A fine and fully functional antique Hertel mirror exophthalmometer dating from the mid-1950s to mid-1960s, made by Handaya Co. of Japan and imported by the now-defunct company Optical Imports Co. of Bellingham, WA. Presented in its original fitted green case, this is a well-preserved example of a mid-century clinical instrument whose fundamental design has remained essentially unchanged since it was first commissioned by Hertel and made by Zeiss in 1905.
The Hertel mirror exophthalmometer was designed to measure the position of the eye in a forward and backward direction relative to the outer part of the eye socket — a measurement critical in the diagnosis and monitoring of proptosis (exophthalmos), most commonly associated with thyroid eye disease. The instrument consists of two identical frames that move along a connecting bar, with side rests that are placed on the outer rim of each eye socket. Each frame carries a long narrow mirror tilted at 45 degrees, allowing the clinician to see the image of the apex of the cornea reflected in the mirror. A millimeter scale on the outer side of each frame is then reflected by a second narrow mirror, and the scale’s image is superimposed on the image of the corneal apex to give a direct measurement. When the instrument was originally designed in 1905, 20mm was considered the average value for the corneal apex protrusion relative to the lateral orbital rim.
This example is unchanged in design from the original model made for Hertel by Zeiss over 120 years ago — and it still works just fine today.
