When you want to change your glasses, if you need the prescription of your previous eye, you need to have it re-measured. At present, there is an instrument in the optical store, called top focal length meter, top focal length meter as long as the lens is placed under the mirror of the focal length mirror, through the adjustment of the instrument, automatically will measure the degree of this glasses and the axis of astigmatism to astigmatism, these will be accurately measured. An accurate pair of glasses: 1, the lens prescription should be accurate; 2, the pupil distance measurement should be accurate; 3, need to try on. The result of trial wear is to see things clearly and without discomfort, which is the requirement of a better pair of glasses. If there is halos or discomfort in looking at things, then the glasses should be readjusted.