Glasses inconvenience brought to CONTACT LENSES correction development, and not only from plastic which can be worn under the eyelid, directly on the ocular eye. These CONTACT LENSES minimize radically the breaking risk, which is always present at normal glasses, because the contact lens is being protected by its shape, as the eye by skull shape. Nowadays lenses cover only the eyes cornea. So called soft CONTACT LENSES are used frequently and they are formed from a soft plastic, which casts on the eye.
Glasses
Lenses or prisms wear in front of the eyes for compensate different sight problems. The most usual shape of glasses is: a pair of glass lenses, in a metal or plastic frame and with the prop for nose. The frame is being hold by screws or arms, which catch the head or the hook behind the years.
There are also used: – protection glasses, also called sun glasses;
* glasses for swimming;
* glasses for protection in buildings.
contact lens History
The first lenses are from the time of Greeks and Romans, where glass spheres were filled with water. Those lenses filled with water were used as glasses with fire. The real glasses didn’t appeared in classic times; they were manufactured for the first time at the end of the 13th century, in Europe. The process of lenses fabrication didn’t changed too much since the Middle Ages, beside the utilization of grinding degree, introduced by Isaac Newton.
The recent developments of plastic and special processes for modulate them, brought to the increase of lenses production. Plastic lenses are easier, cheaper and less fragile then the ones from glass.
In 1286, the Englishman Roger Bacon registered a declaration about optic lenses utilization. Glasses were first used in Italy, Europe. Starting with the 15th century, the request for glasses increased so that in 1629 had become a real business.
The first pair of bifocal glasses was made by Benjamin Franklin in 1760.
Lenses are used in optical systems from glass or any other transparent substance, with a form that allows refracting the light of any object of real or virtual shape. CONTACT LENSES and lenses from glasses are used in medical purposes.
Lenses are also used at microscopes, telescopes and other optical tools.
Lenses producing
In most cases, lenses are formed from a kind of superior quality glass. This is called also optical glass, which has no internal defects, air bubbles or other flaws. The process of making a lens from a glass block implies a few operations. The first step is tracing a shape of lens on the glass block. After its cut, it’s pressed with a piece of thin metal, whose edges are strewed with diamante powder.
The piece of glass it’s brought to its shape by cutting it with an iron plate covered with a mixture of water and adhesives.
For obtaining the lens surface are used concaves or convexes tools, loaded with abrasives.
The finishing process of the lens is the grinding, and after that, the last thing is to cut from the edges, so that they will be equal