Today's eye glasses are most often made of plastic, The exact science of how eye glasses are made involves a very precise, very detailed system of events. After a patient's eyes are tested to determine whether or not eye glasses are needed, if it is determined that eye glasses will be prescribed, a technician then has the task of figuring out the patient's necessary prescription strength. A special computer is used in determining this and it prints the exact specifications for how to manufacture the prescribed lens for the patient's eye glasses. The physical creation of the prescribed eye glasses then involves the technician comparing a pair of plastic blanks until an appropriate one is found for the patient's prescription. The remaining prescription strength needed is then ground into the blanks at the back of the lens.Next is the blocking process, which is when the optical center of the eye glasses is located. More grinding sets the necessary degrees or curves that are needed to achieve the optical strength that the eye glasses need. The lens is then shaped or beveled, and polished to perfection.While different types of plastics are used in making glasses, a very lightweight polycarbonate known as "Featherweight" is the most durable, the most popular, and the most expensive. Also, if a patient prefers tinted eye glasses, the lenses are specially treated before being finally inserted into whichever frames the patient has selected.Because of advances in technology and the materials used, today's eye glasses are much more durable than in years past, and many people even regard them as fashion accessories.