Reproducibility and agreement between three methods of intraocular pressure measurement

The aim of the present study was to establish reproducibility between consecutive intraocular pressure measurements using the same method of tonometry as well as to assess agreement between 3 different methods of tonometry.

The study included 55 patients. Intraocular pressure of 94 eyes was measured, using Goldman applanation tonometry, Maklakoff applanation tonometry and indentation tonometry according to Schioetz method. The mean values and the differences in intraocular pressure measurements were calculated (using Bland and Altman method) in order to assess agreement between Goldman and Maklakoff applanation tonometry and Goldman and Schioetz tonometry. Reproducibility of the methods was assessed based on three consecutive intraocular pressure measurements on three groups of 20 eyes at 5-minute intervals.

The mean intraocular pressure (Po) measured by Goldman method was 23.26 +/- 0.78 mmHg, the mean pressure estimates (Po) according to Maklakoff method were 19.4 +/- 0.64 mmHg and it (Po) was 21.18 +/- 0.74 mmHg using Schioetz tonometry. The correlation (Pearson) between Goldman Po and Maklakoff Po was 0.74 and between Goldman and Schioetz Po - 0.93. Mean differences were 4.12 +/- 0.53 and 2.08 +/- 0.3 mmHg respectively. Variation coefficients between consecutive measurements were: for Goldman tonometry - 2.00%, for Maklakoff - 7.90% and for Schioetz - 5.72%.

According to Bland and Altman method there is low agreement between intraocular pressure estimates obtained by Goldman and Maklakoff tonometry, i.e. these methods are not interchangeable. This fact might be explained by the high variation coefficient of Maklakoff method. The low variation coefficient of Goldman tonometry makes it the most accurate of the three methods.