Three-way mirroring is generally not harmful to the eyes. Three-sided mirror examination is generally a means of examination to check whether the optic nerve, retina and macular area have lesions. The inclination angles of the three mirrors are 75°, 67° and 59° respectively, and the reflections of the mirrors at different angles can be utilized to observe the changes of the anterior and posterior cornea and anterior and posterior capsule of the crystalline lens, to observe the corneal epithelium or endothelial edema, and to observe whether there is lesion in the periphery of the vitreous humor and the eye fundus. Three-sided mirror examination may cause eye discomfort, and some patients may experience slight interference and pain in the eyes, but they usually recover on their own the next day and do not go on their eyes. Moreover, the center concave lens of the three-sided mirror will not contact the cornea, and will not cause damage to the corneal epithelium or cross-bacterial infections, so there is generally no damage to the eyes. Patients who experience discomfort in their eyes after performing a three-sided mirror examination are advised to seek medical attention in a timely manner.