A dilator is a medication that paralyzes the ciliary muscle and is a completely reversible phenomenon. When the effects of the medication are removed, the ciliary muscle returns to its undilated state and usually causes no harm to the eye. Pupil dilators are commonly used in ophthalmology and are commonly used to treat certain eye diseases and to perform funduscopic examinations. The purpose of dilating the pupil is to open the pupil wide for various examinations, to be able to see the structures of the fundus more clearly, or in the treatment of iridocyclitis, to promote the reduction of inflammation and relieve painful symptoms, and also to avoid pupillary adhesions. For the majority of patients, dilated pupils are safe. However, there are a few special people who have experienced side effects after having dilated pupils. Therefore, pupils should only be dilated under medical supervision after an initial examination of the eye structure. Dilated pupils include fast and slow dilatation, and recovery time varies between the two methods, but most can be fully recovered. In conclusion, dilated pupils are the main method of routine treatment for certain diseases and routine eye examinations, and safe dilatation under the guidance of a doctor will not harm the eyes.