M-Mode, or time-motion display, allows a single beam to emit from the ultrasound transducer along a defined track in conjunction with a recorder that captures all motions that occur along the path. This mode allows high temporal resolution, thus affording the examiner an excellent view of subtle motions. Clinically, this mode is ideal for capturing vessel diameter changes, movement of cardiac valves, and detecting fetal heartbeats. The use of the M-mode or time-dependent intensity-modulated ultrasound technique for ophthalmologic investigations is described here. This technique provides the investigator with a means for monitoring structural changes in the eye during physiologic or pharmacologic experimental conditions, or a combination of both, and is particularly useful in studying optically inaccessible structures. The technique has been used to study accommodation changes in axial length and lens thickness as well as the rate of such changes and to study vascular pulsations and choroidal thickness changes at the rear wall of the eye.