Glasses are reading or seeing lenses mounted on suitable frames with stems worn over the nose in front of the eyes, the stems are placed over the ears so that they do not fall off. They are worn for eye protection as well as for correction of vision.
Glasses were invented around the 11th and 12th centuries. Chinese imported the technology of glasses from the Middle East in the 11th century. Though there is no clear evidence about the inventor of glasses, one of the potential inventors is Salvino D’Armate of Italy and he is said to have invented glasses in 1284. Another person credited with the re-invention of glasses is a Dominican Friar, Fra Alessandro da Spina of Pisa. He is believed to have learnt how to make glasses after seeing them being made by the original unknown inventor. Early eyeglasses did not have stems. They were just balanced on the nose until 17th century.
Safety glasses are used for protecting the eyes from external objects like flying particles in areas of work, sparks from grinding during fabrication, and from intense heat and light during gas and arc welding in work shops. Sun Glasses are specially made glasses that protect eyes from ultra violet rays and radiation. Plastic lenses have become very popular due to their low weight, low dispersion, high scratch resistance, low transparency to infrared radiation and ultraviolet rays.
