The Hirschberg test is an objective means of determining the angle of strabismus by noting the distance the corneal reflex of a light source is from the center of the entrance pupil. A scale factor is used in converting the amount the reflex distance is in millimeters to prism diopters. Recent studies have demonstrated this factor to be 22 prism diopters for each millimeter. This study notes how axial length would effect this scale factor. Using ultrasound axial lengths of thirty eyes were measured and compared to the results of a Hirschberg simulation. A small effect results from this comparison. The mean values of scale factor determination noted twenty-three prism diopters per millimeter.
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