A welder wears protective eyewear to shield his eyes from the actinic rays produced by a welding arc. Intense bright light of this sort can be very damaging to the inner lining of the eye and may result in partial or permanent blindness. Although sunglasses with a light tint are sufficient for eye protection from the sun, a much deeper tint is required to protect the eyes during welding operations.
Glasses are worn to protect the eyes as well as to correct visual defects. The colored glasses, or sunglasses, worn to protect the eyes against the rays of the sun are a familiar example. To protect their eyes from the actinic rays of welding flames, workers wear glasses of a deeper tint. Machinists and other factory workers wear glasses or goggles of great strength to shield their eyes from flying particles of metal, and aviators and racing drivers wear goggles to shield their eyes from the wind. Watertight goggles permit divers to see under water.
In 1268 the English philosopher Roger Bacon recorded the earliest statement about the optical use of lenses. Possibly as early as the 10th century, however, the Chinese had made use of magnifying glasses placed in frames. Eyeglasses were first used in Europe in Italy, and some portraits dating from the Middle Ages depict 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 for Benjamin Franklin at his suggestion about 1760. In early times the only eyeglasses having spherical lenses were manufactured to correct nearsightedness and farsightedness. Not until the end of the 19th century did the cylindrical lens for the correction of astigmatism come into common use.
Optometrists, also called doctors of optometry, are specialists who examine the eye for defects and prescribe the use of corrective lenses. The actual lenses are then made by an optician.
Today, the doctor of optometry (O.D.), called an optometrist, examines the eyes for defects of vision and prescribes corrective eyeglasses or contact lenses. In Europe, this specialist is known as an optician or ophthalmic optician, but in the United States the optician is concerned with making lenses and spectacles. In contrast, the oculist, or ophthalmologist (M.D.), specializes in medical or surgical treatment of eye diseases or abnormalities of the eye.