This instrument is used for precise exophthalmos measurements (e.g. exophthalmic goiter). The basis of the measurement 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 measuring 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 exophthalmus measurements the supports are placed against the two temporal orbital walls so that the orbital rim contacts the deepest point of the supports.