A scan ultrasound biometry, commonly referred to as an A scan (short for Amplitude scan), is most commonly used for measurement of axial length (AL), which is critical for intraocular lens (IOL) calculations prior to cataract surgery.

B scan ultrasound refers to a two dimensional, cross section brightness scan. It is typically used to evaluate posterior segment and orbital pathology. Ultrasonic pachymetry is a common and quick method of obtaining the corneal thickness on a single point on the cornea