The so-called optometry is through the subjective or other sensory examination of the eye accurate refractive error, as the basis for the prescription of glasses. There are two methods of optometry: one is apparent optometry (also known as subjective optometry), optometry without dilating the pupil, but according to the patient’s self-perception of vision to determine the number of refractive error, the general opticians mostly use this method, its characteristics are relatively simple, fast, can be carried out in large numbers. This method is suitable for people over 40 years old, but for children under 12 years old, farsightedness, astigmatism, pseudomyopia, etc. are prone to errors. Therefore, a second method of optometry should be used, namely dilated pupil examination optometry (also called tachistoscopy). The following are the advantages of astigmatism: 1, pseudomyopia caused by regulatory spasms, once the pupil is dilated, the regulation disappears, and pseudomyopia is restored; so the pupil becomes a good method of treatment; 2, the regulation of the adolescent eye is very strong, if not dilated, there is a considerable difference in the degree of optometric error; 3, eyes with astigmatism, after the pupil is dilated, the degree of optometry and the position of the astigmatic axis can be checked more accurately; 4, the hyperopic eye is very strong adjustment, must be dilated optometry. Because the results of dilated optometry are objective, patients with amblyopia and low intelligence can be accurately checked for their prescriptions. Many patients do not understand what is going on with dilated pupils, so they are concerned about dilated pupils, fearing that they will damage their eyes and affect their vision. This idea is not based on science. The pupil is dilated by using drugs that act on the nerve that governs the pupillary sphincter and the large muscle, causing the pupil to dilate, and when the time for the drug to act has passed, the pupil will naturally return to its original state, causing no damage to vision. We usually use the following pupil-dilating drugs: 1, tropicamide, the action time is about five hours; also known as rapid pupil dilatation. 2. Atropine, which has a duration of action of about two weeks. The specific type of dilating medication to be used and the method of use should be done under the guidance of a doctor. When the pupil is restored to its original state after the dilated eye examination, a trial lens should be inserted once more to determine the final prescription to be used for finalizing the prescription lens.