Corneal astigmatism in applanation tonometry

Abstract

Purpose: This short study aims at quantitatively correlating scale readings of the Goldmann tonometer to corneal curvatures in one and the same eye.

Methods: A total of 30 eyes of 21 adult patients who presented themselves in clinical practice for routine examination were arbitrarily selected. Corneal curvatures were measured in the horizontal and vertical meridians and then applanation tension measured in the same order. The data were submitted to statistical analysis by computer using Microsoft Excel and SAS System programs. Results All cases exhibited a strong positive correlation of tonometric readings to corneal curvature, that is, the flatter the curvature, the lower the reading on the scale of the tonomer, and vice versa.

Conclusion: The numbers on the scale of the Goldmann tonometer may not represent true intraocular pressure in mmHg because their values depend on a number of variables of the globe, including corneal astigmatism. Attention to these influences may help interpret the tonometric record in difficult cases.