Spectacles: Past, present, and future

SURVEY OF OPHTHALMOLOGY

VOLUME 30.

PERSPECTIVES

NUMBER 5. MARCH-APRIL

1986

IN REFRACTION

MELVIN L. RUBIN, EDITOR

Spectacles: MELVIN

L. RUBIN,

Past, Present, and Future M.D.

Department of Ophthal~olo~,

Uniuersit)i

ofFlorida,

Gainescille, Florida

Abstract. The history

of spectacles is reviewed with particular attention to recent developments in lens materials. The author advocates the use of polycarbonate, a high resin plastic, because of its strength, high refractive index, light weight, and resistance to fogging. (Surv Ophthalmol 30:321-327, 1986)

Key words.

CR-39

l

history

of spectacles

l

A pair of spectacles, that distinctive combination of two lenses set into a device that holds them in front of the eyes, has proven to be one of the most useful appliances known to civilized man. Its importance can be gleaned from one statistic: Almost !4 of the American populace are eyeglass wearers, and this comprises an optical market of about 7 billion 1986 dollars. In addition to the benefits spectacles offer to readers and writers, spectacles can provide clear and comfortable vision for those performing all kinds of tasks - mechanical, technical, and artistic. They come in a bewildering variety of forms. A list of developmental designs includes riveted spectacles, pince-nez, wire rims, spectacles with side bars, spectacles with curved eyepieces and spectacles of wood, leather, fishbone, horn, acetate, wire, or precious metals. Lenses may be extremely large and call attention to themselves, or so small as to minimize their presence as much as possible. Although they comprise such an important part of our daily lives, the fact is we all take our glasses for granted. Nevertheless, it behooves us to learn something of their past and how they evolved. To this end, I will present a short history of frames and lenses, fol-

lens

l

polycarbonate

l

spectacles

lowed by a look at hard resin (plastic) corrective lenses now in use, and my views on a new type of plastic lens that offers significant advantages.

History PRE-SPECTACLE

VISUAL

AIDS

We know that no visual instruments existed at the time of the ancient Egyptians, Greeks or Romans. That fact is supported by a letter written by a prominent Roman about 100 B.C. in which he stressed his resignation to old age and his complaint that he could no longer read for himself, having instead to rely on his slaves. The Greeks were known to have used a glass ball filled with water for magnifying purposes. One hundred-fifty years later, Nero used an emerald held up to his eye while he watched the gladiators fight. That, however, is not proof that the Romans had any idea about lenses, since it is likely that fiddler Nero used the emerald merely because of its green color, which filtered the strong sunlight. (Or, perhaps Nero used his emerald as a mirror to detect subversive activity behind him!) 321

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The Chinese are deservedly credited with many early scientific developments that were later adopted by Europeans, and some give them credit for developing spectacles about 2000 years ago - but, they used them only to protect their eyes (and themselves) from an imaginary evil force! And, like Nero, they also used colored lenses for protection against bright light. They did not develop lenses to aid vision. Interestingly, in the 15th to 17th centuries, artists painted biblical personalities with spectacles. They did so not because they thought that spectacles existed in biblical times, but simply because it was their custom to paint their subjects surrounded with accessories that were currently fashionable. (If we were to find such anachronisms on TV or in movies, we would call them “technical errors!“) Around 1000 A.D., the reading stone - what we now know as a magnifying glass - was developed. What it was, was a segment of a glass sphere that could be laid against reading material to magnify the letters. It enabled presbyopic monks to read and was probably the first visual aid. (Songwriters in the middle ages thought it was so novel they even composed songs about it.) The Venetians learned how to produce glass* for reading stones, and later they constructed lenses that could be held in a frame in front of the eyes instead of directly on the reading material. DEVELOPMENT

OF SPECTACLE

DESIGN

The first true spectacles were made about 1300. They were constructed with the two convex lenses surrounded by a thick ring of oakwood or horn, with a rivet pivot over the nose and a handle at the side. They were used only to correct presbyopia. (The other refractive errors had not yet been recognized). Spectacles for presbyopia were regarded as extremely valuable optical instruments. Their first use was in the high court of Venice, and for centuries thereafter, they were worn only by monks, scholars, and members of the rich and privileged classes. Leather was the material most commonly used for the frames, but even 200 years later, riveted spectacles were still pivoting over the bridge of the nose, suggesting that the trade of spectacle design was inordinately slow to develop. The early spectacles had to be held by hand. Later, a headband was added. Further along, during the 16OOs, came the pince-nez, with a bridge that sprung closed on the nose. During the 1700s the monocle was developed by a German, Baron von *Later, in 1675, the first completely clear glass was made by Ravenscroft, a London glassmaker, who added flint to the glass, and thus produced crystal (or crystalline) glass.

