OPHTHALMIC LENSES: THEN AND NOW

Sponsored by ZEISS

By Deborah Kotob, ABOM

Learning Objectives:

Upon completion of this course you should understand:

Describe the evolution of ophthalmic lenses.
Explain the limitations of early visual aids.
List the key milestones in progressive lens design and technology.

Course Description

This course takes us back in time to early lenses, before and after the advent of eyeglasses. We will learn about the merging of lens manufacturing and optical science in 1912, with the first science-based lens design, Punktal from ZEISS. Continuing through the years, we will end with a brief overview of the latest ophthalmic lens breakthroughs and the future of vision science.

Credit Statement

This course is approved for one 1 hour O.D. CE credit by NYSSO

Support

THIS COURSE IS SUPPORTED BY AN EDUCATIONAL GRANT FROM ZEISS

The early days: Imagine life for ametropes in a world without ophthalmic lenses and eyeglasses. Those with a refractive error managed life with either poor distance or poor near vision, or both. Those fortunate enough to be emmetropes and free of refractive errors were helpless to stop near vision decline after 35 to 40 years of age. Imagine the effect of this decline in vision for artists, scientists, mathematicians and other skilled craftspersons of the day.

The invention of glasses is heralded as one of the 10 most significant inventions in human history after the wheel and fire. But when and where did the invention of a proper visual aid begin?

The father of optical theory – The world’s first vision aid: The Arab scholar, mathematician and astronomer Ibn al-Haytham known in the west as Alhazen (ca. 965-1040 CE) was the first to suggest that smoothed glass might assist someone suffering from a visual impairment. It was many years later when the 1912 Latin translation of his Book of Optics, found an attentive readership in monastic communities. Thirteenth century Italian monks developed a semi-spherical lens made of rock crystal and quartz that when placed on a piece of writing, magnified the letters! This “reading stone” (Fig. 2) was a true blessing for older monks suffering from presbyopia and significantly improved their quality of life.

While reading stones are the forerunners of present-day eyeglass lenses, the origins of the first spectacles or eyeglasses with two lenses remain a mystery. However, there is evidence that early eyeglass production originated around 1300 in Venice, Italy, a renowned center of glass-making at the time. From here, eyeglass production gradually spread to other countries. These early eyeglasses were sold by traveling merchants who purchased a large number of eyeglasses from the manufacturers and then resold them along with other wares. The lenses in these eyeglasses were generally of poor quality, often produced by unskilled workers. The purchaser tried on many eyeglasses and selected the pair they felt worked best. In the 15th century, the invention of the printing press fueled demand for eyeglasses and mass-production methods to produce inexpensive eyeglasses for the new reading public.

The glasses we see and wear today ultimately emerged at the beginning of the 18th Century. Early visual aids either slid down the wearer’s nose until the introduction of “ear glasses” or “temple glasses” that featured a bridge and temples to hold the glasses in place on the nose and the ear. A metal ring at the end of the temple kept the glasses from sliding forward when the head was bent to read or write. The first examples of these glasses appeared in London and can be seen in a promotional brochure from the English optician Scarlett from 1728. In 1784, Benjamin Franklin is credited with creating bifocal lenses, the first instance of distance and near correction in the same pair of glasses.

The 19th Century saw a turning point in the eyeglass sector. In the 1800s, most glasses were sold in hardware stores until jewelers gradually took over the dispensing of spectacles. Methods for determining an eyeglass prescription didn’t yet exist, so people would try on one after another until they found a pair that worked for them. In the 1800s, the first eye exams for glasses used a “trier“ tool with lenses of different focal lengths placed in front of a person’s eyes. The number of trial lenses in this tool were limited, and the purchaser had to choose from which worked best. Trial lenses became standardized in 1875 when the diopter was adopted as a unit of measurement. In 1862, Dutch ophthalmologist Herman Snellen invented the standardized eye chart that is still in use today. In June 1800, Prussia’s King Frederick William III granted permission to set up a factory for visual devices in Rathenow to Johann Heinrich August Dunker and Samuel Christoph. Duncker’s invention of the 11-spindle mechanical grinding machine (Fig. 3) produced more precise eyeglass lenses faster. In 1801, Duncker sold his products through dealers at fixed retail prices, which proved to be a highly successful business model. Following Duncker’s model, other eyeglass factories soon emerged.

THE 20TH CENTURY

The founding of Carl Zeiss Eyeglass Division: Eyeglass lenses were produced at Carl Zeiss under the direction of Moritz von Rohr and young mathematician Hans Boegehold from 1908. Production was initially limited to prototypes for practical testing of calculations. With the introduction of Punktal lenses, the time had come for the creation of an independent eyeglass division within the larger Carl Zeiss enterprise. The “Opto” department—the internal abbreviation used for the eyeglass production area at Carl Zeiss—was set up on April 1, 1912. The scientific director was Otto Henker, who later became well known as a university professor and cofounder of the Jena School of Opticians.

