Goldmann Applanation Tonometry And Central Corneal Thickness: A Comparison Of Four Correction Factor Formulas.

PURPOSE: It is now widely accepted that measured intraocular pressure (lOP) varies in
relation to central corneal thickness (CCT). This study compares four proposed formulas for adjusting the measured pressure to determine what, if any, statistical difference exists between the various methods when applied to matched sets of lOP and CCT measurements.
SUBJECTS AND METHODS: lOP and CCT values were measured in 66 eyes using
Goldmann Applanation Tonometry (GAT) and ultrasound pachymetry. From the
matched data sets obtained, correction values were calculated using four different
formulas. The results were then compared using single factor analysis of variance and
the Tukey-Kramer honestly significant difference (HSD) test to determine any statistical
difference between the results of the four formulas.
RESULTS: No statistical difference exists between the results ofthe formulas proposed
by Shimmyo, Herndon, and Stodtmeister. The results of the Ehlers formula were
statistically different from the other three.
CONCLUSIONS: The results of three different formulas for the correction of measured
lOP based on CCT are statistically the same. These formulas provide a more
conservative adjustment of the measured pressure and are based on an assumed thicker "normal" average CCT.