Alternative method of intraocular foreign-body localization.

Abstract

Anteroposterior (AP) and lateral films are obtained simultaneously, and superimposed on them is the shadow of a pair of cross wires representing the center of the pupil in the AP projection and the front surface of the cornea in the lateral projection. This is achieved by the use of a frame on which are mounted three sighting devices. Each sight is like a simple gunsight with two sets of cross hairs 80 mm apart; one of the cross hairs is radiolucent, and the other is radiopaque so as to be superimposed on the x-ray film. Two of the sights are mounted horizontally and are coaxial. These are the sights used for lateral projections; one is used for right eye localization and the other when left eye localization is required. These sights are positioned by adjusters in vertical and horizontal directions. The third sight is mounted vertically for the AP projection and can be adjusted laterally over a range covering both eyes. The center axis of this sight intersects the center axis of the lateral sights and moves with them if they are adjusted in a horizontal direction (inferior-superior movement with respect to the patient). In use, the patient is supine, the head is positioned on a thin foam pad between the lateral sights, and the neck is extended so that the outer canthus-external auditory canal baseline is 25#{176} to the perpendicular. The head is immobilized by means of a restraining band, and the sights are adjusted over the center of the pupil in the AP projection and to the front surface of the cornea in the lateral. The x-ray tubes are then positioned with the central ray in the axes of the sighting devices. The AP film is placed in a tunnel beneath the patient’s head, and the lateral film positioned next to the head on the contralateral side from the eye being examined (fig. 1). Simultaneous biplane exposures are taken, if possible with the patient’s eyes open and looking at the light beam collimator of the overhead tube. A focus-film distance of 1 200 mm is used for both projections to provide a standard magnification factor of 1 .2:1 (fig. 2). When necessary, plotting of the foreign body on an eye localization chart is achieved by taking direct measurements of the foreign body from the reference point (the pupil and front surface of the cornea) and transposing these measurements onto the chart after making appropriate allowance for magnification.