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I read with interest the article by Kniestedt et al¹ in the September 2004 issue of the ARCHIVES. I would like to point out that a statement they made in the "Comment" section is inaccurate, although it does not significantly affect their conclusions. However, it does represent a misconception about applanation tonometry that appears occasionally in peer-reviewed articles as well as in ophthalmology textbooks.

Kniestedt and colleagues state that "Goldmann and Schmidt . . . set the applanation diameter at 3.06 mm so that the effect of corneal elasticity in an ‘average’ cornea would offset the effect of the capillary attraction of tears."¹ In fact, this precise diameter was chosen simply to allow for the conversion from the unit of force used for the applanator tip, gram force, into a unit of manometric pressure, millimeters of mercury.^2-4 No intrinsic corneal property was taken into account to determine this precise diameter.

This can . . . [Full Text of this Article]

AUTHOR INFORMATION
Paul M. Tesser, MD, PhD

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Applanation Area in Goldmann Applanation Tonometry—Reply
Christoph Kniestedt, Hartmut Kanngiesser, Robert L. Stamper, and Michelle Nee
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