Ophthalmic ultrasonography: A-scans

Ophthalmic ultrasound measures and visualizes the posterior pole; an A-scan produces a one dimensional display and the B-scan is two dimensional. A-scan measurements are indicated prior to cataract surgery because of their accuracy and repeatability. It measures the length of the eye along the visual axis from the cornea to the retina. B-scans are performed as a check for the A-scan or for extremely long or short eyes.