Effect of central corneal thickness on Goldmann applanation tonometry measures - a different result with different pachymeters

To assess whether the use of Orbscan pachymetry, as an alternative to ultrasound pachymetry, had an effect on the IOP-CCT relationship for Goldmann tonometry in normal human eyes. The right eye of 50 healthy subjects, aged 19 to 82 years, were assessed by Orbscan (three scans), and then central corneal thickness (CCT) measured by ultrasound pachymetry (three readings) and Goldmann tonometry performed (three readings). Goldmann tonometry indicated average IOP values from 9.7 to 20 mm Hg (group mean 14.3 +/- 2.5 mm Hg) that were highly highly correlated with ultrasound pachymetry (r=0.608, p < 0.001). Orbscan central zone pachymetry (2-mm sample zone) yielded higher values than ultrasound, averaging 0.591 +/- 0.044 mm compared to 0.523 +/- 0.037 mm (p < 0.001), with the differences between the instruments being proportional to the average thickness (p < 0.001; r=0.461). Notwithstanding, the Goldmann tonometry values were still highly correlated with the Orbscan central zone thickness data (r=0.595, p < 0.001); but, due to the difference in the thickness data generated by the two pachymeters, the absolute slope of the IOP-CCT relationship was slightly less if Orbscan measures were used, with or without use of the acoustic factor. Orbscan measures of the thickness of a central corneal zone can be used to assess the impact of central corneal thickness on Goldmann tonometry data.