RUBIN Stoch (1691-1757). it was usually attached to the wearer with a string, since the lens had to be held by the individual’s orbicularis muscle and thus was frequently dropped. The first monocle wearers were men in society’s upper classes, which may account for the aura of arrogance the monocle seemed to confer on the wearer. Women began wearing the monocle in the early 1900s. Their lenses were combined with elaborate frames that were usually set with precious stones. After World War I, the monocle fell into disrepute, its demise hastened no doubt, by its association with the German military. The lorgnette - two lenses in a frame the user held with a lateral handle - was another 18th century development (by Englishman, George Adams.) The frame and handle were frequently artistically embellished, since they were used mostly by women and more often as a piece ofjewelry than as a visual aid. In spite of the handle, they were worn on a string or chain around the neck, making them conveniently available. True spectacles as we now know them probably stemmed from England during the period from 1700 to 1900. The first design, like our present eyewear, consisted oflenses held at a fixed distance from each other, in a frame with a bridge that rested on the nose, and temple pieces attached by joints. The second design, called glass spectacles or rimless glasses, had a bridge fastened directly to the glass by holes drilled into the lenses. For all its developmental changes over the years, the spectacle frame is one of technology’s best examples of poor engineering design. It virtually teems with defects. The center of gravity and center of rotation are too far forward to keep the lenses in optimal position. Frames depend far too much upon noses, which vary in size, shape and firmness, and upon ears, which vary in symmetry, in contour of cartilagenous support, and in the amount of hair interposed between frame and ear. They require that the lens plane be perpendicular to the visual axis, yet this is geometrically possible for only one direction of gaze - all other directions will induce changes in spherical and cylindrical power. They require that the optical center of each lens be supported directly in front of the center of each pupil, but this is manifestly impossible since the eyes are constantly moving, altering in version and vergence. Moreover, the frames are constantly sliding down the nose, and this further alters alignment. Glasses should be comfortable to wear, yet they are often too heavy. They must conform to esthetic needs, but the constant vagaries of high fashion usually equate esthetics with larger and larger frames, and this means still greater weight. Obviously, as an engineering solution to the problem of design, cur-

SPECTACLES:

PAST,

PRESENT,

323

FUTURE

Fig. 1. Chinese spectacles and Shagrin case, c. 1368-1421 (Courtesy of the Foundation Museum of Ophthalmol-

Fig. 2. Scissors glasses, French, c. 1750 (Courtesy Foundation Museum of Ophthalmology).

of the

%Y).

Fig. 3. English spectacles, 1795 (Courtesy tion Museum of Ophthalmology).

Fig. 5. Victoria the Foundation

lorgnette, Museum

of the Founda-

American, 1880 (Courtesy of Ophthalmology).

Fig. 1. Spectacles with sliding lenses, c. 1810-1830.

temples

and colored

folding

of

Fig. 6. Pince-nez, American, c. 1880 (Courtesy Foundation Museum of Ophthalmology).

of the

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rent spectacle frames leave much to be desired. But, despite their numerous shortcomings, the great majority of those who have to wear spectacles are surprisingly comfortable. Perhaps this is only a subconscious reflection of their gratitude for the miracle of improved sight. At any rate, high patient motivation certainly simplified the dispenser’s seemingly impossible task, which includes, in addition to satisfying optical needs, adjusting each frame to the whims of anatomy of each individual patient so that it performs its function adequately and in acceptably good taste. So far, I have been emphasizing the development of frames rather than lenses. The latter’s history should be mentioned too. DEVELOPMENT

OF LENSES

The ancient Egyptians and Greeks did know about the laws of reflection, but they were not aware of refraction, and thus knew nothing about lenses. About 100 A.D., Ptolemy was the first to write on elementary optics, but it was not until a century later that Alhazen, an Arabian astronomer, formulated theories about the refraction of light. He was the first to point out the possibility that the eye could be helped by using an appropriately cut optical lens. But he missed his opportunity by not following through with any practical conclusion from his theoretical deliberations. In 1250, Roger Bacon he proved, theoalso “dropped the ball.” Though retically, that visually defective individuals could be made to see small letters through ground lenses, he did not put his theory into practice. (It was not until about 1600 that Snell actually deiined the laws of refraction.) The spectacles that evolved from “the reading stone,” then, to aid near vision were designed only to correct presbyopia. The first known use of spectacles to correct myopia was in about 1500, but it took still another 200 years for myopia correction to become routine. [The monocle was the style at that time, and when it was used for distance viewing (tele-scopy) of an object, it was called a “telescope.“] There was still no science of refraction, so the scientific correction of refractive error was not possible until much later, in the late 18OOs, when it could at last be measured. During the 1400s and early 15OOs, spectacle makers bought the raw materials for making glass directly from foundries and made the glass as well as the ground, finished lenses. Later in the 15OOs, lensmaking became separated from glassmaking: the glass was prepared in special shops, and the lenses were ground in prisons or in workhouses. Spectacle makers mounted the lenses in frames and sold them to peddlers, who were the primary distributors, though the practice of spectacle peddling was pro-

