McClean Tonometer 1919
The McClean tonometer is a rare American hand-held contact tonometer first designed in 1919. It measures intraocular pressure — the critical diagnostic indicator for glaucoma. This example was manufactured by E.B. Meyrowitz, Surgical Instruments Co., 520 Fifth Avenue, New York, one of the leading American surgical instrument makers of the early 20th century. Read the history of tonometry at the College of Optometrists.
How the McClean Tonometer Works
The instrument features two small vertical handles. The clinician holds these between the fingers while lowering the instrument onto the patient’s cornea. A foot plate makes contact with the eye’s surface. The post then indents the cornea away from the foot plate. Depending on the firmness of the eyeball, the indicator needle deflects to a reading on the scale. That reading, expressed in millimeters of mercury pressure, indicates the intraocular pressure.
Comparison with the Schiotz Tonometer
The McClean tonometer operated on principles broadly similar to the better-known Schiotz tonometer, which also used indentation to measure eye pressure. However, the McClean design carried no weights. Its readings tended to run higher than other instruments of the period — up to 40 mmHg in some cases. The box instructions note that normal pressure falls between 22 and 40 mmHg, a range now understood to sit above modern clinical norms. This reflects the evolving science of glaucoma diagnosis in the early 20th century.
A Significant Moment in Glaucoma History
Glaucoma has challenged clinicians for centuries. Reliable pressure measurement proved essential to both diagnosis and treatment. The development of hand-held contact tonometers like the McClean design brought this diagnostic capability directly to the bedside and consulting room. The McClean tonometer represents an important chapter in that story — an American contribution to a field previously dominated by European instrument makers.
Maker and Provenance
E.B. Meyrowitz was a respected name in American ophthalmic and surgical instrumentation. The firm operated from Fifth Avenue in New York and supplied instruments to physicians and hospitals across the country. This complete example, with its original case and scale, provides exceptional documentary and display value.
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