What is the inspection method and clinical significance of three-sided mirror?

Three-sided mirror plays an important role in examining fundus with slit lamp, and it is simple to operate. With the help of three-sided mirror, it is easy to distinguish the difference between optic papilla, retina and choroid, which is of great help to distinguish cyst, hemangioma, retinal hole and choroid tumor, and to observe the relationship between retinal surface and posterior limiting membrane of vitreous body, the serosity of retina and choroid and the observation below retinal detachment.

Before the examination, the pupil should be fully dilated. First, a topical anesthetic is dripped, and methyl cellulose is dripped on the concave surface of the three-sided mirror that contacts the cornea, and then the concave surface is placed in the conjunctival sac to make it close to the cornea, and then the light is projected at a small angle (but not zero degree), and the fundus is observed with the three reflecting surfaces of the three-sided mirror respectively.

The inclination angles of the three mirrors are 75, 67 and 59 respectively. Mirror 1 can clearly see the central part of the fundus, mirror 2 can clearly see the part from the equator to the fundus 30, mirror 3 can clearly see the peripheral part, and mirror 4 can clearly see the angles of the vitreous body, the peripheral part of the fundus and the anterior chamber.

Before using the three-sided mirror, the pupil should be fully dilated. When the pupil is dilated above 8mm, the serrated edge and surrounding area are easy to observe.