An ultrasonic technique using microsurgical instruments that allows a cataract-affected lens to be liquefied and removed by suction using a very small incision near the edge of the cornea.

A foldable plastic lens is then inserted through the incision and unfolded.

A procedure in which the lens, clouded by a cataract, is broken up by ultrasound, irrigated, and suctioned out. Most cataract surgery today is performed using phacoemulsification.

Before the advent of this technique, people with cataracts could expect a ten-day hospital stay followed by a lengthy recovery. Today, it is an outpatient procedure.

Instead of making a large incision in the eye and removing the lens, the ophthalmologist can make a tiny one and then insert an ultrasonic tip which, vibrating thousands of times a second, breaks up the cataracts without damaging the surrounding tissue. The remains of the cataract are suctioned out.

The word phakos in Greek is a "lentil" (a lentil bean). The prefix phaco- therefore refers to the lens of the eye which is lentil-shaped.