In this test, the eye is examined by ultrasound . The ultrasound uses high frequency sound waves that are emitted and received by a transducer (a hand-held instrument), and the sound waves penetrate the body. Based on the waves recorded, it is possible to determine if the structures being examined are functioning properly. An echoencephalogram can also be used to examine the cerebral structures (for example, in checking for hydrocephalus ), although it is more commonly used for eye disorders.