This instrument is used for precise exophthalmos readings (e.g. exophthalmic goiter). The basis of the reading for exophthalmos determination using the Hertel version is the outer orbital rim (orbital wall) and the apex of the cornea. The integral refraction mirrors with millimeter scales for the left-hand and right-hand reading halves of the exophthalmometer are calibrated so that the zero mark on the scale will be located in the plane of the resting points of the supports. For exophthalmos readings, the supports are placed against the two temporal orbital walls so that the orbital rim contacts the deepest point of the supports.