The A-Scan is a type of ultrasound, radar-like device that emits very high-frequency waves that are reflected by the ocular structures and converted into electrical impulses. It is used for differentiating normal and abnormal eye tissue or for measuring the length of the eyeball. It also helps in determining the refractive power of the intraocular lens implant that is used to replace your eye’s own cloudy lens in cataract surgery.