An apparatus for diagnosing and/or quantifying the degree of strabismus is disclosed. The apparatus includes a beam that supports at least two targets, a video camera, a light source for generating Purkinje reflexes, and a computer. The patient gazes at the targets while the video camera captures the patient's eyes. The frames of the video are then analyzed as described herein to determine the location of the pupil and the first Purkinje reflex. With this information, strabismus can be diagnosed, as well as the angle of deviation, which is useful for surgically correcting the strabismus. Methods of analyzing the frames are also discussed herein.