At first glance, the establishment of an eyeglass division under the roof of Carl Zeiss did not seem to be anything special. Similar factories had sprung up all over Germany throughout the 19th century. The difference centered around the powers in Jena deciding against the established business model, which employed large numbers of unskilled workers earning low wages. For the very first time, the production of eyeglass lenses was to be aligned with the standards of optical instrument construction. Carl Zeiss redefined the eyeglass lens as an advanced optical device not only from the design point of view but also in terms of its production.

Unlike traditional handcrafted products such as microscopes or binoculars, the planned quantities for ZEISS eyeglass lenses quickly reached mass production levels. Around 120,000 lenses were delivered in the first half of the fiscal year 1913 alone. Time and cost optimization were therefore paramount in both production and logistics. The swift achievement of these high volume production milestones fueled the invention of many new innovations and technologies.

The first opticians’ school: The Grand Ducal State School of Opticians was formally established in Jena. The founders, von Rohr, Henker and Pistor, published numerous textbooks for ophthalmic opticians in the following years. One of the most famous is the Introduction to the Theory of Spectacles, published by Henker and Pistor in 1921, which was subsequently translated into English, Spanish and French. The “ophthalmic optician” profession came into being in Germany in the late 1920s and is inextricably linked to greatly improved and standardized training. Hermann Pistor headed the first opticians’ school in Jena until 1951. It was never compelled to close even during the war years from 1939 to 1945 and continues to this very day under the name of its first director, Pistor. Pistor endeavored to provide students with expert training while emphasizing the rich and important history of ophthalmic optics. “The young optician will not feel at home in his new profession until he also knows its history,” says Pistor in the foreword to the German version of his Introduction to the Theory of Spectacles. As early as 1911, the Central Union of retail opticians and the French oculists’ union drafted regulations, adding to the law of 1892 on the sale of optical products, and they set the requirements to obtain the title of optician. The sale of eyeglasses evolved from traveling merchants to hardware stores, to jewelers to trained opticians in optical retail locations.

The first lenses with point-focal imaging: In 1912, Moritz von Rohr calculated pointfocal imaging eyeglass lenses, which were marketed under the name PUNKTAL. They were the first axially-symmetric eyeglass lenses to minimize the blurring that occurs when looking through the edge areas of a lens. This revolutionary achievement is still shaping the world of eyecare today.

In 1932, ZEISS created the first modern pair of eyeglass frames named Perivist. They became the world’s first frames fitted to accommodate the wearer without sliding down. Otto Kunze was not merely copying or modifying existing frames, he patented a wholly new design around 1932. An innovative feature of the new frames was anatomically contoured temples attached to the uppermost area of the frame for unhindered lateral vision. The flatter top combined with an oval-shaped bottom prevented the lenses from rotating in the frame as it was prone to in the round frames that were standard in the 1920s and 1930s. Even the best-quality lens is of little benefit if the eyeglasses and lenses in front of the wearer’s eyes do not remain steady. Because the lenses were oval at the bottom and flattened at the top, the shape was given the name of “pantoscopic.” This resulted in a relatively large field of view without the risk of the lenses becoming dirty due to contact with the eyebrows. In addition, the frame was fitted with two flexible nosepads, which ensured a better fit than the eyeglass bridge of the time. The comfortable and yet precise fit of the eyeglasses was received so well by wearers that this system soon became standard. A little bit of Perivist remains in many pairs of eyeglasses to this very day.

The first progressive lens design: “Although progressive addition lenses (or ‘PALs’) didn’t enjoy commercial success until the 1960s, the concept has been around since Owen Aves, cofounder of London’s Institute of Optometry, patented a progressive lens design in 1907. Because of the dual-surface nature of this lens design, it was limited to spherical prescriptions. Shortly after, Henry Gowlland patented improved progressive lens designs in 1909 and 1914, which utilized a conicoidal back surface to produce the addition power. Estelle Glancy at American Optical patented one of the earliest progressive lens designs that relied exclusively on a single progressive front surface in 1923. However, early lens designs generally proved impractical to produce in prescription form in mass quantity with the technology available at the time. The first commercially successful progressive lens in Europe, Essel’s Varilux lens, was introduced in 1959. The Univis Omnifocal, introduced in 1965, became the first commercially successful lens in the United States. The success of these lenses was due in no small part to technical achievements in fabricating asymmetric surfaces on a large-scale production basis, often relying on clever grinding assemblies. Since the 1960s, progressive lens usage has increased rapidly as the designs continued to improve.” –Daryl Meister (opticampus.opti.vision).

