Automatic strabometry by Hough-transformation and covariance-filtering

In order to measure the angle of squint, the eyes of a patient are photographed using two CCD-cameras. Three hashes are activated at the moment of exposure. By measuring the positions of the reflexes in the digital image the squint angle can be determined. This paper presents a segmentation method for the automatic detection of the reflexes without the use of fixed threshold values. With an algorithm based on Hough-transformation the centre of the iris is localized. In the region of interest the reflex positions are located using cross-covariance-filtering. A classification and plausibility control follow to make sure there are no faulty measurements. With 191 clinical images arbitrarily chosen the algorithm was tested showing perfect results. It is already used in clinical practice