Aspheric Cataract products. Most of our competition, on the other hand, chose to concentrate their efforts in more limited areas. After starting out in Finished Single Vision, Armorlite effectively abandoned that area in favor of semi-finished multifocal products. Partly as a result of that specialization, they now have the lion’s share of the multifocal market. In contrast, Orma built their reputation on Finished Single Vision, and they have retained a firm foothold here.
In conclusion, it might be well to keep in the back of our minds the reasons why plastic lenses may be prescribed or purchased. As compared with glass, plastic lenses are:
• About half the weight of glass.
• Scratch resistant without special treatment (and exempt from drop ball testing by the Rx Lab).
• Adaptable to simple surface coloring techniques which result in uniform density absorptive products.
• Available in Aspheric designs, resulting in improved optical performance.
And, on the minus side, plastic lenses are:
• More easily scratched.
• A real headache for the Rx Lab to process.
1955 56mm Finished Single Vision
1957 Extended Range Finished Single Vision
1958 Low Vision Microscopic Lenses
1959 AOLITE Aspheric Cataract
1962 “D” Bifocal
1963 62mm Finished Single Vision
1964 “S” Bifocal
1965 Executive Bifocal
1972 S-25 Bifocal
1974 66mm Finished Single Vision
The influence of CR-39 (sixty years after its introduction) - 2006 article by Dick Whitney
Browse to Don Whitney Autobiography excerpt of AO
Return to AO
History Index Page