For ZEISS, Gradal HS progressive lens design became the primary sales driver for the Carl Zeiss eyeglass operation. People were clearly willing to spend more money on eyeglasses that allowed them to see at all distances—especially those in industrialized nations. The move toward progressive lenses enabled Carl Zeiss to unleash its full range of skills and expertise. The surfaces of progressive lenses, which look like a landscape of mountains and valleys when magnified, represented far greater mathematical challenges than even the most complex single vision lenses. Without computers, this new development would have been virtually impossible. The lenses were calculated using the mathematical “spline” technique, which is also used to approximate the aerodynamic characteristics of aircraft wings. Equally challenging was the task of producing such complex lens surfaces with their many thousands of coordinate points. ZEISS progressive lenses were at least in part based on technology transferred from the aerospace industry. Drawing on the experience acquired by its astronomy department during the preparation of the German ROSAT satellite survey mission, in which researchers had developed high-precision mirrors for the X-ray telescope onboard the satellite.

With the company’s in-depth understanding of human vision, the goal of researchers was to minimize any impairment of the interaction of the two eyes when looking at close-up objects. This is especially hard to achieve with progressive lenses because our eyes converge inwards when we change our focus from far to near objects. However, the power of eyeglass lenses deflects the wearer’s line of vision in this situation—outwards in the case of plus lenses and inwards in minus lenses. This in itself would not necessarily be a problem since we can compensate to some degree for this difference. However, due to their symmetrical design, the first progressives had the drawback that the wearer experienced different levels of visual clarity and ray deflection for their left and right eyes. In the early 1980s, Gerhard Furter, a mathematician employed by Carl Zeiss, created a new design that virtually eliminated this problem. Hans Lahres, a developer who worked with Furter, explains: “Gerhard Furter understood that we had to achieve equally sharp images of objects for both eyes in all lines of vision and the same lowering of the eyes for near vision. We described these conditions as horizontal symmetry. And by carefully structuring the progressive surface to take into account all the different optical powers, we achieved our goal.” The fact that the new Gradal HS design offered practical benefits in addition to its theoretical advantages was demonstrated by its huge commercial success.

The increasingly fast computers and highprecision CNC machines that became available at the beginning of the 1990s made the production of customized progressive lenses feasible. However, this was only the beginning of the actual challenge, as Erich Hofmann, a mathematician for Carl Zeiss Eyeglass Lenses from 1981 to now, remembers: “We had to find an algorithm that would function independently for any ordered values with practically no assistance. Developer Helmut Wietschorke, named in several Carl Zeiss patents, succeeded in achieving this in a truly magnificent way. A further difficulty consisted in producing the front side of the lenses individually as a freeform surface. Together with the company Schneider from the German town of Fronhausen, we developed a machine that with the aid of a diamond stylus and a magnetically mounted drive, machined the rapidly rotating plastic blanks with an accuracy of just one-thousandth of a millimeter. Each surface was defined by around 40,000 points. In the beginning, I could hardly believe the speed and precision with which the approximately 12-kilo tool platform oscillated with constantly varied frequencies.”

Early outdoor sun protection: In 1876, American Optical expanded from ophthalmic eyeglasses to sunglasses. In 1913, they obtained the rights to Sir William Crookes’ invention of UV-absorbing protective dyes in lenses. During World War II, AO developed mobile units with frames, lenses, machinery and refraction equipment to allow qualified personnel in the field to conduct eye exams and fit troops with ophthalmic eyeglasses and sunglasses. The popularity of leisure sports, motorcycles and automobiles, and a rise in health awareness sparked the demand for sun protection eyewear in the 1920s. With Umbral, the Opto department launched its first eyeglasses for use by anyone and everyone—with or without an optical power. Compared to many competitive products, a special feature of the lenses was the even distribution of the tint across the entire surface of lenses featuring a corrective power. As these lenses generally display differences in thickness between the edges and the center, this would not have been possible if the entire glass melt had been tinted. The secret lies in applying a uniform layer of colored glass to the clear plus or minus base lens. Carl Zeiss purchased the gray-brown tinted base material exclusively from the SCHOTT factory in the town of Mitterteich. In 1929, Foster Grant sold their first pair of sunglasses on the Atlantic City, N.J., boardwalk.

For people who enjoyed spending time outdoors, the ZEISS Opto department developed special sport sunglasses lenses. With a metal frame, leather padding and a leather strap, these sport glasses fitted snugly against the contours of the face and therefore protected against wind, sun and rain.

