Light beams of predetermined different wavelengths are projected into an eye fundus and light scattered therefrom is detected to distinguish blood vessels from surrounding tissue in the eye fundus. The method and apparatus of the invention makes full use of differences in light absorbing/reflecting characteristics...http://www.google.ca/patents/US5141303?utm_source=gb-gplus-sharePatent US5141303 - Method and apparatus for discriminating eye fundus blood vessels
