The difference between dilated optometry and non-dilated optometry lies mainly in whether the local ciliary muscle of the eye is in a state of paralysis and relaxation, which can directly affect the refractive error. Dilated optometry, the ciliary muscle is in a state of paralysis and relaxation, due to eye fatigue, tension and other reasons for visual acuity deviation, will be reduced accordingly, or even disappear, at this time the results of the optometry is relatively accurate. In the case of non-dilated optometry, the ciliary muscle may be in a state of tension, and the spasm of the ciliary muscle may result in a false reading, thus affecting the results of the optometry and causing errors. Therefore, it is recommended that first-time eyeglass wearers, especially children, consider a partial dilation of the eyes before performing an optometric examination.