RUBIN hibited in any area where there was a local spectacle maker. (Protectionism apparently existed a long time ago!) Spectacles eventually became mass-produced, lowering costs, but also discouraging spectacle-making by those who were truly skilled. The result was that the overall quality of spectacles suffered . By 1850, there were 7% million pairs of optically defective spectacles glutting the market, which drove a Prussian priest named Duncker to start a company that utilized precise industrial production processes. Similar plants were started by Voigtlander, an optician, in 1815, and by Rodenstock in 1877. Both these companies, still famous names in optics, initiated quality lens production processes and, in the late 18OOs, they insisted that their lenses be fitted using special procedures based on what was then scientific optics. Complementing them later, at the turn of the century, was the Zeiss company. The historical development of the measurement of refractive error included the important names of Purkinje (catoptric images, 1823), Helmholtz (ophthalmometer, 1864), Cuignet (retinoscope, 18731, and Gullstrand (photokeratoscope and slit lamp, as well as the basic optics of the eye, 1896). Gullstrand was an ophthalmologist who later won the Nobel prize. Moritz von Rohr was another important scientist whose work helped establish the basis of modern spectacle lenses. The development of optical glass and the design of the proper lens shape to minimize aberrations for optimum performance for a given power were elaborated and refined in stages over the last hundred years.

Hard-resin Lenses Instead ofenumerating all the currently available lens products, which would include one of my favorite topics - high index glass for a cosmetically acceptable high-minus spectacle I would rather review two types of plastic lenses: the hard resin lens, which was developed in the 193Os, and the polycarbonate lens, which was developed in the 1970s and is now revolutionizing the optical industry. Somehow, there has been an underwhelming acceptance of plastic spectacle lenses by a dubious public and by their refractionists. Perhaps there is too much negative connotation to the word “plastic,” which generates feelings of optical inferiority and softness (that is, easy scratchability). In 1978, only 40% of all spectacle lenses were made of plastic; in 1984, 60% were. Although plastic has been making inroads, there is no good reason why that figure is not closer to 90%. Plastic lenses have many

SPECTACLES:

PAST, PRESENT,

FUTURE

advantages over glass, but few refractionists know much about them or how they have developed and improved CR-39 Clear plastic was first used in airplanes for cockpit canopies to protect pilots from the windstream; for obvious reasons it had to be transparent and distortion-free. In the United States, this plastic was called Plexiglas, or lucite. The material, a polymethylmethacrylate, was gradually relined for making plastic spectacle lenses, and in 1937 the first plastic lenses were manufactured and distributed. After marked improvements, the new plastic was called Armorlite. Pittsburgh Plate Glass Company further relined the material, which they called CR-39 (Columbia Laboratory Resin, 39th in the series of research products.) Ralph Drew, in his suberb book Professional Ophthalmic Dispensing, compares the manufacturing of CR-39 lenses to baking bread. “Begin with a gooey dough (CR-39 monomer); add yeast (a catalyst, which is isopropyl procarbonate, IPP), and any ingredient you think might improve it (a co-polymer). While the dough is still in plastic form, pour it into a baking tin (mold) to give it the finished shape you want; then put the formed loaf into an oven and bake (to polymerize it). Finally, remove the bread from the mold and you have a thermoset loaf.” Clearly, the finished CR-39 is not really plastic (that is, pliable), though the original viscous monomer is indeed liquid and thus, more appropriately called “plastic.” The polymerized lens has no plasticity at all. It is quite rigid, so any shape or power modification must come from cutting or grinding. The truth is. a plastic lens is no more “plastic” than is a glass lens, nor is it any more synthetic. Both are man-made, both were liquid at one stage in their manufacture, and both congealed and soliditied after cooling. As a matter of fact, a piece of solid glass is more “plastic,” since, when heated again, it can be blown into a different shape, a feat that cannot be accomplished with a piece of cured CR-39. The greatest advantage of CR-39 is that it protects the patient better than glass, and if the plastic material does break, the fragments are larger, blunter, and fly off at lower velocity, thus being considerably less dangerous than glass. Moreover, CR-39 has more resistance to pitting by rapidly flying particles than glass. POLYCARBONATE

