A-scan ultrasound biometry is one of the numerous ophthalmologic diagnostic procedures. It is a type of ultrasound that uses sound waves to measure and produce detailed images of the eye. Specifically, the A-scan ultrasound takes measurement of the eye most useful in determining the correct lens implant for cataract surgery.

An A-scan ultrasound works by producing an image of structures in the interior of the eye. A numbing drop is placed in the eye to minimize sensations during the exam. The probe of the A scan touches the surface of the eye. To get the most accurate measurement possible, both eyes are usually measured and the lengths are compared.