[The relation of the motion velocity of the real image to the velocity of illusory image in diplopia studied by the clock method].
From a perspective of 34 years' experience of using the clock method to examine ophthalmo-plegia, the author assesses the utility of this method and discusses the ensuing principles. He gives a thorough analysis of the principle which states that if the real image traverses a circular (or semi-circular) path then the apparent image moves in the same time along an elliptic (or semi-elliptic) path. According to his calculations the velocity of the apparent image is greater than the velocity of the real image and proportional to the magnitude of the disparation. The velocity of the apparent image is also important in the process referred to by earlier authors as "diplophobia". The present author gives his own simplified formula for the calculation of the circumference (or surface area) of the ellipse.