Laura Buckman, age 14, of Laconia, N.H., for her question:
WHEN WERE EYEGLASSES FIRST USED?
Eyeglasses are lenses or prisms worn in front of the eyes to compensate for various defects of vision. In 1268, English philosopher Roger Bacon recorded the earliest statement about optical use of lenses.
Possibly as early as the 10th Century, however, the Chinese made use of magnifying glasses placed in frames.
Eyeglasses were first used in Europe in Italy. Some portraits dating from the Middle Ages depicted persons wearing eyeglasses.
With the invention of the printing press in the 15th Century, the demand for eyeglasses increased and by 1629 was large enough for a charter to be granted to a guild of spectacle makers in England.
The first bifocal glasses were made in the United States about 1760 at the suggestion of Benjamin Franklin.
In early times the only eyeglasses having spherical lenses were manufactured to correct nearsightedness and farsightedness. Not until the end of the 19th Century, however, did the cylindrical lens for the correction of astigmatism come into common use.
Today the doctor of optometry, called an "optometrist," examines the eyes for defects of vision and prescribes corrective glasses or contact lenses. In Europe, this specialist is known as an "optician" or "ophthalmic optician," but in the U.S. the optician is concerned with making lenses and eyeglasses.
In contrast, the "ophthalmologist" specializes in medical or surgical treatment of eye diseases or abnormalities of the eye. This doctor has an M. D. degree.
The lenses of eyeglasses are ground in the form of concave spherical lenses for nearsightedness (myopia), convex spherical lenses for farsightedness (hyperopia), cylindrical lenses for astigmatism and prisms for defects of convergence.
Often it is necessary to grind lenses in a combination of forms to correct several anomalies at once.
Bifocal lenses are used to give a different amount of correction for vision at a distance and for close work. The upper part of such lenses is ground for distant vision and the lower part for close vision, so that the user has merely to lower the eyes to read and raise them to look at objects that are some distance away.
Trifocal glasses are bifocals that are ground with a center lens for intermediate distance.
The inconvenience of conventional eyeglasses led to the development of plastic corrective lenses that can be worn under the eyelids, directly over the eyeball. Such contact lenses minimize the danger of breakage that is always present with ordinary glasses, because, like the eye, contact lenses are protected from injury by the shape of the skull.
Present day contact lenses cover only the cornea of the eye.