Refractive errors (myopia, hyperopia, astigmatism) can affect life and learning, and need to be corrected early, no matter what kind of correction method is chosen, such as wearing ordinary frame glasses, corneal contact lenses (contact lenses) or even eye surgery, it is necessary to correct optometry as a prerequisite. There are two major types of optometry, one is obviously optometry, also called subjective optometry, is based on the patient’s self-conscious vision after wearing glasses to determine the refractive power. The characteristics of the method is relatively simple, does not need to dilate the pupil, fast, then you can know the results. At present, most opticians use this method, or combined with computerized optometry. The other type is objective optometry, which often requires dilating the pupil before optometry to eliminate the adjustment of the eye, which is especially helpful for children under 14 years old and improves the accuracy of optometry. However, its method is more complex and requires an examination by a highly trained professional or ophthalmologist. Glaucoma patients should not have dilated pupils, and people over 40 years of age generally do not have dilated pupils. After the dilated eye exam, further adjustments must be made in conjunction with a trial lens to determine the final refractive error.