This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables.
To the Editor:
—The article Fast Acting Applanation Tonometers by Schulz, Hilton, and McEwen (Arch Ophthal 69:717-721, 1963) was quite instructive, but perhaps from experience with the Mackay-Marg tonometer, there are a few useful details that might be added.The theory of these instruments demands that some sort of transducer be surrounded by a coplanar insensitive annulus, and the condition of coplanarity should be well satisfied. Thus, our experiments employed a stiff support and an extremely sensitive transducer. We felt in our original article, that the ionization converter circuit was not sensitive enough (if used in a rugged configuration). The device they describe shows a change of plunger position of 6μ when tilted from upward to downward. As can be seen from one of our later papers (Mackay; Marg; and Oechsli: Nature 194:687-688 [May 19] 1962), this means that there will only be one orientation of this probe for which
Mackay RS. FAST ACTING APPLANATION TONOMETERS. Arch Ophthalmol. 1963;70(5):733-734. doi:10.1001/archopht.1963.00960050735025