Ultrasonography uses ultrasound to image tissues within the body. A-scan ultrasonography provides a one-dimensional view of the eye by measuring the echoes of ultrasound waves. It can be used to detect and measure tumors, assess eye structures for IOL calculation, and interpret pathology. The ultrasound is reflected at interfaces between tissues, appearing as spikes on the display. Immersion techniques provide more accurate measurements than contact techniques by avoiding compression artifacts. Limitations include artifacts, small lesions, missed foreign bodies, and misalignment issues.