LENSES

Now we have a new, space-age plastic - polycarbonate. Developed in the 1970s for Air Force flight helmets and visors, polycarbonate has a number of inherent advantages over hard resin CR-39, but it

required some new technologies before commercial applications could begin. The necessary technologies have now been developed: 1) injection molding ofsufficient quality to permit consistent lens and bifocal surfaces, and 2) comparable hard coatings to protect those surfaces. Polycarbonate is an almost magical material. It is “metal” because of its excalled a thermo-plastic tremely high impact strength - even greater than that of aluminum. As strong as CR-39 is, polycarbonate can withstand over five times the impact energy. Let’s look more closely at polycarbonate’s extraordinary strength. The FDA requires that all eyeglasses be capable of withstanding l/x foot-pound of energy without shattering. (That is not much of a safety requirement, since most people are routinely exposed to more than this.) An apple tossed 20 feet, for example, generates about 2% foot-pounds of impact energy, which is sufficient to easily break glass and even CR-39. Polycarbonate, on the other hand, will resist fracture after being hit with a high-speed hockey puck, or for that matter, with a hammer. Its impact resistance is about 20 foot-pounds, which makes it unquestionably safer than any other standard spectacle material. Early on, polycarbonate was not useful for lenses since its relatively soft surface was too sensitive to abrasion. Now, excellent abrasion-resistant coatings alleviate the problem. Other advantageous properties over glass and CR-39 include the following: Polycarbonate has a low specific gravity (weight per unit volume) of 1.20, compared to that of hard resin, 1.31, and crown glass, 2.53. Polycarbonate has a high reflcctive index (1.586) compared to crown glass ( 1.523) and CR-39 (1.498). Because of these two factors, for comparable lens sizes and powers, the edge thickness and overall weight of the polycarbonate lens is significantly less than either glass or CR-39. Look at the difference in edge thickness for the three materials. [The front basecurves, center thickness, and lens diameters are held constant (and are thus comparable) for each material. 1 For a - 8 D lens, the edge thickness of the CR-39 is ‘/Lmm greater than glass, while that of polycarbonate is one full millimeter thinner than glass and 1’5’~mm thinner than CR-39. Thus. for high myopes, who find the thick CR-39 lenses unacceptable cosmetically, there is an excellent alternative, which permits their corrective lens to be much thinner, more like one made of high-index glass, yet lighter in weight. Clearly, polycarhonate has a remarkable constellation of advantage over both CR-39 and glass. U’hat about bifocals? All plastic lenses (that is, both CR-39 and polycarbonate) have the bifocal segments made in the one-piece format. Only with

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glass is a fused segment available. To date, progressive-addition lenses (the so-called “seamless” multifocals) have not been made in polycarbonate, but, within a few years, even that product is likely to be produced. And what about cost? Crown glass and CR-39 lenses retail for about $30 per single-vision pair; in polycarbonate, approximately $40. For bifocals in glass, the cost is about $60; in CR-39 about $70; and in polycarbonate, about $90. So, overall, polycarbonates are about 25% more expensive than CR-39. But considering the advantages, that cost differential is not inordinate. Other benefits not previously touched on are the following: Polycarbonate is a much better ultraviolet absorber than CR-39 or glass, and therefore, a better “protector.” Also, when combined with its usual abrasion-resistant coating, polycarbonate is resistant to most chemicals found in industrial or home settings still another safety feature. Any type of plastic is far more resistant to fogging than glass. If you are wearing glass lenses when you move from cold air into a warm room, the glass, because of its high thermal conductivity (approximately live times as much as CR-39), withdraws the heat rapidly from the air in contact with it. Thus, the air reaches its dew point and deposits a wet mist on the glasses. With any plastic lens the heat conduction is far slower too slow to cause much condensation of the air’s moisture, hence less fogging. On the minus side, polycarbonate, even with coating, is not as hard as glass; yet because of its other advantages, I feel it qualifies for the slight extra care that is necessary to protect the surfaces. You should prescribe these lenses to responsible patients to whom the proper care can be explained. They need to know that, to clean a lens, it should be moistened first and then wiped slowly and gently with a soft cloth. The lenses should be stored in a lined case that should be the type that glasses can be placed into, not slid into. If cared for in this way, the lenses will last indefinitely. Another of the less favorable characteristics is the tendency of plastic to warp when there is irregular pressure applied by the frame. The solution is not to avoid dispensing plastic, but to use fastidious technique in lens edging and frame insertion. Regarding lens tints, almost any color can be satisfactorily coated onto plastic lens surfaces. The colors are fast, and no matter what the lens thickness due to power variation, the tint density will be uniform. You might ask if there is anything wrong with polycarbonate. The answer is, not very much! The only real disadvantage to date involves its manufac-

