This is a test to measure the shape and size of the eye. It is commonly used to calculate the power of intraocular lens (IOL) implants required for cataract and refractive surgery. Biometry can be performed using either optical coherence interferometry or ultrasound technology. This equipment is able to measure the length of the eyeball (axial length), curvature of the cornea (keratometry) to have the IOL lens powers for each individual eye.

Ultrasound biometry  is a non-invasive test performed by placing your chin on the instrument chin rest and focussing on a target light. It takes only a few minutes to perform. involves placing an ultrasound probe on the surface of the cornea to obtain measurements of axial length. A local anaesthetic eye drop is inserted into the eye before this test is performed. These can then be used along with keratometry measurements to calculate IOL lens powers.