Under normal circumstances, the refractive parameters of the eye are matched. Once this balance is broken, the refractive power of the eye is not coordinated with the axis length, and the parallel light is not accurately focused on the retina after refraction by the refractive system of the eye, it is called refractive error. When refractive error exists in the eye, the vision is blurred, if the ophthalmologist diagnoses refractive error, it should be optometry and glasses. Optometry is the process of using various ophthalmic instruments to examine the refractive state of a patient to determine the type of refractive error and the number of diopters that should be corrected, a process called optometry. Whether in the hospital or optician general optometry will use “automatic optometry (or computerized optometry)” for optometry. Some people will be based on the refraction (myopia, hyperopia or astigmatism) measured by the automatic optometrist, direct prescription lenses, which is not accurate enough. The standard method of optometry is in the automatic optometry measured the degree, but also should be applied to the manual optometry, the automatic optometry measured the refractive error to review, and then to match the glasses. If you are under 15 years old, you should use eye medication to dilate the pupil (after ciliary muscle paralysis) before optometry and glasses (children must be dilated after optometry). If you are 15 years old or older, you can usually get an eye exam without dilating your pupils. Because children and teenagers have strong ciliary muscle regulation, the results of optometry without dilated pupils (after ciliary muscle paralysis) are prone to errors. The purpose of dilating the pupil is to relax the ciliary muscle so that it is completely paralyzed, thus avoiding the effects of pseudomyopia and making the prescription accurate. After the pupil is dilated, the patient will experience temporary photophobia and blurred vision, which can recover on its own after a period of time, and even if the pupil is dilated several times, it will not bring harm to the eyes. It is best to have a corrected visual acuity of 1.0 when getting glasses. Some people who wear myopic lenses always want to have a corrected visual acuity of 1.5 or even higher, thinking that the higher the visual acuity, the better, but in fact this is often overcorrected, thus destroying the adjustment function of the eyes, causing visual fatigue and even deepening myopia. When wearing nearsighted glasses, the minimum myopia prescription that can reach 1.0 vision should be used to ensure that the eyes are clear and bright when looking at the distance, and not overly fatigued when looking at the near. Clear vision is not the only function of glasses, quality glasses should also make the eyes comfortable. If any of the following situations occur after wearing glasses, you should consider that the glasses are not suitable and may be overcorrected: easy to serially read at close range, reading time can not last, easy to swell the eyes and headache, look close and feel blurred when looking far away, dizzy when shopping at the mall, look close to the habit of taking off glasses, etc., such as timely detection as soon as possible to correct the damage caused by overcorrection is reversible. In order to avoid wearing overcorrected glasses, you should go to a hospital ophthalmology department for medical optometry.