The UBM is an instrument used to examine the atrial angle, most commonly for traumatic changes, and is necessary to visualize the structure of the atrial angle more clearly than an atrial angle lens, especially in cases of ciliary detachment. UBM is an ultrasound test that requires a little bit of epi-anesthetic and a probe that touches the surface of the cornea to measure the position of the atrial angle, which is a kind of ultrasound test.