Automatic measurement of the angle of squint by Hough-transformation and covariance-filtering

Describes the image processing method for the automatisation of the measurement of squint using the first and fourth Purkinje reflex. This method is already in use in clinical practice in comparison to the standard method of the cover test. The new method, based on image processing, allows the exact and objective determination of the angle of squint. Children from the age of six months as well as adults can be examined. The automatisation of the previously interactive method is a prerequisite for the screening of large collectives of children for microstrabism. The method uses a two-stage abstraction to identify six reflexes in the iris of each eye. The method based on the Hough-transform and covariance-filtering is robust against image distortions and additional reflexes, as produced by wearing glasses. The reliability of the method has been proven in 191 cases and is tested in routine use now