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spectacles

spectacles Many claims have been made with regard to where spectacles originated. Both China and India have their advocates, but the best evidence is that they reached these countries from Europe via circuitous routes. The Romans considered myopia (‘short-sightedness’) a permanent defect that reduced the market value of a slave. However, ageing patrician Romans appreciated that the only way to counteract presbyopia (the refractive error of ageing) was to be read aloud to by a younger slave. Pliny wrote of Nero viewing gladiatorial events zmaragdo, that is, through beryl, one of a family of transparent green precious stones of which emerald is another. Nicolaus Cusanus first wrote of using concave lenses for myopia in his book De Beryllo in 1441. The word beryl has lived on as beryllia (Venice) and as Brille (German), meaning ‘spectacles’ — a word which itself comes from perspectare (Latin), ‘to look all about’.

A glass bowl full of water had been used as a magnifier and burning glass in antiquity. Roger Bacon (thirteenth century) wrote of looking through the ‘lesser segment of a sphere, with the convex side towards the eye’ to make letters and minute objects appear larger. Even today a simple magnifying lens — the monocle — is occasionally used as a temporary aid to reading, hand-held or kept in place over the eye by contraction of the orbicularis muscle that encircles it.

It was in Venice, the centre of glass making, that the first pair of spectacles appeared, around 1280. Two convex lenses mounted in a frame were used for presbyopia. Brother Giordano da Rivolto of Pisa, in a sermon in 1305, said, ‘It is not yet twenty years that the art of making glasses was invented; this enables good sight and is one of the best as well as the most useful of arts that the world possesses.’ Contrast this with the comments of Mr Cross, Vicar of Chew Magna in Somersetshire, who declared: ‘The newly invented optick glasses are immoral, since they pervert the natural sight and make things appear in an unnatural and a false light.’

The spectacles worn by Hugues de St Cher may be the first ever painted and are to be seen in the fresco by Tomaso da Modena in the Dominican chapter house of San Nicolo, Treviso, Italy, dated 1352. The earliest myopic glasses were painted by Jan van Eyck in the early fourteenth century. The Medici family provide a pedigree of myopia but Pope Leo X is the only member known to have used glasses. Raphael's painting of 1518 shows Pope Leo X holding his concave lens.

Reading corrections

The strength of reading glasses was originally based on the patient's age. For a man of 30–40 years lenses of 2 degrees were used, for 70–80 years, lenses of 4 degrees. Even as late as the second half of the nineteenth century, glasses were provided by itinerant pedlars. It is remarkable that in our present scientific age, when the appropriate corrective lenses can be prescribed on the basis of precise measurement of refractive errors, some people still choose their own reading glasses at the chemist's shop. Astigmatic correction was not generally available until late in the nineteenth century, despite Airy's cylindrical correcting lens (1827) and Donders' comprehensive book on refraction (1864). Benjamin Franklin devised bifocal lenses, originally for himself, around 1775, by cutting each lens horizontally from his distance and reading glasses, and then binding half from the distance pair with half from the reading pair into the same frame, with the stronger lens lower, i.e. in the reading position. Hawkins introduced trifocal lenses in 1826. Successful multifocal lenses, which have smoothly increasing power over the lower half of the lens, with no visible segment line, were brought in during the 1960s. Unfortunately, these lenses are such a compromise in optical terms, and the field of clear vision in the reading area is so small that, for even the short lines of print when it is in double columns, the reader is obliged to turn his head slightly to follow along each line. Multifocal lenses have their best chance of acceptance if introduced when presbyopia first appears as then the necessary increases in strength with age are more readily tolerated.

Optical defects

Spectacle lenses have inherent optical defects, such as chromatic and spherical aberration, some of which are correctable. It was early apparent that a fixed lens in front of a mobile eye could only be optimally focused in the straight ahead position. Side vision is distorted and oblique rays of light passing through a spherical lens produce astigmatism. Instead of having a spherical front surface with a flat (plano) back, a lens with a more strongly convex front surface and less convex back was devised. Similar double curvatures were used for concave lenses, and even more complicated corrections for astigmatism.

Special lenses

Originally made of glass, with the dangers of breakage and eye injury, most spectacle lenses are now made of plastic — they have to be by law if they are for children or for adults with dangerous occupations. Lenses can be specially formulated to protect against radiation — principally ultraviolet light, but also against infra-red light. Photochromic lenses, which darken in sunlight and become lighter in the shade, now change colour at acceptable speed for most purposes. Another way of reducing glare is by ‘Polaroid’ lenses, which cut out much of the reflected light that has been partially polarized by reflection from water or from glass surfaces. Reflecting glasses, with an extremely thin metallic layer to reject harmful rays, render the wearer's eyes totally invisible behind the silver surface in a most disconcerting manner.

The author currently wears spectacles made of plastic, photochromic lenses with multifocal capabilities in a ‘rimless’ frame to be as light in weight as possible. But the definitive, all-purpose lens has yet to be devised. The huge choice of frames, of colours, and of lenses allows spectacles to make a fashion statement even if their physiological necessity is questionable. Finally, very dark or reflecting glasses may be used not only for purposes of anonymity but as a shield for an inadequate personality.

Peter Fells

Bibliography

Sorsby, A. (1948). A short history of ophthalmology, (2nd edn). Staples Press Ltd., London.


See also contact lenses; eyes; refractive errors.

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spectacles

spec·ta·cles / ˈspektəkəlz/ • pl. n. another term for glasses.

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