A visual acuity device measures the visual acuity of a patient's eye by directing a pulsating beam of light on the eye and detecting the resulting reflection. A primary pattern having a pattern formed by transparent and non-transparent portions is positioned in the optical path of the pulsating beam...http://www.google.com/patents/US4257689?utm_source=gb-gplus-sharePatent US4257689 - Pulse pattern visual acuity device
