Antiquity
No one knows when the earliest vision aids were used. There are no written recordings from early times. No paintings or sculptures showing optical devices or specimens from these times are available; the earliest known representation is in a church mural from the year 1270.
The ancients were surely aware of the optical effects of water or glass, for example, the magnifying effect of a drop of water, the enlarged view of a leaf vein seen through a dewdrop, or the visual effect through a spherical transparent jewel of the underlying surface.
Recent findings have shown that the Egyptians and Babylonians knew and used rules of optics. An optically useful lens with a refractive power of approximately +9.00 diopters was unearthed in Nimrod. Two optically polished spheres were found in the tomb of Tutankhamen, currently stored in the National Museum in Cairo.
Several optically excellent quartz spheres representing the eyes of a pharaoh were found among burial gifts. They still can be used as magnifying glasses for reading. Eyes in the statue of the god Horus in the British Museum in London show aspheric corneal surfaces, similar to the corneal curvature of a human eye. Collections of lenses in the museums of Cairo and of Athens indicate that the production of visual aids seems to have developed in parallel with the invention of writing. The rarity of the devices and reports perhaps reflects the limited population requiring such devices (i.e., priests and high public officials).
Earlier writings do not contain references to visual aids. The earliest description of sunglasses was made by Pliny (23–79 bc ). He wrote that the Roman emperor Nero used a polished emerald to view the gladiators. He does not mention if the optical surface was spherical, but it is apparent that the light-absorbing nature of the gem made viewing in bright sunlight more pleasant. From the same era, one can read complaints by older Roman statesmen that the condition of their eyes made reading of legal texts difficult. It is likely that presbyopia was considered a disease in ancient Rome, but no one documented any treatment with visual aids.
The beginning
The earliest mention of a visual aid was the reading stone ( Fig. 46.1 ). It was described by the German poet Albrecht in 1270 as a magnifying glass. In the same year, Konrad of Wuerzburg wrote about a crystal that enlarged printed letters. The shape and the polished surface reminded him of a large drop of water that when laid on a printed page greatly increased the size of the text. The stone was a polished hemisphere of the semiprecious gemstone beryl, which when laid on a page enlarged the text in all directions. The refractive power was +15.00 to +30.00 diopters, a power too great to correct presbyopia by wearing close to the eye.
Early eyeglasses
The inventor of spectacles, meaning glasses worn directly on the eyes, is unknown. Ptolemy wrote in about 125 bc concerning the enlarging ability of a spherical glass lens; the Saracen mathematician and astronomer Alhazen published the laws of refraction in 1028. The Oxford Franciscan monk Roger Bacon noted in 1267 that a presbyope could read the smallest printed letters with the aid of appro-priately polished lenses.
Classic spectacles that are worn directly over the eyes appeared in more recent times when clear, transparent glass became available at a reasonable price. This first occurred on Murano, a small island near Venice still famous for the production of glass. There was mention of such eyeglasses in the official state documents around 1300. Developments from spectacle manufacturers no longer required that the lens be placed on the text to read; it could now be held in front of the eye. The earliest sample of such a spectacle is a single lens in the Church of Konstanz dating from 1270. The first colored painting showing this type of reading glass, constructed like a magnifier ( Fig. 46.2 ), dates from 1352 and is in the church of San Nicolo in Treviso, a small city near Venice. In this church, one can also view the first representation of two lenses bound together, called rivet spectacles .
Rivet spectacles
The early example in Fig. 46.3 shows reading aids as a single lens or a pair of lenses called a lorgnon , which developed into modern spectacles. Two such lenses fixed together were designed to be held in front of the eyes to enable binocular reading. The two lenses were attached by a strap riveted to the frame of each lens, which enabled a variable interpupillary distance. This method of fabrication resulted in the name rivet spectacles.
Representations of this type of spectacle are frequently found in 15th- and 16th-century paintings; they enabled the clergy to read from scripture as is represented in the altar paintings shown in Figs. 46.4 and 46.5 . The cathedral in Ulm has a stained-glass window dated 1438 showing Peter with a pair of rivet spectacles. The earliest printed representation of a rivet spectacle is in the World Chronicle of H. Schedel printed in Nuremberg in 1498. In this illustration, noted physicians, researchers, and scientists of that period wore rivet spectacles as signs of their educated background ( Fig. 46.6 ).
Samples of rivet spectacles are rare; the oldest were found in the cloister at Wienhausen in Germany. These visual aids had been hidden during a war and forgotten for many centuries. The frames were made of beechwood fixed together with copper rivets. By this simple technique, the lenses could be made to fit any interpupillary distance and be centered over each eye.
Manufacture
The increased market resulted in the production of glass reading glasses in Murano either by grinding and polishing or by casting in metal forms. The resultant high cost limited them to those who could afford them. The strength ranged from +2.00 to +3.00 diopters based on the requirements of the reader. This age group was 40 years or older, an age not attained by many in this time.
Glass lens manufacturing did not remain a Venetian monopoly for long. Efforts at duplication and improvements were made in many other countries, but initially Italy remained the only source of the glass. Numerous cities, for example, the free cities of Nuremberg and Augsburg, established firms solely for producing and selling reading lenses ( Fig. 46.7 ). These organizations soon established rules and regulations to guarantee quality control and thereby improve the marketability of their products. Competition of cheaper products was a factor; an early conference was held in Nuremberg to codify lens production and define the profession of spectacle manufacturers. To ensure quality control a guild was founded, and in Paris and London the regulations for teaching and awarding of Masters’ documents were codified.
Minor improvements were made during the first century of spectacle making: better lens polishing, new methods of stabilizing the positioning of spectacles for reading, and some improvements in lens casting. The 16th and 17th centuries saw the appearance of less expensive spectacles, usually + 3.00 diopters intended for presbyopes, framed in leather or iron. Products with horn, copper, or brass frames were made for the clergy or public officials, whereas those framed in gold, silver, or ivory were rarities reserved for the very wealthy.
We know more about the price of spectacles during this era than production details. Although cheap imports from Italy were available, none were reportedly sold through peddlers. Quality spectacles were available only from approved spectacle makers. Lenses framed in horn or leather ( Fig. 46.8 ) cost, on the basis of current value and quality, about 5 US dollars. This reflected the cost of currently available cheap glasses produced by mass production techniques.
