. X-ray observations for foreign bodies and their localisation . Illustration 21. The geometrical construction on the lateral tracing foreign body in the posterior quarter. To ascertain if the movement of the foreign body corre-sponds to the rotation of the eye, a long ruler, fitted with amovable electric lamp, is placed at a known distance from thepatient and used to direct his gaze, and the displacementsabove and below the central or horizontal position are this information (using cm. to represent metres) the anglethe eve has turned through can be reconstructed on
. X-ray observations for foreign bodies and their localisation . Illustration 21. The geometrical construction on the lateral tracing foreign body in the posterior quarter. To ascertain if the movement of the foreign body corre-sponds to the rotation of the eye, a long ruler, fitted with amovable electric lamp, is placed at a known distance from thepatient and used to direct his gaze, and the displacementsabove and below the central or horizontal position are this information (using cm. to represent metres) the anglethe eve has turned through can be reconstructed on the lateral X-Ray Observations for Foreign Bodies 33 tracing, showing definitely whether the foreign body has turnedithrough the same angle. (Illustrations 15, 26-27-31.) In those tracings which show that the foreign body hassmoved, and yet the centre of the circle on which the shadows. Illustration body in the superior I. The elevation of the eyeproduced by the contraction of thesuperior rectus muscle causes theforeign body to be pulled nearer tothe fixed insertion of the muscle(Shadow I). When the eye is lowered the reversetakes place. The superior rectus islengthened, displacing the shadow ofthe foreign body to the oppositeside (shadow 2) of the zero position■(shadow 0) which is the shadowformed when the patient gazed tothe horizon. The Frontal Tracing. Fig. 2. The movement of adduction ^has hardly moved the foreign body; the two shadows overlie. Illustration Body in the I. In this case theloweringof the eye produced by the con-traction of the inferior rectusdraws the foreign body nearerto its fixed insertion (shadow 2),while the elevation of the eyeby the contraction of thesuperior rectus lengthens theinferior and again displaces theforeign body to the oppositeside (shadow I)
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