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March 1959

Tonometry—Effect of Tonometer Footplate Hole on Scale Reading: Further Studies

Author Affiliations

St. Louis
From the Department of Ophthalmology and the Oscar Johnson Institute, Washington University School of Medicine.

AMA Arch Ophthalmol. 1959;61(3):373-375. doi:10.1001/archopht.1959.00940090375006

In 1958 Moses and Hahn1 investigated the inconsistency of the low scale readings of the Schiotz tonometer noted in the report of Kronfeld2 and found to cause unintelligible results in tonography.3 We found that at low scale readings (high pressures) the cornea bulges into the hole of the tonometer footplate, unduly elevating the plunger and exaggerating the estimate of intraocular pressure.

At the request of the Committee for Standardization of Tonometers, attempts have been made to quantitate this effect further.

Method  A tonometer with four interchangeable footplates was secured, the hole diameters being 3.3, 3.7, 4.0, and 4.5 mm., respectively.* All measurements were made on patients by me, with use of the technique previously described of obtaining a scale reading first with the footplate with the

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