Eccentric fixation may be measured in prism diopters in amblyopic eyes by means of a simple device. A pinhole slightly eccentric to the geometric center of a circular disc is used: as the disc rotates the observer observes entoptically a filmy pattern of his retinal vasculature. The method has been tested on 240 eyes and a high degree of correlation was found between the amount of eccentric fixation and the decrement in acuity.