RUBIN turing process, since the quality control of the lens surfaces is still not as high as it is with CR-39 or glass. But progress is being made. Optical Radiation, Inc. is currently developing a new molding technique that uses computers to generate the surface curves. Whether or not their process turns out to be best or leads to yet other processes that further improve this material, the fact is, even now, polycarbonate is extremely worthwhile and should be strongly considered for your lens prescriptions. (In view of my “strong sell” for polycarbonates, I state publicly that I have no commercial interest in this product.) Who, then, should wear plastic lenses? My own answer is, essentially everyone. Their safety, light weight, low tendency for fog, and their resistance to pitting make plastic lenses ideal. But please, do not view them as a substitute for glass. That attitude tends to idealize glass and place it on a pedestal, and makes plastic a second-class citizen. The facts point to the contrary: plastic lenses should be admired for what they are - a superb advancement in optical technology. Currently, only 2% of lenses being prescribed are polycarbonate. The low market share occurs primarily because refractionists are generally unaware of its availability or are reticent to prescribe it. Perhaps they have been burned by the quality control. But, the situation is rapidly improving. My own prediction is that polycarbonate will, over the next decade, replace glass and CR-39 as the ophthalmic lens material. As I stated earlier, there is no reason why 90% of all lens prescriptions should not eventually be fabricated out of this space-age material. Obviously, the more that practitioners learn about it, the more competent and effective they will be at dispensing it.

Conclusion I doubt if any of us can imagine what our life would be like without spectacles. Those of us who have refractive errors or are presbyopic would otherwise miss so many joys of this world, and our spiritual and physical capabilities would be considerably reduced. Fortunately, with few exceptions, we can correct essentially any refractive error, and frames can be varied and tailor-made to fit the needs and wishes of any individual. The chronological development of spectacles, originating from the reading stone was a long one. It was both aided and retarded by social conditions, style, quality of available materials, and technology. The current influence of the mass media has helped establish our modern view: spectacles are not an unslightly crutch, but can be comfortable and create a distinctive fashion style. Further developments

SPECTACLES:

PAST, PRESENT,

and designs will assuredly continue to evolve For a long time, refractive errors could be corrected only with spectacles, but now there are a number of other possibilities: contact lenses, intraocular lenses, and various forms of refractive keratoplasty. These new methods may perform the same job as well as, or sometimes even better than, spectacles. Yet, the spectacIe, becausr of its simplicity, should continue to form the mainstay of refractive error correction far into the future. As new, stronger, safer materials arc developed, new methods offabricating them will permit them to be designed for a greater number of different purposes. What I have covered here is a bit ofhistory with the introduction ofonly a few current technologic developments. The knowledge of what is available must be coupled with refracting and prescribing skills that each of us needs to continue to hone. Only then can you prescribe properly and confidently - without making a spectacle of yourself! Acknowledgment 1 would

327

FUTURE

like to affirm my appreciation to the Foundation of the American Academy of Ophthalmology, which spon-

sors the AA0 Museum, and particularly Rosenthal, M.D., Walter H. Marshall, Cronenwett. for providing photographs, tive, and technical corrections for this

to thank J. William M.D., and Susan historical prrspecmanuscript.

References 2. Drew R: Pr&sional Ophthnlmrc IXrpe~~tn,y. (Ihiraso, Processional Press, 1970, pp 16S192 3. Hamhlin, D,J: What a spectacle! Eyeqlasscs and how the\ evolved. Smithsonian 13:10&l 10. Llarch. 1983 4. Holtmann HW: A history of spectacles, in Poulet M’ 1cd): .41/as on the Histot_v oJ~Spectac1e.r (translated by FC Blodi). Bonn, \?Vayenborgh, 1978, pp vii-xxi 5. Margulis I,: An optometric detective in search oI‘ antique evewear. ,I .4m Of&m .4.w1 ill: I357-1342. 197’1

‘l‘his paper was presented at the W.K. Kellogg Eye Crnter Dedication Symposium. University of Slirhiqan. Ann .\rhor. Slav 18. 1985. This report was supported in part by an unrcstrictcd drpartmrntal grant from Research to Prevent Bhndness, Inc. Reprint requests should be addressed to Llrlvin L. Robin. h1.D.. Universitv ofFlorida. College ofMedicine. Department ol’Ophthalmology, Gainesville, FL 32601,