Since children’s eyes are highly adjustable and their own adjustments can cause errors of about 300 degrees or more, children and adolescents must have their pupils dilated before optometry and prescription lenses. The purpose of dilating the pupil is to relax the ciliary muscle in the eye and to relax the regulation. Only when the eye is relaxed can an accurate prescription be measured. In addition, dilated pupils can identify true and false myopia, the latter of which does not require prescription lenses. At the same time, dilated pupils can also play a role in preventing the development of myopia. There are two main types of eye dilators: 1) fast-acting eye dilators, mainly tropicamide eye drops; 2) strong, long-acting eye dilators, mainly 1% atropine eye ointment. The method of pupil dilatation depends on the individual circumstances of each child and is determined by the doctor.