By definition, ultrasound has frequencies above 20 kHz, above the human audible limit. Ocular ultrasound uses waves with frequencies of about 10 MHz produced by a small probe that is placed on the closed or open eye, as appropriate. With topical anaesthesia in the case of the open eye, or without anaesthesia with the eye closed, a gel is applied between the probe and the eye to remove air bubbles. This probe collects the echoes ("echo") of tissues that it translates into a two-dimensional image of the eyeball.

The denser the tissue, the brighter it will appear (hyperechogenic) and conversely, the more aerated, the less bright (hypoechoic). If the tissue is dense enough, it will also have a cone of shadow behind it, which is common in some tumours or intraocular foreign bodies. This non-invasive and painless technique can easily be performed in the office, during consultation, at the patient's bedside or in the operating room. Moreover, ultrasound can be easily performed on children without sedation.