An autorefractor is a machine used to measure a person's refractive error and prescription for eyeglasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye. The automated refraction technique is quick, simple and painless. The patient takes a seat and places their chin on a rest. One eye at a time, they look into the machine at a picture inside. The picture moves in and out of focus as the machine takes readings to determine when the image is on the retina. Several readings are taken which the machine averages to form a prescription. No feedback is required from the patient during this process.