This marked the development of eyeglasses to fit specific lifestyles.

Better vision without reflections: ZEISS received the first patent for anti-reflective coating technology. Lens reflections, both on the surface and internally, significantly reduced visible light transmission to the eye and were cosmetically unattractive, obscuring the wearer’s eyes in the reflected glare. Although the discovery of anti-reflective coating was in 1935, by physicist Alexander Smakula, the first patent wasn’t published right away because it was a military secret. Smakula developed the first anti-reflective coating using the theory of wave interference to cancel reflections and increase visible light transmission through the lens. His original application was for military use to reduce reflections from aerial lenses, riflescopes and submarine periscopes. His innovation made them both more difficult to spot in combat and improved their visible light transmission for better optics. The coating technology for ophthalmic lenses referred to as ET coating but it did not debut on glass lenses until 1959 and on plastic lenses in the 1970s. The benefits of the ET coating became obvious after the market launch in 1959. The coated lens provided the wearer with greater visual clarity and accentuated his or her eyes more by removing distracting reflections from the front of the lens more effectively than before. Eyeglasses quickly became aesthetically more attractive, a benefit not lost on the wearers. They also significantly improved night vision, a real boon for night driving. The coatings used by ZEISS today consist of multilayered stacks of varying indices that reduce reflections almost across the entire spectrum of visible light for maximum visible light transmission (VLT) and a virtually reflection-free lens.

THE 21ST CENTURY – PIONEERING BETTER VISION

At the beginning of 2007, one subject dominated discussions between eyecare professionals and major lens manufacturers more than any other: a new method of refraction presented by Carl Zeiss and other manufacturers based on wavefront technology. For a long time, the understanding had been that eyeglasses could never perfectly correct aberrations of the moving eye. Higher-order aberrations in particular, “coma” or “spherical aberration” seemed to be unavoidable evils. The wearer was unaware, as these aberrations are of practically no significance in standard subjective refraction. However, they do influence the perception of contrast and color intensity and night vision in which the pupil of the eye dilates. In the worst-case scenario, these aberrations can also impair the overall quality of the wearer’s vision. Wavefront analysis originated in ophthalmology and involved the projection of a pencil of light onto the retina. The system used the resulting reflection to calculate the aberrations of the eye. For the first time, graphic measuring diagrams also clearly illustrated to the layperson that no two eyes are identical. Patients who had previously been unsatisfied with their glasses despite the many efforts of their eyecare professionals now said that they enjoyed a significant enhancement of their vision. They highlighted improvements in both visual acuity and night vision. In the view of the vision care business group experts, this was the best possible proof that their method did work. The new method provided the eyecare professional with an additional tool. Refraction with a trial frame and optotypes remained essential requirements.

THE FUTURE OF VISION - NEUROSCIENCE

Another field of optical research is centered on achieving an understanding of how images are processed in the brain. As Bernhard Wittmann, head of development in Aalen, explains: “Current knowledge in the field of the neurosciences will definitely have an impact on ophthalmic optics in the future. In Japan, for instance, the initial experience is being gained in refraction with the aid of brain wave measurement.” Whittmann imagines a future where the field of the neurosciences facilitates further optimization of individualized designs.

In summary: Almost inconceivable as little as 20 years ago, lenses today are now able to address the unique vision challenges of our modern times. These include frequent use of digital devices, both when we are stationary at our desks or staring at our smartphones while on the move. Furthermore, lenses are no longer limited to refractive error correction. Lenses are under development which have been shown to slow the progression of myopia by addressing the lens’ peripheral power to stop or slow the eye elongation and subsequent complications. There are also lenses that enhance color vision and even some that help those with color deficiencies experience colors they have never seen before. There are lenses for better binocular fusion. There are everimproving intelligent lens materials that dynamically change color when exposed to UV light. Today we have coatings that make lenses more durable with nano-particle reinforced hard coatings and optimized adhesive layers, and easy-to-clean AR coatings with built-in UVA protection.

Innovations in lens science are certainly impressive, and they continue to advance at an accelerating pace in the digital age. The earliest lens advancements were slow to be adopted, often taking decades or even centuries to enter the mainstream. Today, with rapidly expanding optical knowledge and industrial technology evolving so quickly, new lens innovations are being uncovered at breakneck speed. Who can tell what advancements await just around the corner? One thing is for sure, the eyes of our current generation are likely to experience more breakthroughs and improvements than at any other time in history.

The primary resource for the information contained in this course is Better Vision, Carl Zeiss Eyeglass Lenses 1912 – 2012, published by the Carl Zeiss Archives, author: Stephan Paetrow.